MF研究者総覧

研究者データベース

詳細
木村　克輝(キムラ　カツキ)
工学研究院　環境工学部門　環境工学
教授
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Last Updated :2024/05/09

基本情報

所属

  • 工学研究院　環境工学部門　環境工学

職名

  • 教授

学位

  • 博士(工学)（北海道大学）

J-Global ID

研究キーワード

  • メンブレンバイオリアクター   医薬品   膜による水処理   下水道   上水道   水処理   Application of Membrane Technology   Water works   Water Treatment   

研究分野

  • 社会基盤（土木・建築・防災） / 土木環境システム
  • 環境・農学 / 環境政策、環境配慮型社会
  • 環境・農学 / 環境影響評価

担当教育組織

職歴

  • 2018年 - 現在 北海道大学大学院 教授
  • 2005年 - 2018年 北海道大学大学院助教授（准教授）
  • 1997年 - 2005年 北海道大学大学院助手
  • 2001年 - 2002年 文部科学省在外研究員（コロラド大学土木建設環境工学科）

学歴

  •         - 1997年   北海道大学   工学研究科   衛生工学専攻
  •         - 1997年   北海道大学

所属学協会

  • 日本膜学会   International Water Association   日本水環境学会   土木学会   

研究活動情報

論文

  • Akira Hafuka, Yuma Okuda, Kazuto Sano, Jumpei Ueda, Katsuki Kimura
    Water Research 120412 - 120412 2023年07月 [査読有り]
  • Helmano Fernandes, Soichiro Kiuchi, Takayuki Kakuda, Akira Hafuka, Toru Tsuchiya, Yoshihiko Matsui, Katsuki Kimura
    Journal of Water Process Engineering 53 103860 - 103860 2023年07月 [査読有り]
  • Michael Joseph Rocco, Akira Hafuka, Toru Tsuchiya, Katsuki Kimura
    Membranes 2023年03月03日 [査読有り]
  • Takayuki Kakuda, Rin Naito, Ayana Suzuki, Akira Hafuka, Katsuki Kimura
    Journal of Environmental Management 328 116863 - 116863 2023年02月 [査読有り]
  • Hideki Sakamoto, Akira Hafuka, Toru Tsuchiya, Katsuki Kimura
    Separation and Purification Technology 301 121950 - 121950 2022年11月 [査読有り]
  • Kanta Tominaga, Rina Nagai, Akira Hafuka, Wenzheng Yu, Katsuki Kimura
    Journal of Membrane Science 658 120714 - 120714 2022年09月 [査読有り]
  • Toru Sugiyama, Yui Ito, Akira Hafuka, Katsuki Kimura
    Water Research 118810 - 118810 2022年08月 [査読有り]
  • Akira Hafuka, Sota Fujino, Katsuki Kimura, Kazuyuki Oshita, Naoya Konakahara, Shigetoshi Takahashi
    Science of The Total Environment 828 154573 - 154573 2022年03月 [査読有り]
  • Akira Hafuka, Katsuki Kimura
    Membranes 12 1 99  2022年01月 [査読有り]
  • 山本 祐士朗, 小野 順也, 永井 梨奈, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 78 7 III_177 - III_184 公益社団法人 土木学会 2022年 [査読有り]
     
    膜を用いた上下水処理には従来の方法と比較して様々な利点がある一方で，膜ファウリングが大きな問題となる．近年の研究において，バイオポリマーと総称される高分子量親水性有機物が膜ファウリングの発生に強く関与することが示唆されている．しかし水中バイオポリマーの組成，構造，特性については不明な点が未だに多い．本研究では水道原水，下水処理水よりバイオポリマーを回収・精製し，特定の多糖，タンパク質に対応する酵素(α-アミラーゼ，セルラーゼ，プロテアーゼ，リゾチーム)によるこれらの分解性を検討した．LC-OCDを用いることで，一般的な水質分析では検知できない酵素による分解性(バイオポリマーの低分子化)を把握することができた．水道原水より回収したバイオポリマーではα-アミラーゼとセルラーゼによる分解が卓越したのに対し，下水処理水より回収したバイオポリマーではリゾチームによる分解が卓越した．この結果は本研究で分析した2種類のバイオポリマーの構造と特性が大きく異なることを明示するものであり，これまでに得られていない知見である．本研究で確立したバイオポリマーの酵素分解性評価手法を用いて様々なバイオポリマーと酵素の組み合わせを検討することにより，これまで詳細が不明となっていたバイオポリマーの構造解明を進展させられる可能性がある．
  • 中川 颯人, 木内 壮一朗, Helmano Fernandes, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 78 7 III_143 - III_148 公益社団法人 土木学会 2022年 [査読有り]
     
    膜分離活性汚泥法には活性汚泥法と比べて多くの長所があるが，膜ファウリングが問題となる．本研究グループではこれまでに気泡径数百nmの気泡を含む水（ナノバブル水）を用いた膜の逆洗はMBRの膜ファウリング抑制に有効となりうることを見出しているが，逆洗条件の詳細な検討は行われていない．本研究ではMBRファウリング物質のモデル化合物として多用されるアルギン酸ナトリウムによりファウリングを発生させたセラミック平膜を用い，ナノバブル逆洗の洗浄効果が高くなるような洗浄方法を検討した. 本研究では筆者らが従来用いてきたナノバブル水による洗浄効果は小さかったが、より高濃度のナノバブル水を用いることで洗浄効率が上昇することが確認された. ナノバブル逆洗の洗浄効果が高くなる理由はナノバブル崩壊時に発生するラジカルの関与ではなく，ナノバブルがファウリング層の構造を弛緩させたことに伴う物理的洗浄の高効率化が主であると考えられた．
  • 佐野 航士, 奥田 雄眞, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 78 7 III_359 - III_368 公益社団法人 土木学会 2022年 [査読有り]
     
    リン酸態リン（PO4-P）は生物利用性が高いため，湖沼での有害藻類ブルーム発生を防ぎ，水環境を保全するためにもPO4-P濃度のモニタリングは必要不可欠である．しかし，一般的なグラブサンプリングとPO4-P分析では，得られる濃度の代表性と分析方法の感度に課題がある．そこで本研究では，河川および湖沼において低濃度で存在するPO4-Pの時間平均濃度をパッシブサンプリングによって推定した．その結果，サクシュコトニ川ではグラブサンプリングで得た試料水中の溶存態リン濃度と近い時間平均PO4-P濃度が算出された．茨戸湖でのパッシブサンプリングでは通常は定量が困難な低濃度のPO4-Pに対し，その時間平均濃度の鉛直分布を得ることができた．
  • 鹿沼 俊介, 藤野 創太, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 78 7 III_33 - III_41 公益社団法人 土木学会 2022年 [査読有り]
     
    嫌気性MBRにおけるSRTの延長とHRTの短縮が下水汚泥消化効率に与える影響を明らかにするため，SRTを3条件（30，60，90日），HRTを2条件（30，15日）設定し，各運転条件における糖，タンパク質および脂質の分解率を求めた．それら有機物分解率はSRTが30日の条件に比べ，60日や90日と長い条件において上昇した．バイオガス生成速度はHRT短縮に伴う有機物負荷上昇により，HRTが30日の条件に比べ15日での運転において約2倍に増加した．膜間差圧は最大で41kPaに達したが，比較的内径の大きい中空糸膜を用いてクロスフローろ過を行ったことで154日間膜洗浄および交換を行わずに連続膜ろ過がなされた．運転終了後の膜洗浄の結果，不可逆的無機ファウリングが支配的であった．無機ファウラントとしてCa，PおよびMgが多く抽出された．
  • 中村 拓海, 角田 貴之, 羽深 昭, 小野 将嗣, 木村 克輝
    土木学会論文集Ｇ（環境） 78 7 III_135 - III_142 公益社団法人 土木学会 2022年 [査読有り]
     
    本研究では膜の細孔径または材質のみが異なる膜を用意し，実都市下水を原水とするベンチスケールMBRを用いて定流量ろ過を行い，ファウリングの進行速度を比較した．同じ材質（CPVC製），同様の開孔率で細孔径が異なるUF膜とMF膜を用いた実験では，両膜のファウリングの進行速度にほとんど差はなかった．局所的フラックスが同程度であれば細孔径がファウリング発生に及ぼす影響は小さいことが本実験では示唆された．膜構造がほぼ同様のCPVC製UF膜とPVDF製UF膜を用いた実験では，CPVC製膜の方がPVDF製膜よりもファウリングの進行速度が速かった．本研究で設定したフラックス範囲（0.72-0.90m/d）において，PVDFはCPVCに比べファウリング発生を抑制できる膜材質である可能性が示された．本研究で発生したファウリングはいずれもバイオポリマーを主な構成成分とする膜表面ゲル層によるものであったが，SEM観察およびFT-IR分析ではゲル層特性の差異を検討することはできなかった．
  • Akira Hafuka, Yoichi Tsubokawa, Ryuichiro Shinohara, Katsuki Kimura
    Environmental Pollution 288 117732  2021年11月 [査読有り]
     
    Phosphorus (P) discharges from human activities result in eutrophication of lakes. We investigated whether the forms of phosphorus (P) in rivers with high effluent loads flowing through urban areas of Sapporo, Japan, were transformed when transported downstream into a eutrophic lake, namely Lake Barato. We hypothesized that the inorganic P supplied from the rivers might be transformed to organic forms in the lake. The results showed that soluble reactive phosphorus (SRP) and particulate inorganic phosphorus (PIP) dominated in the river discharge to the lake. Suspended solids in the rivers were rich in iron (Fe) so PIP was associated with Fe. A comparison of the concentrations at the river mouth and 4.5 km downstream showed that the concentrations of SRP and PIP were lower at 4.5 km downstream than at the river mouth, whereas the concentrations of organic P (i.e., dissolved organic phosphorus and particulate organic phosphorus) were similar. The results from solution 31P nuclear magnetic resonance spectroscopy of lake water showed that pyrophosphate was only present in the particulate fraction, while orthophosphate diesters (DNA-P) were only present in the dissolved fraction. Riverine samples contained orthophosphate (ortho-P) only, while lake samples contained ortho-P, orthophosphate monoesters, and DNA-P. The results suggest that the P forms, particularly those of dissolved P, shifted from inorganic to organic forms as the water was discharged from the river to the lake.
  • Katsuki Kimura, Mutsumi Yamakawa, Akira Hafuka
    Chemosphere 277 2021年08月 [査読有り]
     
    The recovery and utilization of organic matter in municipal wastewater are essential for the establishment of a sustainable society, such that these factors have drawn significant recent attention. The up-concentration of organic matter via direct membrane filtration (DMF), followed by anaerobic digestion, is advantageous over the treatment of the entire wastewater by an anaerobic process, such as an anaerobic membrane bioreactor (AnMBR). However, the occurrence of severe membrane fouling in the DMF is a problem. In this study, DMF was carried out at an existing wastewater treatment plant to attempt long-term operation. A combination of vibration of membrane modules, short-term aeration, and chemically enhanced backwash (CEB), with multiple chemicals (i.e., the alternative use of citric acid and NaClO), was found to be effective for the mitigation of membrane fouling in DMF. Furthermore, switching the feed from influents to effluents in the primary sedimentation basin significantly mitigated membrane fouling. In this study, in which microfiltration membrane, with a nominal pore size of 0.1 μm, was used, ∼75% of the organic matter in raw wastewater was recovered, with the volumetric concentration of wastewater by 50- or 150-fold. Organic matter recovered by DMF had significantly higher potentials for biogas production than the excess sludge generated from the same wastewater treatment plant. An analysis of the energy balance (i.e., the energy used for DMF and recovered by DMF) suggests that the proposed DMF can produce a net-positive amount of electricity of ∼0.3 kWh from 1 m3 of raw wastewater with a typical strength (chemical oxygen demand of 500 mg/L).
  • Takayuki Kakuda, Hiroyuki Iwasaki, Xia Huang, Katsuki Kimura
    Journal of Water Process Engineering 40 2021年04月 [査読有り]
     
    In this study, a pilot-scale membrane bioreactor (MBR) treating municipal wastewater was operated over 600 d. Intensive monitoring of sludge filterability with high frequency, which is rarely reported in previous studies, was performed. Detailed information on sludge filterability obtained in this study makes the advanced interpretation of membrane fouling possible and allows to take effective countermeasures. Two methods (batch membrane filtration and measurement of capillary suction time (CST)) were used to assess sludge filterability, which significantly varies during the long-term operation. Although these two methods generated similar data, the CST measurement is easier than batch-filtration and is therefore recommended for intensive monitoring of sludge filterability in MBRs. Using the data obtained in this study, the evolution of reversible and irreversible fouling was distinguished. The importance of separately assessing the impact of colloidal matter on sludge filterability was also demonstrated: colloidal matter caused the deterioration of sludge filterability. To detect such impacts, the frequency of the assessment should be sufficiently high. A new method (modification of CST measurement) proposed in this study could be used for such frequent assessments. Temperature in the reactor and ion balance in raw wastewater were identified as key factors in the deterioration of sludge filterability. A specific fraction of polysaccharides (lipopolysaccharides) exhibited a significant correlation with the deterioration of sludge filterability. This study can provide important information for the operation and maintenance of large-scale MBRs treating municipal wastewater.
  • 伊藤 結衣, 杉山 徹, 高橋 威胤, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 77 7 III_339 - III_345 公益社団法人 土木学会 2021年 [査読有り]
     
    都市下水中の有機物と栄養塩（リン，窒素）は重要な資源である．都市下水から有機物を回収する方法の一つに下水直接膜ろ過（Direct Membrane Filtration, DMF）があり，流入下水中有機物の75-80%を安定して濃縮回収することができる．これまでに報告されているDMF検討例のほとんどで栄養塩の回収は行われず，処理水（膜透過水）に栄養塩が残存していた．本研究ではDMF前段においてリン吸着性能を付与した微生物担体を用いたリン吸着を，DMF後段においてイオン交換による膜透過水中アンモニアイオンの吸着を試みた．実下水を用いた実験で，リンに関しては75%，アンモニアイオンに関しては80%を回収できることが示された．アンモニアイオンの回収については，ナノろ過を導入して共存多価イオンの影響を排除することで，さらに回収率を高められることを確認できた．
  • 小野 順也, 永井 梨奈, 冨永 勘太, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 77 7 III_321 - III_328 公益社団法人 土木学会 2021年 [査読有り]
     
    膜を用いた浄水処理には従来の処理と比較して様々な利点がある一方で，膜ファウリングが大きな問題となる．近年の研究においてバイオポリマーと総称される高分子量親水性有機物が膜ファウリングの発生に強く関与することが示唆されている．本研究では特徴の異なる複数の原水よりバイオポリマーを回収・精製し，これらが発生させる膜ファウリングの差異について検討した．バイオポリマー濃度を統一して実施した膜ろ過試験では原水毎に膜ファウリング発生速度が明らかに異なっており，原水が異なるとバイオポリマーの特性が変化することが示された．バイオポリマー特性の差異はLC-OCDを用いた分子量分布測定，赤外スペクトル分析においても明白であり，バイオポリマーの大半が多糖類より構成される場合には不可逆的ファウリングの発生をより深刻にする可能性が示された．消散監視機能付き水晶振動子マイクロバランス（QCM-D）による分析では興味深い結果が得られた．QCM-D分析において膜材質ポリマーであるPVDFとの高い親和性が示されたバイオポリマーが高い膜ファウリングポテンシャルを有していた．また，バイオポリマーの粘弾性がファウリングの可逆性を説明する可能性が示唆された．今後QCM-Dを用いた分析データを充実させていくことで，膜ファウリングが発生しにくい膜材質を適切に選定できる可能性がある．
  • Yusuke Ninomiya, Katsuki Kimura, Tsubasa Sato, Takayuki Kakuda, Masashi Kaneda, Akira Hafuka, Toru Tsuchiya
    Water Research 181 115881 115881 - 115881 2020年08月 [査読有り][通常論文]
  • Akira Hafuka, Taketsugu Takahashi, Katsuki Kimura
    Biochemical Engineering Journal 107692 - 107692 2020年06月 [査読有り][通常論文]
  • Katsuki Kimura, Keita Kume
    Journal of Membrane Science 602 117975 - 117975 2020年05月 [査読有り][通常論文]
  • T. Kakuda, H. Iwasaki, K. Kimura
    Water Science and Technology 81 3 529 - 534 2020年02月01日 [査読有り][通常論文]
     
    Abstract Sludge filterability in membrane bioreactors (MBRs) fluctuates and affects membrane fouling. Therefore, understanding the reasons for the fluctuations of sludge filterability is important for the efficient operation of MBRs. In this study, a pilot-scale MBR treating municipal wastewater was operated for about 600 days and the variations in sludge filterability were continuously monitored by batch-filtration experiments using the same membranes as in the MBR. To investigate the reasons for the deterioration of sludge filterability, constituents in sludge supernatant were intensively monitored, and the correlations with sludge filterability were determined. The concentration of lipopolysaccharides (LPS) in sludge supernatant exhibited significantly higher correlation with sludge filterability than did conventional indexes (i.e. polysaccharides and proteins). Size fractions affecting MBR sludge filterability were also investigated, and it was suggested that colloidal LPS deteriorated MBR sludge filterability. Based on the long-term operation of the MBR, increase in colloidal LPS under low temperatures of the mixed liquor suspension was a key factor in the deterioration of sludge filterability. The impact of LPS increasing under low temperatures should be investigated by operating bench-scale MBRs fed with synthetic wastewater in controlled conditions.
  • 杉山 徹, 山川 むつみ, 高橋 威胤, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 76 7 III_227 - III_234 公益社団法人 土木学会 2020年 [査読有り]
     
    都市下水中に含まれる有機物は新たなエネルギー源として見なすことができる．しかし，下水中からのエネルギー回収に必要なプロセスである嫌気性消化を直接適用するためには，有機物を濃縮する必要がある．下水を直接膜ろ過し，有機物を濃縮することで嫌気性消化の適用は容易となり下水からのエネルギー回収量を大幅に増加させることができる．しかし，膜ファウリングの発生と透過水中の有機物濃度の高さが課題となる．本研究では，下水直接膜ろ過の前処理としてスポンジ担体を用いた生物膜処理を導入し，ファウリング抑制効果と膜透過水中有機物濃度の低減を試みた．生物膜処理において，HRTとDOを変化させることにより有機物除去を調節し，回収可能となる有機物量（流入下水中有機物の約75%）を維持したまま膜透過水中有機物濃度を低減させることができた．低水温期（10.9-12.6℃）に実施した実験では，前処理による膜ファウリング発生は抑制された．水温が上昇した（13.9-16.8℃）期間に実施した実験では微生物活動が活性化し，前処理を導入した系列ではバイオポリマーに起因すると考えられる膜ファウリングの発生が顕著になった．一方で水温上昇時に前処理を導入した系列では，膜透過水中のBOD濃度は約7 mg/Lとなり，従来の下水処理法と同程度のBOD濃度となった．
  • 内藤 りん, 角田 貴之, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 76 7 III_165 - III_171 公益社団法人 土木学会 2020年 [査読有り]
     
    本研究では実都市下水を処理するパイロットスケールMBRを300日以上連続運転し，MBR汚泥中で汚泥ろ過性に影響を及ぼす成分の季節変動を追跡した．MBR汚泥中のコロイド画分TOC，溶解性リポ多糖（LPS）濃度およびバイオポリマー濃度とMBR汚泥ろ過性との間に強い相関が認められた．MBR汚泥中で膜ファウリングに影響を及ぼすサイズ画分を検討した結果，0.45µm以上1.0µm以下および5.0µm以上11µm以下のコロイド成分が膜ファウリングの発生に強い影響を及ぼすことが示唆された．また，MBR汚泥中バイオポリマーを分離・精製し，従来の研究においてバイオポリマーのモデル物質として用いられてきたアルギン酸ナトリウムとの比較を行った．MBR汚泥中のバイオポリマーはアルギン酸ナトリウムよりも深刻な膜ファウリングを発生させ，従来の想定よりも高い膜ファウリングポテンシャルを有することが示唆された．
  • 木内 壮一朗, Helmano Fernandes, 羽深 昭, 木村 克輝
    土木学会論文集Ｇ（環境） 76 7 III_149 - III_155 公益社団法人 土木学会 2020年 [査読有り]
     
    膜分離活性汚泥法(MBR)は活性汚泥法と比べて様々な長所があるが，運転中に発生する膜ファウリングが問題となっている．様々なタイプの汚れに対して洗浄効果が報告されているマイクロバブル・ナノバブルはファウリングが発生した膜を効率的に洗浄できる可能性がある．本研究では，ベンチスケールMBRを用いて，マイクロバブル・ナノバブルの膜洗浄効果に関する基礎的検討を行った．マイクロバブルを用いた浸漬洗浄では大きな洗浄効果が確認された．ナノバブルは浸漬洗浄では十分な洗浄効果を発揮しなかったが，粒状担体流動と併用しながら逆洗水に混入させることで化学薬品を用いた逆洗と同等以上の洗浄効果が確認された．ナノバブルによってMBR汚泥に及ぼす悪影響は，化学薬品の使用によって及ぼされるものより小さいことが示された．
  • Z. Liu, Xianzheng Zhu, Peng Liang, Xiaoyuan Zhang, Katsuki Kimura, Xia Huang
    Journal of Membrane Science 588 2019年10月 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. Polymeric flat-sheet membrane (FS) and ceramic flat-tubular membrane (CM) are the most widely-used membranes in anaerobic membrane bioreactor (AnMBR). However, fouling mechanism on FS and CM were rarely compared before and needed to be deeply illuminated. In this work, distinction of irremovable fouling formed on polyvinylidene fluoride FS and Al2O3 CM in AnMBR treating municipal wastewater was studied. Lab-scale AnMBR operation showed that FS presented severer irremovable fouling and faster fouling rate. Foulants characterization revealed that irremovable fouling of FS was composed of more organics (FS = 0.91, CM = 0.35 g-TOC/m2-membrane) and biomass (FS = 47.3, CM = 8.65 × 1010 cell/m2-membrane), leading to gel layer loosely structured. Conversely, irremovable fouling of CM contained more inorganics (FS = 0.08, CM = 0.55 g/m2-membrane), facilitating dense gel layer with larger specific filtration resistance. Membrane cleaning tests found that gel layer on FS was efficiently removed by NaClO, while gel layer on CM was loosened by NaClO but destructed by citric acid. NaClO/NaOH both reduced resident bacteria, whereas increased the proportion of live cells. Irreversible fouling on FS involved more organics while more inorganics on CM. Irreversible biofouling could utilize citric acid as substrate for metabolism and proliferation. This study not only helps to probe fouling mechanism with different membrane materials, but also aids to develop differentiated effective cleaning strategy to corresponding membrane modules.
  • T. Miyoshi, T. P. Nguyen, T. Tsumuraya, K. Kimura, Y. Watanabe
    Water Science and Technology 80 6 1011 - 1021 2019年09月15日 [査読有り][通常論文]
     
    Abstract We investigated the operating conditions of a baffled membrane bioreactor (B-MBR) under which long-term stable operation can be achieved through the continuous operation of a pilot-scale B-MBR. Under appropriate operating conditions, the B-MBR was capable of achieving excellent treated water quality in terms of biochemical oxygen demand and concentration of total nitrogen. Excellent removal of total phosphorus was also achieved. In addition, the degree of membrane fouling was acceptable, indicating that stable continuous operation of a B-MBR is possible under the operating conditions adopted in the present study. Estimation of the specific energy consumption in hypothetical full-scale B-MBRs operated under the conditions recommended by the findings was also performed in this study. The results suggest that energy consumption in full-scale B-MBRs would be in the range of 0.20–0.22 kWh/m3. These results strongly suggest that energy consumption in MBR operation can be significantly reduced by applying the concept of a B-MBR.
  • Katsuki Kimura, Takayuki Kakuda, Hiroyuki Iwasaki
    Separation and Purification Technology 223 224 - 233 2019年09月 [査読有り][通常論文]
     
    © 2019 Polysaccharides were identified as key foulants in membrane bioreactors (MBRs) in previous studies. Polysaccharides used for MBR fouling research should represent real foulants, and alginate and dextran have often been used as model polysaccharides. However, their properties are not necessarily similar to those of polysaccharides that actually cause membrane fouling in MBRs. In recent studies, it was shown that polysaccharides causing membrane fouling in MBRs had the structures of lipopolysaccharides (LPSs), which are components of the cell wall of gram-negative bacteria. In the present study, therefore, membrane fouling caused by commercially available LPSs was investigated and was compared with that caused by model polysaccharides. In a series of batch filtration tests using four different microfiltration (MF) and ultrafiltration (UF) membranes, regardless of the membrane used, LPSs caused more severe membrane fouling than did alginate or dextran when they were filtered under the condition of the same organic carbon concentration. The properties of LPSs were found to be considerably different from those of alginate and dextran. In particular, affinity of LPS to PVDF polymer assessed by quartz crystal microbalance (QCM) mass measurement was remarkably high, and it would account for the severe fouling caused by LPSs. In experiments with filtering of mixtures of the model polysaccharides and a biomass suspension collected from a pilot-scale MBR, which were conducted to mimic the sudden increase in dissolved polysaccharides in real MBRs, LPS induced significant irreversible fouling, while alginate and dextran did not. The results obtained in this study clearly demonstrated high fouling potential of LPSs. Use of LPSs in future MBR fouling studies is therefore recommended.
  • Yue Gao, Zhou Fang, Peng Liang, Xiaoyuan Zhang, Yong Qiu, Katsuki Kimura, Xia Huang
    Bioresource Technology 204 - 210 2019年03月 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Sewage can become a valuable source if its treatment is re-oriented. Forward osmosis (FO) is an effective pre-treatment for concentrating solutions. A laboratory-scale anaerobic digestion (AD) bioreactor was setup for the treatment of concentrated real sewage by FO membrane to investigate the removal of chemical oxygen demand (COD) and biogas production. Inhibitory batch tests were carried out for the impact of NaCl and NH 4+ -N. Results showed that the concentrated sewage could be purified with 80% COD removal, and energy recovery could be achieved. But the process was inhibited. The results of inhibitory batch test showed that (i) when the NH 4+ -N concentration was lower (<200 mg/L), the biogas production was promoted, when it went high, the inhibition appeared; (ii) single existence of NaCl had negative influence on methane production; (iii) the inhibition was more severe with co-existence of NaCl and NH 4+ -N. The AD performance could be recovered via sludge acclimation.
  • Katsuki Kimura, Hiroki Uchida
    Water Research 21 - 28 2019年03月 [査読有り][通常論文]
     
    © 2018 Intensive membrane cleaning can be used with ceramic membranes since they are physically/chemically robust. It might therefore be possible for membrane bioreactors (MBRs) to be operated under the condition of a high membrane flux when ceramic membranes are used with such intensive membrane cleaning. In this study, bench-scale MBRs equipped with flat-sheet ceramic membranes were operated for long periods. Circulation of granular materials (cylindrical polyurethane) in the tank and frequent chemically enhanced backwash (CEB) were used as intensive physical cleaning and chemical cleaning in this study, respectively. Experiments were carried out with synthetic wastewater. The use of granular materials, which can cause significant damage to polymeric membranes (Kurita et al., 2015), was effective for controlling the formation of cake (deposition of microbial flocs) on the surface of the ceramic membranes. When both mechanical cleaning using the granular materials and CEB with 1000 ppm of sodium hypochlorite (NaClO) were applied, contrary to an expectation, evolution of reversible fouling (formation of a transparent gel layer on the membrane surface) became uncontrollable, whereas irreversible fouling was effectively controlled. The use of NaClO induced release of organic macromolecules via biomass decay, leading to the evolution of reversible fouling. When the intensity of CEB with NaClO was adequately lowered, with the aid of the mechanical cleaning using the granules, the bench-scale MBR could be operated stably under an elevated membrane flux for a long period (>70 days). It was postulated that the adjustment of CEB intensity preferably altered properties of organic macromolecules released from biomass: the structure of the gel layer was porous when the CEB intensity was lowered. When CEB is used in MBRs, it is thus important to balance cleaning efficiency and its harmful effect on biomass. When adequate CEB is used with intensive mechanical cleaning, MBRs with ceramic membranes can be operated under high flux conditions.
  • 野村 洋平, 三好 太郎, 西内 友也, 木村 克輝, 藤原 拓
    土木学会論文集Ｇ（環境） 75 7 III_359 - III_365 公益社団法人 土木学会 2019年 [査読有り]
     
    ポリアミド活性層の正浸透膜を用いた正浸透法による下水の直接処理を検討するとともに，膜ファウリングに寄与する溶存有機物特性の評価を試みた．ろ過下水を供給液(FS)に，3Mの塩化ナトリウム溶液を駆動液に使用し，処理中の膜透過水fluxおよび溶存有機物の挙動を調査した．14時間の処理により膜透過水fluxは18.7L/m2/hから9.9L/m2/hまで低下したものの，溶存有機炭素の阻止率は98%と極めて高かった．FSに含まれる溶存有機物の一部はファウリング層内に蓄積していたことから，液体クロマトグラフィー–有機炭素検出器を用いて，ファウリング層内の各溶存有機物画分を分析した．その結果，FS中に存在したバイオポリマー画分の15%以上は膜表面に蓄積していたのに対して，他の有機物画分の膜表面蓄積率は1–2%であったことから，主たる溶存性有機系ファウラントがバイオポリマー画分であると推定された．
  • T. Miyoshi, T. Tsumuraya, T. P. Nguyen, K. Kimura, Y. Watanabe
    Water Science and Technology 77 2803 - 2811 2018年08月 [査読有り][通常論文]
     
    © IWA Publishing 2018. In this study, we investigated the effects of recirculation and separation times on removals of organic matter, nitrogen, and phosphorus in a baffled membrane bioreactor (B-MBR) treating real municipal wastewater. A pilot-scale B-MBR experimental apparatus was operated under two different sets of recirculation and separation times. The results revealed that, irrespective of operating conditions, the biochemical oxygen demand (BOD) and concentration of total nitrogen (T-N) in the treated water can be lowered to less than 3 and 5 mg/L, respectively. Although T-N was effectively removed in the two different operating conditions, increase in the fraction of recirculation time results in tiny deterioration of nitrogen removal efficiency in the B-MBR. Phosphorus removal efficiency was also slightly decreased as the fraction of recirculation time (ratio between recirculation and separation times) was increased. The results of the measurement of dissolved oxygen (DO) profiles at different points of the B-MBR apparatus indicate that the increase in DO concentration in the anoxic zone of the B-MBR becomes much more pronounced by increasing recirculation intensity. On the basis of the results obtained in this study, it can be concluded that efficient removal of BOD, T-N, and total phosphorus can be achieved by the B-MBR as long as appropriate recirculation intensity is selected.
  • Katsuki Kimura, Koki Shikato, Yasumitsu Oki, Keita Kume, Stefan A. Huber
    Journal of Membrane Science 554 83 - 89 2018年05月15日 [査読有り][通常論文]
     
    With the widespread application of liquid chromatography with organic carbon detection (LC-OCD) to investigate membrane fouling in low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF), membrane fouling by macromolecular hydrophilic biopolymer fraction has been recognized. In this study, a drinking water source was intensively investigated over 16 months. Membrane filtration using hollow-fiber MF membranes was carried out in constant flux mode with periodic backwashing, and two pretreatments (aluminum coagulation and anion exchange) were examined in terms of biopolymer removal and fouling mitigation. Higher biopolymer removal rates achieved by anion exchange than coagulation did not cause better control of membrane fouling in MF. Coagulation and anion exchange removed different types of biopolymers, which implied diversity in the biopolymer fraction. A modified set-up of LC-OCD analysis in which two different columns were sequentially connected was examined. It was demonstrated that the biopolymer fraction detected as a single peak with molecular weight of > 10,000 Da with the conventional LC-OCD set-up comprised of molecules with a variety of molecular weights including > 1,000,000 Da. It was found that coagulation removed large-size biopolymers with higher fouling potentials while anion exchange preferentially removed small-size biopolymers with lower fouling potential. Concentration of large-size biopolymers in the feed water collected on different dates correlated with the degree of membrane fouling. In an attempt to generalize the conclusion drawn from the experiments using the specific drinking water source, batch MF tests filtering biopolymers isolated from different drinking water sources were also carried out. Importance of the large-size biopolymer fraction in the evolution of membrane fouling was also suggested with different drinking water sources.
  • Katsuki Kimura, Daisuke Honoki, Taku Sato
    SEPARATION AND PURIFICATION TECHNOLOGY 181 37 - 43 2017年06月 [査読有り][通常論文]
     
    Organic matter in municipal wastewater should be regarded as a resource for energy production in the future. Direct application of anaerobic digestion to municipal wastewater is easy if the concentration of organic matter is increased. Although microfiltration membranes can concentrate organic matter in raw municipal wastewater, severe membrane fouling is likely to occur. In this study, efficient physical cleaning methods for direct membrane filtration (DMF) of municipal wastewater were investigated. Agitation of the tank, vibration of membrane modules, and use of granular materials were examined. Aeration was not tested because it leads to microbial degradation of organic matter (loss of recoverable energy). No single cleaning method worked well for DMF. However, a combination of membrane vibration and agitation of the tank was found to be effective. When the effective physical cleaning was performed with chemically enhanced backwash using citric acid and an adequate membrane flux, DMF of real municipal wastewater could be continued for almost one month without conducting any off-line membrane cleaning. The increase in transmembrane pressure was almost perfectly controlled in the long-term operation, during which 75% of organic matter was successfully recovered and 50-fold concentration (based on volume) of wastewater was continuously achieved with hydraulic retention time of 3.1 h. (C) 2017 Published by Elsevier B.V.
  • Katsuki Kimura, Yasumitsu Oki
    WATER RESEARCH 115 172 - 179 2017年05月 [査読有り][通常論文]
     
    In recent studies on membrane fouling in microfiltration (MF) and ultrafiltration (UF) for drinking water production, hydrophilic macromolecular organics referred to as biopolymers have been shown to be major players in the fouling. In this study, various pretreatments were compared to maximize removal of biopolymers and to control membrane fouling efficiently. Multiple water samples were collected from different drinking water sources and were used in this study. Coagulation using polyaluminum chloride (PACl) was carried out under conditions of different dosages and different pHs and was also carried out in combination with the use of powdered activated carbon (PAC) or magnetic ion exchange (MIEX (R)) resin. The efficiency of removal of biopolymers was highest by the combination of MIEX (R) and coagulation regardless of the type of sample. Efficient removal of biopolymers achieved by the combination of MIEX (R) and coagulation led to efficient control of membrane fouling in MF, which was confirmed by bench-scale filtration tests conducted under a constant flux of 62.5 LMH using commercially available hollow-fiber membranes. Enhanced coagulation with increased coagulant dosage or acidic coagulation (pH = 6) also exhibited good removal of biopolymers in some cases and led to control of fouling. In contrast, the combination of PAC and coagulation sometimes caused more rapid evolution of fouling by forming cake layers on the membrane surface. Results of bench-scale tests showed that the concentration of biopolymers in the feed water correlated well with the degree of physically irreversible fouling, which was dominant in this study. The strong correlation was shown with multiple water samples treated by various pretreatments, demonstrating that biopolymer concentration in feed water is a good index for fouling studies. (C) 2017 Elsevier Ltd. All rights reserved.
  • Tokihiro Kurita, Takuma Mogi, Katsuki Kimura
    SEPARATION AND PURIFICATION TECHNOLOGY 169 43 - 49 2016年09月 [査読有り][通常論文]
     
    It has been reported that the combination process of biofilm and submerged membrane bioreactors (MBRs) can mitigate membrane fouling. In this study, the influence of using three different biofilm carriers (fixed rope carrier, moving granular carrier and moving sponge carrier) on the operation and membrane fouling of MBRs was investigated. Using rope or sponge carriers with MBR processes improved the removal efficiency of nitrogen via the creation of an anoxic part inside the carriers. However, membrane fouling became very severe when rope carriers were used. Using granular or sponge carriers effectively mitigated membrane fouling because they mechanically cleaned the membrane surface. The cake/gel layer on the membrane surface was perfectly removed by granular or sponge carriers. However, the deterioration of the filterability of the mixed liquor suspensions was significant with granular carriers, leading to the evolution of physically irreversible fouling, whereas such deterioration was insignificant with the sponge carrier. The characteristics of the soluble microbial products (SMP) significantly varied depending on the types of carriers used, which could influence the filterability of mixed liquor suspensions and the development of irreversible membrane fouling. (C) 2016 Elsevier B.V. All rights reserved.
  • Katsuki Kimura, Nalco Ando
    SEPARATION AND PURIFICATION TECHNOLOGY 163 8 - 14 2016年05月 [査読有り][通常論文]
     
    In recent studies dealing with membrane fouling in microfiltration (MF)/ultrafiltration (UF) processes for drinking water production, biopolymers, which are hydrophilic macromolecules, have been identified as the key foulants. However, removal of biopolymers from water has been rarely focused on in previous studies. In this study, removal of biopolymers by coagulation, which is the most common pretreatment for MF/UF in existing full-scale facilities, was investigated. Surface water samples from three rivers used as raw water for drinking water production were examined in this study. Sampling was repeated in different seasons to examine a wide range of water quality. It was demonstrated that dosages commonly used in existing facilities were insufficient to maximize biopolymer removal by coagulation conducted at neutral pH. It was shown that an extremely high dosage of the coagulant was necessary to maximize biopolymer removal. A new dosage index, aluminum (Al, mg/L)/biopolymer (Bp, mu g/L), was used in this study. Al/Bp of about 20 was found to be necessary at pH 7 to almost maximize biopolymer removal by coagulation regardless of the water tested. Maximized biopolymer removal brought about least evolution of membrane fouling, which was separately verified in bench-scale filtration tests. Efficiency of coagulation for biopolymer removal varied depending on the season: samples collected in the cold season exhibited poor removal of biopolymers. Detailed examinations of biopolymers in each sample suggested that properties of the biopolymers changed seasonally. (C) 2016 Elsevier B.V. All rights reserved.
  • Katsuki Kimura, Saaya Okazaki, Takeya Ohashi, Yoshimasa Watanabe
    JOURNAL OF MEMBRANE SCIENCE 501 60 - 67 2016年03月 [査読有り][通常論文]
     
    Reverse osmosis (RO) is an important technique for potable water reuse. However, the problem of membrane fouling in RO must be addressed for its widespread use. In this study, fouling in RO was investigated with 2540 membrane elements fed with effluents from a membrane bioreactor (MBR) treating municipal wastewater. The results of chemical cleaning, elemental analysis for a cross section of the fouled membrane and microwave digestion of the fouled membrane suggested that silica was a major player in the membrane fouling. Also, organic matter present in the MBR effluent (mainly composed of soluble microbial products) was found to play an important role in the evolution of membrane fouling. A unique experimental setup enabled investigation of the interaction between silica and organic matter in the membrane fouling in RO: concentrations of silica and organic matter in the feedwater were manipulated. Remarkable membrane fouling occurred only when feedwater containing both silica and organic matter was filtered. It was found that silica or organic matter alone did not cause severe membrane fouling in the RO. The co -presence of silica and organic matter seems to have synergetic effects that cause severe membrane fouling in RO. (C) 2015 Elsevier B.V. All rights reserved.
  • 木村 克輝, 大木 康充
    土木学会論文集Ｇ（環境） 72 7 III_535 - III_541 公益社団法人 土木学会 2016年 [査読無し]
     
    浄水処理への膜処理適用が進んでいるが、自然水中の有機物（Natural Organic Matter, NOM）が引き起こす膜ファウリングが広範な普及の障害となっている。本研究では、NOMの中でも近年膜ファウリングへの関与が重要視されているバイオポリマー（親水性高分子量成分）に着目し、バイオポリマーのサイズとMF/UF膜細孔径の関係が膜ファウリング発生に及ぼす影響について考察した。ポリ塩化アルミニウムによる凝集処理と、帯磁性陰イオン交換樹脂処理を用いた前処理について検討し、これらの処理では除去されるバイオポリマーの画分が異なっていることを明らかにした。凝集処理では分子量100万以上の超高分子量バイオポリマーの除去が行われる一方でイオン交換樹脂処理では分子量数万付近の低分子量バイオポリマーの除去が行われた。MF膜ファウリングの抑制効果は凝集処理を用いた場合に高まることから、超高分子量バイオポリマーのMF膜ファウリングへの重大な関与が示された。前処理におけるバイオポリマーの除去率はイオン交換樹脂処理と凝集処理を組み合わせた場合に著しく高まり、連動して膜ファウリングの抑制効果も高くなった。これは、イオン交換樹脂処理によりフミン質が極めて良好に除去され、バイオポリマーと反応しうる凝集剤量が相対的に大きくなったことによるものと考えられた。バイオポリマーが細孔内に侵入できないUF膜を用いた場合には、不可逆的ファウリングの発生が著しく抑制されたが、UF膜により抑止された微細粒子が可逆的ファウリングの発生を促進させるようになった。
  • Hiroshi Yamamura, Katsuki Kimura, Kumiko Higuchi, Yoshimasa Watanabe, Qing Ding, Akira Hafuka
    WATER RESEARCH 87 218 - 224 2015年12月 [査読有り][通常論文]
     
    While low-pressure membrane filtration processes (i.e., microfiltration and ultrafiltration) can offer precise filtration than sand filtration, they pose the problem of reduced efficiency due to membrane fouling. Although many studies have examined membrane fouling by organic substances, there is still not enough data available concerning membrane fouling by inorganic substances. The present research investigated changes in the amounts of inorganic components deposited on the surface of membrane filters over time using membrane specimens sampled thirteen times at arbitrary time intervals during pilot testing in order to determine the mechanism by which irreversible fouling by inorganic substances progresses. The experiments showed that the inorganic components that primarily contribute to irreversible fouling vary as filtration continues. It was discovered that, in the initial stage of operation, the main membrane-fouling substance was iron, whereas the primary membrane-fouling substances when operation finished were manganese, calcium, and silica. The amount of iron accumulated on the membrane increased up to the thirtieth day of operation, after which it reached a steady state. After the accumulation of iron became static, subsequent accumulation of manganese was observed. The fact that the removal rates of these inorganic components also increased gradually shows that the size of the exclusion pores of the membrane filter narrows as operation continues. Studying particle size distributions of inorganic components contained in source water revealed that while many iron particles are approximately the same size as membrane pores, the fraction of manganese particles slightly smaller than the pores in diameter was large. From these results, it is surmised that iron particles approximately the same size as the pores block them soon after the start of operation, and as the membrane pores narrow with the development of fouling, they become further blocked by manganese particles approximately the same size as the narrowed pores. Calcium and silica are assumed to accumulate on the membrane due to their cross-linking action and/or complex formation with organic substances such as humic compounds. The present research is the first to clearly show that the inorganic components that contribute to membrane fouling differ according to the stage of membrane fouling progression; the information obtained by this research should enable chemical cleaning or operational control in accordance with the stage of membrane fouling progression. (C) 2015 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Shin-Ichiro Nishimura, Risho Miyoshi, Asiful Hoque, Taro Miyoshi, Yoshimasa Watanabe
    BIORESOURCE TECHNOLOGY 179 180 - 186 2015年03月 [査読有り][通常論文]
     
    A new approach for the analysis of polysaccharides in membrane bioreactor (MBR) is proposed in this study. Enrichment of polysaccharides by glyco-blotting, in which polysaccharides are specifically collected via interactions between the aldehydes in the polysaccharides and aminooxy groups on glycoblotting beads, enabled MALDI-TOF/MS analysis at a high resolution. Structures of polysaccharides extracted from fouled membranes used in a pilot-scale MBR treating municipal wastewater and those in the supernatant of the mixed liquor suspension in the MBR were investigated. It was found that the overlap between polysaccharides found in the supernatants and those extracted from the fouled membrane was rather limited, suggesting that polysaccharides that dominate in supernatants may not be important in membrane fouling in MBRs. Analysis using a bacterial carbohydrate database suggested that capsular polysaccharides (CPS) and/or lipo-polysaccharides (LPS) produced by gram-negative bacteria are key players in the evolution of membrane fouling in MBRs. (C) 2014 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Rie Ogyu, Taro Miyoshi, Yoshimasa Watanabe
    SEPARATION AND PURIFICATION TECHNOLOGY 142 326 - 331 2015年03月 [査読有り][通常論文]
     
    Evolution of irreversible fouling in pilot-scale membrane bioreactors (MBRs) treating municipal wastewater was studied. Three membrane modules were sacrificed to analyze foulants after they had been used for different durations (1 day, 8 days, 24 days). The module used for 1 day reflected fouling occurring at the initial stage, whereas the module used for 24 days reflected the later stage of fouling. After each module had been used for the predetermined period, it was disassembled and subjected to powerful chemical analysis such as Fourier transform infrared (FTIR) analysis. It was clearly shown that components involved in evolution of irreversible fouling gradually changed depending on the duration. The initial fouling (conditioning of membrane) was caused by humics, whereas later fouling was mainly caused by polysaccharides. A model for evolution of irreversible fouling in MBRs and implications for fouling control are discussed. (C) 2015 Elsevier B.V. All rights reserved.
  • Tokihiro Kurita, Katsuki Kimura, Yoshimasa Watanabe
    SEPARATION AND PURIFICATION TECHNOLOGY 141 207 - 213 2015年02月 [査読有り][通常論文]
     
    A membrane bioreactor (MBR) is not a mainstream wastewater treatment technology, mainly because the energy consumption in an MR operation is high. This study investigated the mitigation of membrane fouling and the reduction in aeration through the introduction of granules into a pilot-scale baffled membrane bioreactor (BMBR) used to treat municipal wastewater. With granular materials, the BMBR could be stably operated, even when the filterability of the mixed liquor suspensions was considerably low due to low temperatures. The aeration rate could be reduced by more than 50% with the help of granules. However, it was found that the introduction of granules damaged parts of the membrane surface. The damage might be avoided by adjusting the contact intensity of the granules and the membrane surface. (C) 2014 Elsevier B.V. All rights reserved.
  • 木村 克輝
    膜 40 6 327 - 331 日本膜学会 2015年 [査読無し]
     
    It is necessary to reduce costs in operation of membrane bioreactors (MBRs) for widespread use of the technology. Aeration used for prevention of attachment of biomass on the membrane surface accounts for the largest portion of the total energy consumption in MBRs and therefore should be focused on. Placing biomass carriers in submerged MBRs has been examined and been reported to be effective in mitigation of membrane fouling. In our bench–scale experiments in which a submerged flat–sheet MBR was operated with cylindrical carriers made from PEG, it was estimated that aeration rate in MBRs could be reduced by 50%. This estimation was verified in a pilot–scale MBR treating municipal wastewater. In that pilot–scale experiment, however, it was found that the carriers introduced caused damages on a part of membrane structures. Observations with a high–speed digital camera revealed that carriers moved much more rapidly in the pilot–scale MBR than in the bench–scale MBR. Also, the carriers moved randomly in the pilot–scale MBR whereas they steadily moved up almost perpendicularly in the bench–scale MBR. These differences in the manner of movement of the carriers in the MBRs seemed to explain the difference in the damage of the membrane in the two MBRs. Modification of aeration in the pilot–scale MBR is likely to avoid the damage on the membrane and is now being examined in our laboratory.
  • Taro Miyoshi, Yuhei Nagai, Tomoyasu Aizawa, Katsuki Kimura, Yoshimasa Watanabe
    WATER SCIENCE AND TECHNOLOGY 72 6 844 - 849 2015年 [査読有り][通常論文]
     
    In this study, the details of proteins causing membrane fouling in membrane bioreactors (MBRs) treating real municipal wastewater were investigated. Two separate pilot-scale MBRs were continuously operated under significantly different operating conditions; one MBR was a submerged type whereas the other was a side-stream type. The submerged and side-stream MBRs were operated for 20 and 10 days, respectively. At the end of continuous operation, the foulants were extracted from the fouled membranes. The proteins contained in the extracted foulants were enriched by using the combination of crude concentration with an ultrafiltration membrane and trichloroacetic acid precipitation, and then separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). The N-terminal amino acid sequencing analysis of the proteins which formed intensive spots on the 2D-PAGE gels allowed us to partially identify one protein (OmpA family protein originated from genus Brevundimonas or Riemerella anatipestifer) from the foulant obtained from the submerged MBR, and two proteins (OprD and OprF originated from genus Pseudomonas) from that obtained from the side-stream MBR. Despite the significant difference in operating conditions of the two MBRs, all proteins identified in this study belong to beta-barrel protein. These findings strongly suggest the importance of beta-barrel proteins in developing membrane fouling in MBRs.
  • K. Kimura, K. Tanaka, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY-WATER SUPPLY 15 2 288 - 293 2015年 [査読有り][通常論文]
     
    A variety of surface waters used for drinking water sources were collected from different parts of Japan to investigate a correlation between the concentration of hydrophilic biopolymer (e.g. proteins and polysaccharides) in the feed water and membrane fouling in microfiltration. Hollow-fiber membranes made from polyvinylidene fluoride with a nominal pore size of 0.1 mu m were used in the series of experiments involving the constant-flow mode of operation with automatic periodical backwashing. Easily available indexes of water quality, such as dissolved organic carbon, UV absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. In contrast, a clear correlation between the concentrations of biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD) and membrane fouling was confirmed in this study. The concentrations of humics exhibited a weak correlation. The impacts of seasonal variation of feed water and coagulant dosage on membrane fouling were also explained well by biopolymer concentrations. Concentrations of biopolymers can be a useful indicator of the fouling potential of feed water in microfiltration.
  • Tokihiro Kurita, Katsuki Kimura, Yoshimasa Watanabe
    JOURNAL OF MEMBRANE SCIENCE 469 292 - 299 2014年11月 [査読有り][通常論文]
     
    Aeration to mitigate membrane fouling accounts for the largest fraction of energy consumed in membrane bioreactors (MBRs). To reduce the energy consumed during MBR operation, alternative methods must be developed to control membrane fouling. Granules should be introduced into submerged MBRs to mitigate membrane fouling due to their mechanical cleaning effect On the membrane surface. This study assessed the possible reduction in aeration for submerged MBRs through introducing granules and investigated membrane fouling characteristics from using granules. Two bench-scale MBRs operated in parallel with synthetic wastewater, and granules were introduced into one MBR. The MBR with granules operated stably even after aeration was reduced by 50%. Reversible fouling was almost entirely controlled through the introduction of granules. However, the granules promoted irreversible fouling due to cake elimination, which acted as a dynamic filter. The overall benefit from granules was apparent; although, reversible fouling dominated in the absence of granules. The foulant characteristics differed with granule use. These characteristic changes were also explained by the absence of the dynamic filtration effect. (C) 2014 Elsevier B.V. All rights reserved.
  • Lutz Boehm, Tokihiro Kurita, Katsuki Kimura, Matthias Kraume
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 65 11 - 23 2014年10月 [査読有り][通常論文]
     
    A phenomenological investigation of single bubbles ascending in a confined geometry with a rectangular cross section was done. Motivated by the goal to get a deeper understanding of the bubble behaviour in flat sheet membrane modules used in membrane bioreactors, the parameters channel depth (=spacing, 5-7 mm), bubble size (3-9 mm), superimposed liquid velocity (0-23.5 cm/s) and rheology of the continuous phase (Newtonian, shear-thinning) were varied. The shear-thinning liquid was used to simulate the rheological behaviour of activated sludge apparent in membrane bioreactors. The analysed properties included the rising paths, bubble shape, absolute and relative terminal rise velocities, friction factors and oscillation frequencies and amplitudes of the bubble. As expected, a significant influence of the rheology of the continuous phase was found on the rising behaviour. In the shear-thinning liquid, the bubbles followed mostly a straight rising path with negligible oscillations. The variation of the channel depth mainly had an influence on the terminal rise velocity of the bubbles ascending in the shear-thinning liquid with higher values in the channel with the larger channel depth. Increasing the bubble size led to higher rising velocities and to enhanced oscillations. (C) 2014 Elsevier Ltd. All rights reserved.
  • Zhiwei Wang, Jinxing Ma, Chuyang Y. Tang, Katsuki Kimura, Qiaoying Wang, Xiaomeng Han
    JOURNAL OF MEMBRANE SCIENCE 468 276 - 307 2014年10月 [査読有り][通常論文]
     
    Membrane bioreactors (MBRs) have been widely used in wastewater treatment and reclamation. Membrane cleaning is an essential part during the operation of MBRs since membrane fouling is an unavoidable problem. In past decades, with the in-depth understanding on membrane fouling, significant advances in membrane cleaning have been achieved. However, a comprehensive review on membrane cleaning in MBRs is still lacking. This paper attempts to critically review the recent developments of membrane cleaning. Firstly, the fouling and cleaning fundamentals are addressed, and then a comprehensive review on physical, chemical, and biological/biochemical cleaning is presented. The procedures of determining proper cleaning protocols for MBR systems are also proposed. Finally, the existing challenges and future research efforts are discussed in order to ensure the development of membrane cleaning toward a more effective and sustainable way in MBRs. (C) 2014 Elsevier B.V. All rights reserved.
  • Hiroshi Yamamura, Katsuki Kimura, Yoshimasa Watanabe
    SEPARATION AND PURIFICATION TECHNOLOGY 132 110 - 114 2014年08月 [査読有り][通常論文]
     
    Water treatment using ultrafiltration (UF) membranes is gaining popularity world-wide, but the problem of membrane fouling needs to be addressed. We investigated the characteristics of membrane foulants by conducting two long-term filtration experiments using surface water from the Chitose River. The membrane was made of polyacrylonitrile and had a molecular weight cut-off of 100 kDa. The experiments were conducted in February 2004 Winter operation (Run 1) and October 2005 Summer operation (Run 2), when feed water characteristics were considerably different. Despite this, rates of physically irreversible fouling were similar. By measuring pure water permeability before and after chemical cleaning, we found that acidic or chelate solutions were most effective for cleaning the membrane from Run 1, whereas an alkaline solution was more effective for that from Run 2. Analysis of the chemical solutions that effective worked for canceling the fouling revealed that acidic cleaning in Run 1 extracted iron, carbohydrate and humic acid, while alkaline cleaning in Run 2 extracted carbohydrates. These results indicates that the iron, carbohydrates and humic acid caused the physically irreversible fouling in Run I, and carbohydrates were mainly responsible in Run 2. Based on the findings obtained in this study, it was suggested that the most important foulants and the most effective chemical cleaning agents may differ substantially between seasons. (C) 2014 Elsevier B.V. All rights reserved.
  • Hiroshi Yamamura, Kenji Okimoto, Katsuki Kimura, Yoshimasa Watanabe
    WATER RESEARCH 54 123 - 136 2014年05月 [査読有り][通常論文]
     
    Although membrane filtration is a promising technology in the field of drinking water treatment, persistent membrane fouling remains a major disadvantage. For more efficient operation, causative agents of membrane fouling need to be identified. Membrane fouling can be classified into physically reversible and irreversible fouling on basis of the removability of the foulants by physical cleaning. Four types of natural organic matter (NOM) in river water used as a source of drinking water were fractionated into hydrophobic and hydrophilic fractions, and their potential to develop irreversible membrane fouling was evaluated by a bench-scale filtration experiment together with spectroscopic and chromatographic analyses. In this study, only dissolved NOM was investigated without consideration of interactions of NOM fractions with particulate matter. Results demonstrated that despite identical total organic carbon (TOC), fouling development trends were significantly different between hydrophilic and hydrophobic fractions. The hydrophobic fractions did not increase membrane resistance, while the hydrophilic fractions caused severe loss of membrane permeability. These results were identical with the case when the calcium was added to hydrophobic and hydrophilic fractions. The largest difference in NOM characteristics between hydrophobic and hydrophilic fractions was the presence or absence of macromolecules; the primary constituent causing irreversible fouling was inferred to be "biopolymers", including carbohydrates and proteins. In addition, the results demonstrated that the extent of irreversible fouling was considerably different depending on the combination of membrane materials and NOM characteristics. Despite identical nominal pore size (0.1 mu m), a polyvinylidene fluoride (PVDF) membrane was found to be more rapidly fouled than a PE membrane. This is probably explained by the generation of strong hydrogen bonding between hydroxyl groups of biopolymers and fluorine of the PVDF membrane. On the basis of these findings, it was suggested that the higher fouling potential of the hydrophilic fraction of the dissolved NOMs from various natural water sources are mainly attributed to macromolecules, or biopolymers. (C) 2014 Elsevier Ltd. All rights reserved.
  • Toshikazu Fukushima, Hiroe Hara-Yamamura, Makoto Urai, Ikuro Kasuga, Futoshi Kurisu, Taro Miyoshi, Katsuki Kimura, Yoshimasa Watanabe, Satoshi Okabe
    WATER RESEARCH 52 73 - 82 2014年04月 [査読有り][通常論文]
     
    Effects of chlorination on the toxicity of wastewater effluents treated by activated sludge (AS) and submerged membrane bioreactor (S-MBRB) systems to HepG2 human hepatoblastoma cells were investigated. In addition to the cytotoxicity and genotoxicity assays, the DNA microarray-based transcriptome analysis was performed to evaluate the change in types of biological impacts on HepG2 cells of the effluents by chlorination. Effluent organic matter (EfOM) and disinfection by-products (DBPs) were also characterized by using Fourier transform mass spectrometry (FT-MS). Although no significant induction of genotoxicity was observed by chlorination for both effluents, the chlorination elevated the cytotoxicity of AS effluent but reduced that of S-MBRB effluent. The FT-MS analyses revealed that more DBPs including nitrogenated DBPs (N-DBPs) were formed in the AS effluent than in the S-MBRB effluent by chlorination, supporting the increased cytotoxicity of AS effluent. The lower O/C ratio of S-MBRB EfOM suggests that a large number of organic molecules were detoxified by chlorination, which consequently decreased the cytotoxicity of S-MBRB effluent. Integration of all the results highlights that both cytotoxicity and biological impacts of chlorinated wastewater effluents were clearly dependent on the EfOM characteristics such as DBPs and O/C ratio, namely, on types of treatment systems. (C) 2014 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Ken Tanaka, Yoshimasa Watanabe
    WATER RESEARCH 49 434 - 443 2014年02月 [査読有り][通常論文]
     
    Although low-pressure membranes (microfiltration (MF) or ultrafiltration (UF)) have become viable options for drinking water treatment, problems caused by membrane fouling must still be addressed. The objective of this study was to compare five different surface waters and to identify a relevant index of water quality that can be used for prediction of the fouling potential of the water. Bench-scale filtration tests were carried out with commercially available hollow-fiber MF membranes. Fairly long-term (a few days) filtrations in the constant-flow mode were carried out with automatic backwash. Membrane fouling in this study was shown to be irreversible as a result of the periodic backwash carried out throughout of the operation. Easily accessible indexes of water quality including dissolved organic carbon (Doc), uv absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. Fluorescence excitation-emission matrix (EEM) could provide information on the presence of protein-like substances in water, and peaks for protein showed some correlation with the membrane fouling. Biopolymer (characterized by high molecular weights and insensitivity to UV light absorption) concentrations in the five waters determined by liquid chromatography with organic carbon detection (LC-OCD) exhibited an excellent correlation with the fouling rates. Coagulation with polyaluminum chloride could mitigate membrane fouling in all cases. The extent of fouling seen with coagulated waters was also correlated with biopolymer concentrations. The relationship between biopolymer concentrations and the fouling rates established for the raw waters could also be applied to the coagulated waters. These results suggested that the contribution of biopolymers to membrane fouling in the present study was significant, an observation that was supported by the analysis of foulants extracted at the termination of each test. Biopolymer concentrations determined by LC-OCD might be used as a key indicator of fouling potential of water for low-pressure membranes. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroe Hara-Yamamura, Koji Nakashima, Asiful Hoque, Taro Miyoshi, Katsuki Kimura, Yoshimasa Watanabe, Satoshi Okabe
    Environmental Science and Technology 47 10 5425 - 5432 2013年05月21日 [査読有り][通常論文]
     
    DNA microarray-based transcriptome analysis with human hepatoma HepG2 cells was applied to evaluate the impacts of whole wastewater effluents from the membrane bioreactors (MBRs) and the activated sludge process (AS). In addition, the conventional bioassays (i.e., cytotoxicity tests and bioluminescence inhibition test), which were well-established for the evaluation of the overall effluent toxicity, were also performed for the same samples. Transcriptome analysis revealed that 2 to 926 genes, which were categorized to 0 to 225 biological processes, were differentially expressed after exposure to the effluents and the raw wastewater. Among the tested effluents, the effluent from a MBR operated at a relatively long solid retention time (i.e., 40 days) and small membrane pore size (i.e., 0.03 μm) showed the least impacts on the HepG2 even at the level comparable to tap water. The observed gene expression responses were in good agreement with the results of cytotoxicity tests, and provided additional molecular mechanistic information on adverse effects occurred in the sublethal region. Furthermore, the genes related to "lipid metabolism", "response to endogenous stimulus", and "response to inorganic substance" were selected as potential genetic markers, and their expression levels were quantified to evaluate the cellular impacts and treatability of wastewater effluents. Although the harmful impacts and innocuous impacts could not be distinguished at present, the results demonstrated that the DNA microarray-based transcriptome analysis with human HepG2 cells was a powerful tool to rapidly and comprehensively evaluate impacts of whole wastewater effluents. © 2013 American Chemical Society.
  • Shaik Khaja Lateef, Bing Zheng Soh, Katsuki Kimura
    Bioresource Technology 150 149 - 155 2013年 [査読有り][通常論文]
     
    Direct membrane filtration (DMF) of municipal wastewater using a microfiltration membrane was investigated to capture organic matter. In contrast to the expectation that membrane fouling cannot be controlled in DMF of domestic wastewater, it was possible to stably continue membrane filtration with relatively high membrane fluxes (~20. LMH) for > 200. h by applying chemically enhanced backwash (CEB), whereas approximately 75% of the organic matter in wastewater could be recovered. Off-line chemical membrane cleaning could completely restore membrane permeability, indicating the possibility of a much longer operation of DMF. Selection of chemical reagents used for CEB was found to influence the amount of organic matter recovered by DMF. Based on the experimental results, feasibility of DMF was discussed by a comparison with a conventional wastewater treatment plant treating the same wastewater as studied in this study. © 2013 The Authors.
  • Katsuki Kimura, Naoko Ogawa, Yoshimasa Watanabe
    Water Science and Technology 67 9 1994 - 1999 2013年 [査読有り][通常論文]
     
    Decline in the permeability in nanofiltration (NF)/reverse osmosis (RO) membranes that filtered effluents from a membrane bioreactor (MBR) treating municipal wastewater was investigated in this study. Four different 2-inch spiral-wound NF/RO membrane elements were continuously operated for 40 days. The results showed that the amount of deposits on the membrane surface did not affect the degree of permeability decline. Laboratory-scale filtration tests with coupons obtained from the fouled membranes also revealed that the contribution of the gel/cake layer to total filtration resistance was minor. Rather, constituents that were strongly bound to the membranes were mainly responsible for permeability decline. Chemical cleaning of the fouled membranes carried out after removal of the cake showed that silica played an important role in the decline in permeability. A considerable amount of organic matter which was mainly composed of carbohydrates and proteins was also desorbed from the fouled membranes. © IWA Publishing 2013.
  • K. Kimura, R. Ogyu, T. Miyoshi, T. Naruse, T. Tsuyuhara, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY 67 11 2602 - 2607 2013年 [査読有り][通常論文]
     
    Membrane fouling needs to be mitigated for widespread use of membrane bioreactors (MBRs). It has been pointed out that particles with small sizes found in supernatants (sub-micron particles) of mixed liquor suspensions of MBRs are important in the evolution of membrane fouling of this technology. However, information on characteristics of sub-micron particles in MBRs is still insufficient. In this study, a pilot-scale MBR treating municipal wastewater was used to investigate and characterize sub-micron particles in an MBR and to identify the size fraction(s) responsible for irreversible fouling in an MBR. It was clearly shown that characteristics of sub-micron particles in the MBR varied considerably depending on their sizes. Results of Fourier transform infrared (FTIR) analysis and monosaccharide analysis suggested that irreversible fouling in this study was mainly caused by the specific size fraction of 0.1-0.45 mu m, which was close to the size of micropores of the membrane used. Pore plugging might explain this to some extent.
  • Katsuki Kimura, Ippei Tanaka, Shin-Ichiro Nishimura, Risho Miyoshi, Taro Miyoshi, Yoshimasa Watanabe
    WATER RESEARCH 46 17 5725 - 5734 2012年11月 [査読有り][通常論文]
     
    Membrane fouling remains a major obstacle for wider application of membrane bioreactors (MBRs) to wastewater treatment. Polysaccharides in mixed liquor suspensions in the reactors are thought to be mainly responsible for the evolution of membrane fouling in MBRs. However, details of polysaccharides causing membrane fouling in MBRs are still unknown. In this study, polysaccharides in a mixed liquor suspension of a pilot-scale MBR treating municipal wastewater were fractionated by using lectins, special proteins that bind to specific polysaccharides depending on their properties. Fouling potentials of the fractionated polysaccharides were assessed by bench-scale dead-end filtration tests. It was clearly shown that the degrees of fouling caused by fractionated polysaccharides were significantly different. The amounts of polysaccharides in each fraction could not explain the variations in the fouling, indicating the presence of polysaccharides with high specific fouling potentials. To investigate structures and origins of the polysaccharides with high fouling potentials, matrix-assisted laser desorption/ionization (MALDI)-time of flight (TOF)/mass spectrometry (MS) analysis was applied to the fractionated polysaccharides after partial hydrolysis. Several mass peaks obtained could be assigned to fragments of structures of polysaccharides (i.e., oligosaccharides) reported in a database/literature. This is the first report showing the plausible structures of polysaccharides in MBRs based on MS. A deeper understanding and effective control of membrane fouling in MBRs could be achieved with information obtained by the approach used in this study. (C) 2012 Elsevier Ltd. All rights reserved.
  • Taro Miyoshi, Tomoyasu Aizawa, Katsuki Kimura, Yoshimasa Watanabe
    INTERNATIONAL BIODETERIORATION & BIODEGRADATION 75 15 - 22 2012年11月 [査読有り][通常論文]
     
    The proteins that caused membrane fouling in a continuous operation of membrane bioreactors (MBRs) treating real municipal wastewater were investigated in detail. We continuously operated two identical pilot-scale MBRs under different solid retention times (SRTs) and extracted the foulants at the end of the operation. Regardless of the operating conditions, proteins were dominant components in the foulants extracted from the fouled membranes. The extracted proteins were subjected to the separation with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and the identification through the N-terminal amino acid sequencing analysis. The proteins concentrated by the combination of the crude concentration using an ultra-filtration (UF) membrane and trichloroacetic acid (TCA) precipitation were separated and visualized well on 2D-PAGE gels. The results of 2D-PAGE analysis indicated that the compositions of proteins that caused membrane fouling significantly differed depending on the SRT, although such differences cannot be seen in the amino acid composition analysis. Analyzing selected 2D-PAGE spots by N-terminal amino acid sequencing analysis led to the identification of two well-characterized outer membrane proteins originating from Pseudomonas genus, namely OprF and OprD. To our knowledge, this is the first successful identification of proteins that have caused membrane fouling in continuous operations of MBRs treating real wastewater. (C) 2012 Elsevier Ltd. All rights reserved.
  • 木村 克輝
    膜 37 5 230 - 234 THE MEMBRANE SOCIETY OF JAPAN 2012年09月01日 [査読無し]
     
    Application of membrane technology to water purification and wastewater treatment is being accelerated. The main obstacle for wider use of membrane technology is membrane fouling, which can be divided into two types depending on its reversibility: reversible (mostly cake layer) fouling and irreversible fouling. The former type of fouling can be cancelled by physical cleaning such as backwashing or air-souring, whereas the latter needs chemical cleaning to be cancelled. Most of full-scale membrane filtration units are operated with routine physical cleaning and control of irreversible fouling is therefore important. We have focused on characteristics of foulants causing irreversible fouling in membrane processes and have conducted many pilot-scale experiments using real drinking water source and municipal wastewater. Foulants extracted from the fouled membranes were subject to various analysis to investigate the characteristics of foulants. Analysis using Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (NMR) spectrum revealed that foulants that were responsible for irreversible fouling were mainly composed of polysaccharides and proteins regardless of type of application. It was also found that monosaccharide composition and amino acid composition in the foulants significantly varied depending on operational conditions of membrane processes. Detailed information on the foulants that cause irreversible fouling including their structures and origins is being revealed by advanced analytical techniques such as MALDI-TOF/MS. Once the structures of the foulants have been fully identified, it will be possible to specifically monitor the important foulants or microorganisms that produce them, which might enable effective control of membrane fouling. Also, extensive investigation of interactions between the important foulants and various membrane materials/structures should lead to the development of new anti-fouling membranes.
  • Asiful Hoque, Katsuki Kimura, Taro Miyoshi, Nobuhiro Yamato, Yoshimasa Watanabe
    SEPARATION AND PURIFICATION TECHNOLOGY 93 83 - 91 2012年06月 [査読有り][通常論文]
     
    Membrane bioreactors (MBRs) have become very attractive during the past decade owing to their advantages, although MBR operation has not been optimized yet. Recently, air-sparged side-stream MBRs (ASMBRs) have received much attention because they can overcome the drawbacks of submerged MBRs such as the difficulty of cleaning membrane modules. Widespread application of MBRs has been limited by problems associated with membrane fouling, and ASMBRs are not exceptions. Hydraulic conditions on the membrane surface used in an ASMBR are different from those in a submerged MBR, and this difference affects the characteristics of foulants. The aim of this study was to determine foulant characteristics in a pilot-scale ASMBR operated at an existing municipal wastewater treatment plant. Cylindrical membrane modules holding about 100 membrane tubes each were installed vertically in the ASMBR. Differences of foulants depending on tube positions in the horizontal cross section were investigated in the first experiment. There were no significant differences in the foulant characteristics regardless of the tube positions in the membrane module. This first experiment also showed that humic substances were dominant in the foulants extracted from the tubular membranes used in the ASMBR, whereas hydrophilic substances such as polysaccharides/proteins were reportedly dominant in foulants in the case of submerged MBRs. In the following experiment, a tiny hollow-fiber membrane module was submerged in the ASMBR's reaction tank to filter the shared biomass suspension and enable direct comparison of foulant characteristics in different MBR configurations (i.e., air-sparged side-stream versus submerged). Humic substances were again found to be dominant in foulants extracted from the ASMBR's tubular membranes, whereas hydrophilic organic matter was dominant in foulants extracted from the submerged hollow-fiber membranes. We hypothesize that different hydraulic conditions in the two configurations brought about the difference in foulants. The results obtained in this study suggest that effective measures to address membrane fouling will differ depending on the MBR configuration. (C) 2012 Elsevier B.V. All rights reserved.
  • A. Hoque, T. Miyoshi, K. Kimura, Y. Watanabe
    SEPARATION SCIENCE AND TECHNOLOGY 47 10 1455 - 1463 2012年 [査読有り][通常論文]
     
    We conducted a high-load operation of a baffled bio-reactor equipped with air-sparged side-stream tubular membrane modules for treating actual municipal wastewater at two different periods (high-and low-temperature). Although nitrogen removal efficiency slightly decreased at the low-temperature period, this baffled bio-reactor showed excellent nitrogen and phosphorus removal efficiencies. We also investigated the developments of both physically reversible and irreversible fouling during operation with two-phase flow (mixed-liquor and gas) at various gas velocities and the mixed-liquor velocity was fixed at 0.50 m/s. The membrane flux was fixed at 80 L/m(2)/hour throughout the experiments. Regardless of the difference in temperature, the trends in the development of these two types of membrane fouling caused by the difference in gas velocity were similar. For physically reversible fouling, an optimum gas velocity, in which the development of this type of fouling was minimized, was found to be around 0.42 m/s (corresponding void fraction was 0.45). A further increase in gas velocity resulted in more reversible fouling. On the other hand, the degree of physically irreversible fouling decreased as gas velocity increased. The results obtained in this study indicated the effect of gas velocity on fouling control differs depending on the type of membrane fouling.
  • Taro Miyoshi, Tomoyasu Aizawa, Katsuki Kimura, Yoshimasa Watanabe
    DESALINATION AND WATER TREATMENT 34 1-3 150 - 155 2011年10月 [査読無し][通常論文]
     
    We investigated the relationship between the nature of proteins and their fouling propensities in pilot-scale membrane bioreactors (MBRs) treating real municipal wastewater with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). In 2D-PAGE, proteins are separated based on their isoelectric points and molecular weights, and therefore, information can be obtained on the nature of the proteins. Foulants extracted from fouled membranes at the end of continuous operation and organic matter contained in mixed liquor suspension were analyzed by 2D-PAGE, and the results were compared. This analysis was performed for two identical MBRs operated under different solid retention times (SRT) to investigate the effect of the operating condition on the types of proteins with high fouling propensities. In the MBR operated with a long SRT, the presence of proteins that appeared in the neutral pH range was more pronounced in the extracted foulant. Because the pH of the mixed liquor suspension was in the range of 6-7 throughout the continuous operation, the difference in protein profiles between the extracted foulant and the organic matter contained in the mixed liquor suspension in the MBR operated with a long SRT can be explained by a decrease in solubility of a protein at its isoelectric point. In contrast, in the MBR operated with a short SRT, the presence of proteins that appeared in the acidic region (pH 3-5) was more prominent in the extracted foulant compared with the organic matter contained in the mixed liquor suspension. The results obtained in this study imply that dominant fouling mechanisms differed depending on the operating condition.
  • Taro Miyoshi, Tomoyasu Aizawa, Katsuki Kimura, Yoshimasa Watanabe
    DESALINATION AND WATER TREATMENT 34 1-3 150 - 155 2011年10月 [査読有り][通常論文]
     
    We investigated the relationship between the nature of proteins and their fouling propensities in pilot-scale membrane bioreactors (MBRs) treating real municipal wastewater with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). In 2D-PAGE, proteins are separated based on their isoelectric points and molecular weights, and therefore, information can be obtained on the nature of the proteins. Foulants extracted from fouled membranes at the end of continuous operation and organic matter contained in mixed liquor suspension were analyzed by 2D-PAGE, and the results were compared. This analysis was performed for two identical MBRs operated under different solid retention times (SRT) to investigate the effect of the operating condition on the types of proteins with high fouling propensities. In the MBR operated with a long SRT, the presence of proteins that appeared in the neutral pH range was more pronounced in the extracted foulant. Because the pH of the mixed liquor suspension was in the range of 6-7 throughout the continuous operation, the difference in protein profiles between the extracted foulant and the organic matter contained in the mixed liquor suspension in the MBR operated with a long SRT can be explained by a decrease in solubility of a protein at its isoelectric point. In contrast, in the MBR operated with a short SRT, the presence of proteins that appeared in the acidic region (pH 3-5) was more prominent in the extracted foulant compared with the organic matter contained in the mixed liquor suspension. The results obtained in this study imply that dominant fouling mechanisms differed depending on the operating condition.
  • Taro Miyoshi, Tomoyasu Aizawa, Katsuki Kimura, Yoshimasa Watanabe
    Desalination and Water Treatment 34 150 - 155 2011年01月 [査読有り][通常論文]
     
    We investigated the relationship between the nature of proteins and their fouling propensities in pilot-scale membrane bioreactors (MBRs) treating real municipal wastewater with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). In 2D-PAGE, proteins are separated based on their isoelectric points and molecular weights, and therefore, information can be obtained on the nature of the proteins. Foulants extracted from fouled membranes at the end of continuous operation and organic matter contained in mixed liquor suspension were analyzed by 2D-PAGE, and the results were compared. This analysis was performed for two identical MBRs operated under different solid retention times (SRT) to investigate the effect of the operating condition on the types of proteins with high fouling propensities. In the MBR operated with a long SRT, the presence of proteins that appeared in the neutral pH range was more pronounced in the extracted foulant. Because the pH of the mixed liquor suspension was in the range of 6-7 throughout the continuous operation, the difference in protein profiles between the extracted foulant and the organic matter contained in the mixed liquor suspension in the MBR operated with a long SRT can be explained by a decrease in solubility of a protein at its isoelectric point. In contrast, in the MBR operated with a short SRT, the presence of proteins that appeared in the acidic region (pH 3-5) was more prominent in the extracted foulant compared with the organic matter contained in the mixed liquor suspension. The results obtained in this study imply that dominant fouling mechanisms differed depending on the operating condition. © 2011 Desalination Publications. All rights reserved.
  • Naoko Ogawa, Katsuki Kimura, Yoshimasa Watanabe
    DESALINATION AND WATER TREATMENT 18 1-3 292 - 296 2010年06月 [査読有り][通常論文]
     
    Securing a new water resource is becoming an important issue as severe shortage of water is seen throughout the world. Reuse of highly treated wastewater can be a viable option to address this issue. In this study, an advanced wastewater treatment system comprised of a membrane bioreactor followed by nanofiltration (NF) and reverse osmosis (RO) membranes was examined at pilot-scale with real wastewater. Treatment performance of the system was evaluated on the basis of 40 days continuous operation. At the end of the operation, membrane fouling in NF/RO membranes was investigated by disassembling the membrane modules. Although there was no significant difference in water qualities of the permeates between the NF and the RO membranes, membrane fouling was more significant in the NF membrane than in the RO membrane. After disassembling the membrane modules, a portion of the fouled membranes was cleaned stepwise and pure water permeabilities of the membrane specimen at each cleaning step were determined with a bench-scale cross-flow filtration unit. It was revealed that contribution of the cake/gel layers to the total filtration resistance was limited in both NF and RO membranes. It was found that inorganic matter, particularly silica, was main foulant in the NF membrane whereas organic matter mainly caused fouling in the RO membrane.
  • Stefan Panglisch, Katsuki Kimura, Gary Amy
    Journal of Water Supply: Research and Technology - AQUA 59 2-3 79 - 80 2010年 [査読無し][通常論文]
  • T. Tsuyuhara, Y. Hanamoto, T. Miyoshi, K. Kimura, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY 61 9 2235 - 2240 2010年 [査読有り][通常論文]
     
    This study aimed to examine the impact of membrane properties on membrane fouling in membrane bioreactor (MBR). Membrane fouling was divided into two categories: physically reversible and irreversible fouling. Membrane properties related to each type of membrane fouling were investigated separately. Five microfiltration (MF) and one ultrafiltration (UF) membranes with different properties (pore size, contact angle, roughness, zeta potential, and pure water permeability) were examined with a laboratory-scale MBR, fed with synthetic wastewater. Two separate experiments were conducted: the first to examine physically reversible fouling, and the second to examine physically irreversible fouling. The correlation between the degree of each type of fouling and membrane properties was studied. High correlation was observed between the degree of physically reversible fouling and roughness (R(2) = 0.96). In contrast, with regard to physically irreversible fouling, strong correlation between roughness and degree of membrane fouling can only be found in the case of MF membranes. Except for the membrane with the highest roughness, the degree of physically irreversible fouling can be well correlated with pure water permeability (lower pure water permeability results in higher degree of physically irreversible fouling) including UF membrane. On the basis of the results obtained in this study, it can be concluded that roughness is an important factor in determination of physically reversible fouling regardless of the types of membrane (i.e. MF or UF membranes) and evolutions of physically irreversible fouling can be mitigated when an MBR is operated with membranes with smooth surface and high pure water permeability.
  • T. Miyoshi, I. Tanaka, T. Tsuyuhara, E. Watanabe, T. Aizawa, K. Kimura, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY 61 7 1787 - 1792 2010年 [査読有り][通常論文]
     
    In this study, the fouling potentials of polysaccharides contained in mixed liquor suspension in a membrane bioreactor (MBR) treating municipal wastewater were investigated using lectin affinity chromatography. This investigation was carried out with different membranes to assess the effects of membrane materials on fouling potentials of polysaccharides. In lectin affinity chromatography, some polysaccharides with high affinity to the lectin in the column can be retained in the column. The fouling potentials of the retained polysaccharides were evaluated by dead-end filtration test. Degree of reduction in fouling potential differed considerably when different lectins were used in affinity chromatography indicating that fouling potentials of polysaccharide differed depending on types of polysaccharide. Trends in the reduction of fouling potential were different depending on membrane materials. Characteristics of the organic matter associated with polysaccharides removed by lectins were investigated by means of excitation-emission matrices (EEM). The results of EEM analysis indicate that the characteristics of the organic matter eluted from different lectins were different as long as elution reagents for the lectin were different. Characteristics of the organic matter eluted from the lectins which have the same elution reagent were similar in terms of shapes of EEM fluorescence spectra. However, the trends in reduction of fouling potentials could not be explained by the characteristics of organic matter assessed by EEM analysis. On the basis of the results obtained in this study, it can be concluded that characteristics of membrane and structures or properties of sugar chain would play an important role in determining fouling potentials.
  • K. Kimura, H. Hara, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY 62 5 1084 - 1089 2010年 [査読有り][通常論文]
     
    Lab-scale batch experiments with biosolids collected from a full-scale activated sludge system (AS) and a pilot-scale membrane bioreactor (MBR) were carried out to investigate the mechanisms of elimination of 5 acidic pharmaceuticals and 2 neutral pharmaceuticals. Batch elimination experiments were conducted under the conditions of pH of 6 and 7, and a great impact of pH on elimination of pharmaceuticals was shown by the significant differences in elimination rates under different pH conditions: elimination of pharmaceuticals was enhanced under the condition of lower pH regardless of the type of biosolid. Degree of mineralization of ibuprofen was also investigated in this study by using (14)C-labeled compounds. Although ibuprofen has been considered to be a readily biodegradable pharmaceutical in previous studies, the results obtained in this study demonstrated that the degree of mineralization of ibuprofen would be limited in biological wastewater treatment including MBRs. The results obtained in this study imply that a large portion of pharmaceuticals that have been considered "biodegradable", such as ibuprofen, entering into wastewater treatment plants will eventually be discharged into natural water bodies as intermediates, although concentrations of them may look reduced on the basis of common analytical methods (i.e. GC/MS or LC/MS/MS).
  • Taro Miyoshi, Tomoo Tsuyuhara, Rie Ogyu, Katsuki Kimura, Yoshimasa Watanabe
    WATER RESEARCH 43 20 5109 - 5118 2009年12月 [査読有り][通常論文]
     
    We investigated seasonal variation in membrane fouling in membrane bioreactors (MBRs) treating municipal wastewater regarding the difference between physically reversible and irreversible fouling. Two separate MBRs with different solid retention times (SRTs) operated in parallel for about 200 days including high-and low-temperature periods to evaluate the effect of operating conditions on seasonal variation of membrane fouling. Seasonal variations of both types of membrane fouling (i.e., physically reversible and irreversible fouling) were observed for the MBR with short SRT (13 days). However, in the MBR with long SRT (50 days), there were no significant seasonal variations in both types of membrane fouling. In the MBR with short SRT, the trends in the seasonal variation in the development rates of physically reversible and irreversible fouling were different. Physically reversible fouling was more significant in the low-temperature period, while physically irreversible fouling developed more rapidly in the high-temperature period. The development rates of physically reversible fouling can be related to the concentration of dissolved organic matter in the mixed liquor suspension of MBRs; whereas those of physically irreversible fouling could not be explained by the concentration of dissolved organic matter. The characteristics of dissolved organic matter differed depending on the temperature period, and the trends of dissolved organic matter variation in mixed liquor were similar with those of foulants that caused physically irreversible fouling. The results obtained in this study indicated that seasonal variation in physically reversible and irreversible fouling is related to changes in quantity and quality of organic matter, respectively. (C) 2009 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Tomonori Iwase, Shusuke Kita, Yoshimasa Watanabe
    WATER RESEARCH 43 15 3751 - 3758 2009年08月 [査読有り][通常論文]
     
    Increasing attention has been given to pollution of the water environment by pharmaceutical compounds discharged from wastewater treatment plants. High-pressure driven membranes such as a nanofiltration (NF) membrane and a reverse osmosis (RO) membrane are considered to be effective for control of pharmaceuticals in wastewater treatment. In practical applications of NF/RO membranes to municipal wastewater treatment, feed water for the membranes always contains organic macromolecules at concentrations of up to 10 mg-TOC/L, which are mainly composed of soluble microbial products (SMPs) produced during biological wastewater treatment such as an activated sludge process. In this study, influence of these organic macromolecules on removal of six pharmaceuticals by NF/RO membranes (UTC-60 and LF10) was investigated. Two types of biological treatment (conventional activated sludge process followed by media filtration (i.e., tertiary treatment) and treatment with a membrane bioreactor (MBR)) were examined as pretreatments for NF/RO membranes in this study. In the filtration tests with wastewater effluents, removal of the pharmaceuticals was higher than that seen with deionized pure water spiked with the pharmaceuticals. The increase was significant in the case of the NF membrane. Both alteration of membrane surface properties due to membrane fouling and association of the pharmaceuticals with organic macromolecules contributed to the increase in removal of pharmaceuticals by the membranes. Characteristics of the organic macromolecules contained in the wastewater effluents differed depending on the type of treatment, implying that removal of pharmaceuticals by NF/RO membranes is influenced by the type of pretreatment employed. (C) 2009 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Takuro Naruse, Yoshimasa Watanabe
    WATER RESEARCH 43 4 1033 - 1039 2009年03月 [査読有り][通常論文]
     
    A membrane bioreactor (MBR) is a promising wastewater treatment technology, but there is a need for efficient control of membrane fouling, which increases operational and maintenance costs. Soluble microbial products (SMP) have been reported to act as major foulants; in the operation of MBRs used for wastewater treatment. In this study, SMP in MBRs operated with different sludge retention times (SRTs) were investigated by means of various analytical techniques and their relations to the evolution of membrane fouling were considered. Bench-scale filtration experiments were carried out in a laboratory with synthetic wastewater to eliminate fluctuations that would occur with the use of real wastewater and that would lead to fluctuations in compositions of SMP. Three identical submerged MBRs were operated for about 50 days under the same conditions except for SRT (17, 51 and 102 days). Accumulation of SMP in the MBRs estimated by conventional analytical methods (i.e., the phenol-sulfuric acid method and the Lowry method) was significant in the cases of short SRTs. However, the degrees of membrane fouling in the MBRs were not directly related to the concentrations of SMP in the reactors estimated by the conventional analytical methods. Non-conventional analytical methods such as excitation-emission matrix (EEM) fluorescence spectroscopy revealed that characteristics of SMP in the three reactors considerably differed depending on SRT. Foulants were extracted from the fouled membranes at the end of the operation and were compared with SMP in each MBR. It was clearly shown that characteristics of the foulants were different depending on SRT, and similarities between SMP and the extracted foulants were recognized in each MBR on the basis of results of EEM measurements. However, such similarities were not found on the basis of results obtained by using the conventional methods for analysis of SMP. The results of this study suggest that the use of conventional methods for analysis of SMP is not appropriate for investigation of membrane fouling in MBRs. (C) 2008 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Taro Miyoshi, Takuro Naruse, Nobuhiro Yamato, Rie Ogyu, Yoshimasa Watanabe
    DESALINATION 231 1-3 268 - 275 2008年10月 [査読有り][通常論文]
     
    The main obstacle for a wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling, which increases operating costs. Fora more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. We conducted two separate pilot-scale experiments using real municipal wastewater to investigate the influence of the membrane flux in MBRs on the characteristics of foulants, which were analyzed by Fourier transform infrared (FTIR) spectra, (13)C nuclear magnetic resonance (NMR) spectra, monosaccharide composition and amino acid analyses. In each experiment, two identical membrane modules were submerged in the same MBR tank and were operated under different membrane fluxes. The results obtained in this study indicated that the membrane filtration flux significantly influenced membrane fouling in MBRs. Membrane fouling in the module operated with the higher flux was much greater than that of the other on the basis of the volume of filtered mixed liquor suspension. Analyses of the foulants desorbed from the fouled membranes revealed that the nature of the foulants significantly differed depending on the membrane flux despite the fact that the two modules filtered the same mixed liquor suspension at the same time. The difference in characteristics of the foulants caused by the difference in the membrane flux was similar in the two separate experiments, indicating that reproducibility of the data was sufficient. It was thought that different fractions of the mixed liquor suspension were transported to the surfaces of the membranes depending on the membrane flux and subsequently caused membrane fouling to different extents. The foulant desorbed from the membrane operated with a higher flux seemed to cause severer fouling than the foulant desorbed from the other membrane.
  • Hiroshi Yamamura, Katsuki Kimura, Takaharu Okajima, Hiroshi Tokumoto, Yoshimasa Watanabe
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 42 14 5310 - 5315 2008年07月 [査読有り][通常論文]
     
    Fouling in membranes used for water treatment has been attributed to the presence of natural organic matter (NOM) in water. There have been reports recently on the contribution of hydrophilic fractions of NOM(e.g., carbohydrate-like substances) to fouling, but there is still little information about the physicochemical interactions between membranes and carbohydrate-like substances. In this study, the affinity of carbohydrate-like substances to two different microfiltration (MF) membranes was investigated by using atomic force microscopy (AFM) and functionally modified microspheres. Microspheres were attached to the tip of the cantilever in an AFM apparatus and the adhesion forces working between the microspheres and the membranes were determined. The microspheres used in this study were coated with either hydroxyl groups or carboxyl groups to be used as surrogates of carbohydrate-like substances or humic acid, respectively. Measurements of adhesion force were carried out at pH of 6.8 and the experimental results demonstrated that the adhesion force to membranes was strong in the case of hydroxyl groups but weak in the case of carboxyl groups. The strong adhesion between the hydroxyl group and the membrane surface is explained by the strong hydrogen bond generated. It was also found that the affinity of the hydroxyl group to a polyvinylidenefluoride (PVDF) membrane was much higher than that to a polyethylene (PE) membrane, possibly due to the high electronegative nature of the PVDF polymer. The time course of changes in the affinity of hydroxyl group to a membrane used in a practical condition was investigated by repeatedly carrying out AFM force measurements with PE membrane specimens sampled from a pilot plant operated at an existing water treatment plant. Microspheres exhibited strong affinity to the membrane at the initial stage of operation (within 5 days), but subsequently exponential reduction of the affinity was seen until the end of operation, as a result of fouling development. However, the magnitude of affinity of hydroxyl-modified microspheres was much higher than that of carboxyl-modified microspheres even after the significant reduction of affinity of hydroxyl-modified microspheres to the membranes was seen. The results obtained in this study partially explain why hydrophilic NOM dominated over humic substances in foulants of membranes used for water treatment in recent studies on fouling.
  • Katsuki Kimura, Tomohiro Maeda, Hiroshi Yamamura, Yoshimasa Watanabe
    JOURNAL OF MEMBRANE SCIENCE 320 1-2 356 - 362 2008年07月 [査読有り][通常論文]
     
    Chemical coagulation has been widely used as a method to mitigate membrane fouling in MF/UF membranes used for drinking water treatment. Optimization of coagulation as pre-treatment of membrane processes has not been achieved yet: the optimum condition of coagulation for conventional treatment systems is not necessarily applicable to membrane-based treatment systems. This study investigated (physically) irreversible membrane fouling in an MF membrane used with pre-coagulation by aluminum salt. In a series of bench-scale filtration tests, feed water containing commercially available humic acid or organic matter isolated from surface water was coagulated with polyaluminum chloride (PACl) under various conditions and subsequently filtered with an MF membrane with the nominal pore size of 0.1 mu m. It was found that coagulation conditions had great impacts on the degree of physically irreversible fouling. Acidic conditions improved the quality of treated water but generally caused greater physically irreversible fouling than did neutral or alkaline conditions. Also, dosage of coagulant was found to be influential on the degree of membrane fouling: high dosage of coagulant frequently caused more severe irreversible fouling. Sizes of flocs seemed to become small under acidic conditions in this study, which was indicated by high concentrations of aluminum in the permeate under acidic conditions. It is thought that small flocs produced under acidic conditions could migrate into micropores of the membrane and caused physically irreversible fouling by plugging or adsorption. These findings obtained in the bench-scale tests were verified in a long-term pilot-scale test. (C) 2008 Elsevier B.V. All rights reserved.
  • Katsuki Kimura, Rie Nishisako, Taro Miyoshi, Ryusuke Shimada, Yoshimasa Watanabe
    WATER RESEARCH 42 3 625 - 632 2008年02月 [査読有り][通常論文]
     
    Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance. (c) 2007 Elsevier Ltd. All rights reserved.
  • Hiroshi Yamamura, Katsuki Kimura, Yoshimasa Watanabe
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 41 19 6789 - 6794 2007年10月 [査読有り][通常論文]
     
    Control of membrane fouling is important for more efficient use of membranes in water treatment. Control of physically irreversible fouling, which is defined as fouling that requires chemical cleaning to be cancelled, is particularly important for reduction of operation cost in a membrane process. In this study, a long-term filtration experiment using three different types of MF and UF membranes was carried out at an existing water purification plant, and the evolution of physically irreversible fouling was investigated. The experimental results demonstrated that the extent of physically irreversible fouling differed significantly depending on the membrane type. Cleaning of the fouled membranes with various chemical reagents demonstrated that organic matter was mainly responsible for physically irreversible fouling. Organic matter that had caused physically irreversible fouling in the long-term operation was desorbed from the fouled membranes and was subjected to Fourier transform infrared and C-13 nuclear magnetic resonance analyses. These analyses revealed that carbohydrates were dominant in the membrane foulant regardless of the type of membrane. Based on measurements of molecular weight distribution of organic matter in the feedwater and the permeates from the membranes, a two-step fouling mechanism is proposed to explain the dominance of carbohydrates in the foulant: hydrophobic (humic-like) components with small molecular weight are first adsorbed on the membrane and, consequently, narrow the size of micro-pores of membranes, and then hydrophilic (carbohydrate-like) compounds with larger molecular weight plug the narrowed pores or the hydrophilic compounds are adsorbed onto the membrane surface conditioned by the hydrophobic components.
  • Hiroshi Yamamura, Kenji Okimoto, Katsuki Kimura, Yoshimasa Watanabe
    JOURNAL OF WATER SUPPLY RESEARCH AND TECHNOLOGY-AQUA 56 6-7 425 - 434 2007年09月 [査読有り][通常論文]
     
    Water treatment using microfiltration (MF)/ultrafiltration (UF) membranes is gaining in popularity all over in this study the influence of problem of membrane fouling needs to be addressed the world but the, calcium on irreversible fouling in MF/UF membrane filtering natural organic matter (NOM) was investigated on the basis of a series of bench-scale filtration tests. Two types of feed water, solution of commercially available humic acid and surface water used for drinking water source, were filtered with four different MF/UF membranes. It was found that the influence of calcium on the evolution of irreversible fouling would differ depending on the feed water characteristics. Calcium facilitated the aggregation of small molecules with hydrophobic nature contained in commercially available humic acid and the aggregate probably plugged the micropores, resulting in severe irreversible fouling. The effect of calcium was not obvious in the case of the surface water used in this study. This result implies that the use of commercial humic acid for the examination of membrane fouling would be inappropriate.
  • Hiroshi Yamamura, Soryong Chae, Katsuki Kimura, Yoshimasa Watanabe
    WATER RESEARCH 41 17 3812 - 3822 2007年09月 [査読有り][通常論文]
     
    The main disadvantage of membrane filtration is membrane fouling, which remains as the major obstacle for more efficient use of this technology. Information about the constituents that cause fouling is indispensable for more efficient operation. We examined the changes in both foulant characteristics and membrane morphology by performing the pilot-scale filtration test using one microfiltration membrane. During the operation, we cut the membrane fibers three times, and the components that caused irreversible fouling were extracted by acid or alkaline solution. We found that the characteristic of inorganic matter extracted by acid solution completely differed depending on the filtration period. A large amount of iron was extracted in the second chemical cleaning, while manganese was the dominant component of the extracted inorganic matter in the third chemical cleaning. The analysis of Fourier transform infrared (FTIR) and cross polarization magic angle spinning carbon-13 (CPMAS C-13) nuclear magnetic resonance (NMR) demonstrated that the contribution of humic substances and carbohydrate in the organic foulant had increased as fouling developed. The changes in the major foulant have no relation with the fluctuation in feed water. The analysis of membrane morphology illustrated that the cake layer started to build up after the blockage of membrane pores. Based on the above results, we hypothesized the following fouling mechanism: the pores were covered or narrowed with relatively large particles such as iron, carbohydrate or protein; small particles such as manganese or humic substances blocked the narrowed pores; and finally an irreversible cake layer started to build up on the membrane surface. (c) 2007 Elsevier Ltd. All rights reserved.
  • Katsuki Kimura, Hiroe Hara, Yoshimasa Watanabe
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 41 10 3708 - 3714 2007年05月 [査読有り][通常論文]
     
    The elimination of six acidic pharmaceuticals (clofibric acid, diclofenac, ibuprofen, ketoprofen, mefenamic acid, and naproxen) in a real wastewater treatment plant (WWTP) using an activated sludge system and membrane bioreactors (MBRs) was investigated by using a gas chromatography/mass spectrometry (GC/MS) system for measurement of the compounds. Limited information is available for some of the tested pharmaceuticals at present. Solid retention times (SRTs) of the WWTP and the two MBRs were 7, 15, and 65 days, respectively. The elimination rates varied from compound to compound. The MBRs exhibited greater elimination rates for the examined pharmaceuticals than did the real plant. Dependency of the elimination rates of the pharmaceuticals on SRTs was obvious; the MBR operated with a longer SRT of 65 days clearly showed better performance than did the MBR with a shorter SRT of 15 days. The difference between the two MBRs was particularly significant in terms of elimination of ketoprofen and diclofenac. Measurements of the amounts of adsorbed pharmaceuticals on the sludge and aerobic batch elimination experiments were carried out to investigate the elimination pathways of the pharmaceuticals. Results of the batch elimination tests revealed that the sludges in the MBRs had large specific sorption capacities mainly due to their large specific surface areas. Despite the sorption capacities of sludges, the main mechanism of elimination of the pharmaceuticals in the investigated processes was found to be biodegradation. Biodegradation of diclofenac, which has been believed to be refractory to biodegradation, seemed to occur very slowly.
  • K. Kimura, M. Enomoto, Y. Watanabe
    WATER SCIENCE AND TECHNOLOGY 55 7 119 - 126 2007年 [査読有り][通常論文]
     
    Submerged membrane bioreactors (MBRs) have been gaining in popularity in various types of wastewater treatment. One drawback of submerged MBRs is difficulty in removing nitrogen as they are accompanied with intensive aeration inside the reactor and therefore principally operated under aerobic conditions. In order to address this problem, a simple modification for submerged MBRs, insertion of baffles to create alternative aerobic/anoxic conditions, was proposed. In this study, the performance of the proposed baffled membrane bioreactor (BMBR) was investigated based on a pilot-scale experiment using a real municipal wastewater. With appropriate operating conditions, the BMBR could remove more than 70% of total nitrogen contained in the feed water without any external carbon source. The BMBR demonstrated a good treatment performance in terms of TOC and phosphorus removal as well. Increase of trans-membrane pressure difference was subtle, which might be attributed to the alternative creation of aerobic/anoxic conditions.
  • Nobuhiro Yamato, Katsuki Kimura, Taro Miyoshi, Yoshimasa Watanabe
    JOURNAL OF MEMBRANE SCIENCE 280 1-2 911 - 919 2006年09月 [査読有り][通常論文]
     
    There is a need for efficient control of membrane fouling in membrane bioreactors (MBRs), but there is still an insufficient understanding of the phenomena of membrane fouling and little is known about the influence of polymeric membrane materials on membrane fouling in MBRs. In this study, the influence of polymeric membrane materials on membrane fouling in MBRs was investigated on the basis of results of a pilot-scale experiment using real municipal wastewater. Two different polymers, polyethylene (PE) and polyvinylidene fluoride (PVDF), were examined side by side and the degree of fouling in each membrane was monitored. Also, analysis of the foulants in both membranes was carried out. The results obtained in this study demonstrated that PVDF is superior to PE in terms of prevention of irreversible fouling in MBRs used for treatment of municipal wastewater. Dissolved matter was mainly responsible for the irreversible fouling. Reversible fouling in the PVDF membrane might be related to an increase in sub-micron-sized organic matter that was mainly composed of carbohydrate. Composition of the foulants causing irreversible fouling differed considerably depending on the membrane polymeric materials. The results suggested that some fractions in organic matter in the mixed liquor have higher affinities with the membrane than do other fractions and consequently cause greater irreversible fouling. (c) 2006 Elsevier B.V. All rights reserved.
  • Y Watanabe, K Kimura, T Itonaga
    SEPARATION SCIENCE AND TECHNOLOGY 41 7 1371 - 1382 2006年 [査読有り][通常論文]
     
    This paper deals with the membrane fouling in membrane bioreactor (MBR). Based on the experimental data obtained in the MBR pilot plant study, the influence of F/M ratio on the irreversible and reversible fouling was discussed in the wide range of MLSS concentration. In the case of lower MLSS concentration (2,000-3,000 mg/L), irreversible fouling rate of membrane increased with increasing F/M ratio because of the accumulation of DOC in the mixed liquor. It seems that soluble microbial products with the similar size of the membrane pore will be most responsible for the irreversible fouling. In the case of higher MLSS concentration (8,000-12,000 mg/L), reversible fouling rate of membrane increased with increasing F/M ratio because of the increased suspension viscosity caused by the increased activated sludge size or volume even in the same MLSS concentration.
  • Katsuki Kimura, Hiroshi Yamamura, Yoshimasa Watanabe
    SEPARATION SCIENCE AND TECHNOLOGY 41 7 1331 - 1344 2006年 [査読有り][通常論文]
     
    For more efficient use of membrane technology in water treatment, it is essential to understand more about the fouling that requires chemical cleaning to be eliminated (i.e., irreversible fouling). In this study, five different MF/UF membranes and four types of organic matter collected from different origins were examined in terms of the degree of irreversible membrane fouling. Experimental results demonstrated that the extent of irreversible fouling differed significantly depending on the properties of both the membrane and organic matter. Among the tested membranes, UF membranes made of polyacrylonitrile (PAN) exhibited the best performance in terms of prevention of irreversible fouling. In contrast, MF membranes, especially one made of polyvinylidenefluoride (PVDF), suffered significant irreversible fouling. Conventional methods for characterization of organic matter such as specific ultraviolet absorption (SUVA), XAD fractionation, and excitation-emission matrix (EEM) were found to be inadequate for prediction of the degree of irreversible fouling. This is because these analytical methods represent an average property of bulk organic matter, while the fouling was actually caused by some specific fractions. It was revealed that hydrophilic fraction of the organic matter was responsible for the irreversible fouling regardless of the type of membranes or organic matter.
  • K Kimura, N Yamato, H Yamamura, Y Watanabe
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 39 16 6293 - 6299 2005年08月 [査読有り][通常論文]
     
    The main obstacle for wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling (i.e., deterioration of membrane permeability), which increases operating costs. For more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. However, there is a lack of information on membrane fouling in MBRs, especially information on features of components that are responsible for the fouling. We conducted a pilot-scale experiment using real municipal wastewater with three identical MBRs under different operating conditions. The results obtained in this study suggested that the food-microorganisms ratio (F/M) and membrane filtration flux were the important operating parameters that significantly influenced membrane fouling in MBRs. Neither concentrations of dissolved organic matter in the reactors nor viscosity of mixed liquor, which have been thought to have influences on fouling in MBRs, showed clear relationships with membrane fouling in this study. Organic substances that had caused the membrane fouling were desorbed from fouled membranes of the MBRs at the termination of the operation and were subjected to Fourier transform infrared (FTIR) and C-13 nuclear magnetic resonance (NMR) analyses. These analyses revealed that the nature of the membrane foulant changes depending on F/M. It was shown that high F/M would make the foulant more proteinaceous. Carbohydrates were dominant in membrane foulants in this study, while features of humic substances were not apparent.
  • K Kimura, H Hara, Y Watanabe
    DESALINATION 178 1-3 135 - 140 2005年07月 [査読有り][通常論文]
     
    Unintentional indirect potable water reuse, where wastewater effluent is used as a part of a downstream drinking water source, has become a great concern. In this case, a variety of organic micro-pollutants contained in wastewater effluent could create problems. Membrane bioreactors (MBRs) have gained significant popularity as an advanced wastewater treatment technology and might be effective in removing such organic micro-pollutants. Available information on the performance of MBRs regarding removal of micro-pollutants, however, is currently limited. This study examined the ability of submerged MBRs to remove pharmaceutically active compounds (PhACs). Experiments were conducted at an existing municipal wastewater treatment facility, and the performance of the MBRs was compared with that of the conventional activated sludge (CAS) process. Six acidic PhACs (clofibric acid, diclofenac, ibuprofen, ketoprofen, mefenamic acid, naproxen) and one acidic herbicide (dichloprop) were investigated. Compared with CAS, MBRs exhibited much better removal regarding ketoprofen and naproxen. With respect to the other compounds, comparable removal was observed between the two types of treatment. Removal efficiencies of the PhACs were found to be dependent on their molecular structure such as number of aromatic rings or inclusion of chlorine.
  • K Kimura, Y Hane, Y Watanabe
    WATER SCIENCE AND TECHNOLOGY 51 6-7 93 - 100 2005年 [査読有り][通常論文]
     
    Membrane fouling can be divided into two types: reversible fouling and irreversible fouling. The former can be easily canceled by physical cleaning (e.g., backwashing) while the latter needs chemical cleaning to be mitigated. For more efficient use of membranes, the control of irreversible membrane fouling is of importance. In this study, the effectiveness of pre-coagulation/sedimentation on irreversible membrane fouling was investigated, based on the pilot-scale operation of the membrane unit installed at an existing water purification plant. The membrane employed was a low-pressure ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cut-off of 750,000 daltons. Although pre-coagulation/ sedimentation significantly mitigated membrane fouling mainly through the reduction of reversible membrane fouling, the degree of irreversible fouling was not reduced by the pre-treatment. This was because the irreversible fouling observed during this study was mainly attributed to polysaccharides/protein like fractions of organic substances that cannot be efficiently removed by coagulation/sedimentation. Aluminium used as coagulant was thought to cause irreversible fouling to some extent but did not in the pilot operation, which could probable be explained by the fact that coagulation was conducted at relatively high pH (7.0) in this study.
  • K Kimura, Y Watanabe
    WATER SCIENCE AND TECHNOLOGY 52 10-11 427 - 434 2005年 [査読有り][通常論文]
     
    In this study, a novel membrane bioreactor (MBR) in which nitrification and denitrification simultaneously proceed in a single reaction chamber is proposed for advanced municipal wastewater treatment. Anoxic/aerobic environments are alternatively created in the proposed MBR by inserting baffles 14 inside the membrane chamber. The performance of the proposed baffled membrane bioreactor (BMBR) was examined at an existing municipal wastewater treatment facility based on long-term operation. Although the procedure was simple, insertion of the baffles actually created the alternative anoxic/aerobic environments in the chamber at a constant interval and showed a great improvement in the nutrient removal. The insertion did not cause any adverse effect on membrane permeability. In this study, almost complete elimination of NH4+-N was observed while around 8 mg/L of NO(3)(-)center dot N was detected in the treated water. The modification proposed in this study can immediately be applied to most existing MBRs and is highly recommended for more efficient wastewater treatment.
  • K Kimura, S Toshima, G Amy, Y Watanabe
    JOURNAL OF MEMBRANE SCIENCE 245 1-2 71 - 78 2004年12月 [査読有り][通常論文]
     
    As high quality drinking water becomes scarcer, unintentional indirect potable water reuse, where wastewater effluent is used as a part of a downstream drinking water source, has become a great concern throughout the world. In this case, a variety of organic micro-pollutants contained in wastewater effluent Could create problems. High pressure-driven membranes such as nanofiltration (NF) or reverse osmosis (RO) might be a powerful option to deal with such micro-pollutants, however, a lack of information on their performance is apparent. This study examined the ability of RO membranes to retain neutral (uncharged) endocrine disrupting compounds (EDCs) and pharmaceutically active compounds (PhACs). A total of 11 compounds were chosen so that a certain range of molecular weights and octanol-water distribution coefficients (K-ow) could be studied. With respect to membranes, two different materials (polyamide and cellulose acetate) were examined. Generally, the polyamide membrane exhibited a better performance in terms of the rejection of the selected compounds but the retention was not complete (57-91%). It was found that salt rejection or molecular weight cut-off (MWCO) that are often used to characterize membrane rejection properties did not provide quantitative information in terms of EDCs/PhACs rejection by NF/RO membranes. Molecular weight of the tested compounds could generally indicate the tendency of rejection for the polyamide membranes (size exclusion dominated the retention by the polyamide membrane) while polarity was better able to describe the retention trend of the tested compounds by the cellulose acetate membrane. The results obtained in this study imply that each membrane polymer material for NF/RO membranes, including ones that will be newly developed in the future, Would exhibit different trends in terms of rejection of organic micro-pollutants, which is determined by physico-chemical properties of the compounds. (C) 2004 Elsevier B.V All rights reserved.
  • 山村寛, 木村克輝, 渡辺義公
    環境工学研究論文集 41 257 - 267 Japan Society of Civil Engineers 2004年11月25日 [査読無し][通常論文]
     
    Membrane filtration has been gaining popularity in the various field. However, membrane fouling is an obstacle for wider application of this technology. Especially, the control of irreversible membrane fouling, which can be defined as fouling requiring chemical reagents to be mitigated, is of importance. The aims of this study were (i) to investigate the degree of irreversible fouling caused by different organic matters and (ii) to characterize the faulants that caused irreversible fouling. In this study, four different organic matters (commercially available humic acid, organic matters isolated from two drinking water sources and a wastewater treatment effluent) and membranes (two microfiltration (ME) membranes and two ultrafiltration (UF) membranes) were used. It was observed that the permeate flux did not decline in the UF membranes while there was a large flux decline in the MF membranes. Especially, a rapid flux decline was observed with the polyvinylidene fluoride (PVDF) membrane. The extents of fouling in the MF membranes were strongly depended on both the types of organic matters and membrane materials. A series of chemical analyses such as fluorescence excitation-emission matrix (EEM), specific UV adsorbance (SUVA) and ion chromatography (IC) were applied to elucidate which fractions of organic matter caused the irreversible fouling. SUVA of faulants was significantly lower than was determined for the feed water. This implies that the faulants had hydrophilic features. The results with EEM and IC also confirmed that a variety of hydrophilic compounds such as polysaccharide or protein-like compounds contributed to the formation of the irreversible fouling observed in this study.
  • K Kimura, Y Hane, Y Watanabe, G Amy, N Ohkuma
    WATER RESEARCH 38 14-15 3431 - 3441 2004年08月 [査読有り][通常論文]
     
    For more efficient use of membranes, the control of irreversible membrane fouling, which can be defined as fouling requiring chemical reagents to be mitigated, is of importance. In this study, irreversible fouling caused by constituents in surface water was investigated, based on a long-term pilot scale study. The membrane employed was a low-pressure hydrophobic ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cutoff of 750,000 Da. Various chemical reagents were examined to overcome the irreversible fouling that had developed through 5 months of continuous filtration. Among the tested cleaning reagents, alkaline (NaOH) and oxidizing reagent (NaClO) showed good performance in the restoration of membrane permeability, which implied that organic matter played an important role in the development of the irreversible fouling in this study. Chemical analysis, adsorptive fractionation methods, fluorescence excitation-emission matrix (EEM) and Fourie-transformed infra-red (FTIR) spectra analysis were applied to elucidate which fraction of organic matter caused the irreversible fouling. All of the analysis indicated that polysaccharide-like organic matter was responsible for the evolution of the irreversible fouling. In addition to organic matter, presumably iron and manganese also contributed to the irreversible fouling to some extent. (C) 2004 Elsevier Ltd. All rights reserved.
  • T Itonaga, K Kimura, Y Watanabe
    WATER SCIENCE AND TECHNOLOGY 50 12 301 - 309 2004年 [査読有り][通常論文]
     
    In this study, pilot scale experiments were carried out to examine membrane fouling occurring in membrane bioreactors (MBR) with or without pre-treatment (coagulation/sedimentation). Especially, the influence of suspension viscosity and dissolved organic matter (DOM) on membrane fouling was investigated. The pre-coagulation/sedimentation process improved the performance of a MBR in terms of membrane permeability by controlling irreversible fouling and formation of thick cake layer. The upper limit of MLSS concentration for an efficient operation in MBR without pre-treatment was suggested to be around 10 g/L based on the measurement of suspension viscosity. In-this study, it was difficult to directly relate membrane fouling to DOM detected in the membrane chamber. A series of laboratory scale dead-end filtration experiments was carried out to investigate which fractions in biomass suspension would be the most influential in the deterioration of membrane permeability. Based on the dead-end tests, it was shown that the deterioration of membrane permeability was mainly caused by the colloidal particle fraction in the biomass suspension.
  • K Kimura, G Amy, JE Drewes, T Heberer, TU Kim, Y Watanabe
    JOURNAL OF MEMBRANE SCIENCE 227 1-2 113 - 121 2003年12月 [査読有り][通常論文]
     
    The growing demand on water resources has increased interest in wastewater reclamation for potable reuse, in which rejection of organic micropollutants such as disinfection by-products (DBPs), endocrine disrupting compounds (EDCs), and pharmaceutically active compounds (PhACs) is of great concern. The objective of this study was to investigate the rejection of DBPs, EDCs, and PhACs by nanofiltration (NF) and reverse osmosis (RO) membranes as a function of their physico-chemical properties and initial feed water concentration. Experimental results indicated that negatively charged compounds could be rejected very effectively (i.e., >90%) regardless of other physico-chemical properties of the tested compounds due to electrostatic exclusion. No time-dependency was observed for rejection of charged compounds. In contrast, rejection of non-charged compounds was generally lower (<90% except for one case) and influenced mainly by the molecular size of the compounds. A clear time-dependency was observed for rejection of non-charged compounds, attributable to compound adsorption on the membrane. It was demonstrated that feed water concentration influenced rejection efficiency of the membrane. Experiments conducted at a low ng/l concentration range resulted in lower rejection efficiency as compared to experiments conducted at a mug/l range, suggesting the need to conduct experiments at the relevant concentration of interest. (C) 2003 Elsevier B.V. All rights reserved.
  • K Kimura, G Amy, J Drewes, Y Watanabe
    JOURNAL OF MEMBRANE SCIENCE 221 1-2 89 - 101 2003年08月 [査読有り][通常論文]
     
    This study addresses the adsorption of hydrophobic compounds at low concentration (similar to100 ppb) onto NF/RO membranes. In this study, three surrogate compounds and three NF/RO membranes were tested under cross-flow conditions. Experimental results showed that the adsorption of hydrophobic compounds was significant for neutral compounds and ionizable compounds when electrostatically neutral. Also, operating conditions such as the permeate flow rate (flux) had a significant effect on the degree of compound adsorption. A comparison of the adsorption observed in dynamic filtration tests with that in static batch adsorption tests suggests that more adsorption sites are accessible for molecules during membrane filtration due to the pressurized advective flow. It was observed that the concentration of the tested compounds changed during filtration tests due to adsorption. Therefore, an accurate evaluation of a given membrane in terms of the rejection of a hydrophobic compound is not possible until saturation of the membrane with the compound of interest is accomplished. The experimental results demonstrated that a relatively large amount of the feed water needed to be filtered to reach saturation conditions. (C) 2003 Elsevier B.V. All rights reserved.
  • K Kimura, M Nakamura, Y Watanabe
    WATER RESEARCH 36 7 1758 - 1766 2002年04月 [査読有り][通常論文]
     
    In this paper, a new method for removal of nitrate from groundwater, in which elemental sulfur-based denitrification (autotrophic denitrification) and membrane separation are combined, is proposed. By using a membrane, autotrophic denitrifiers, whose growth rate is considerably low, can be kept at a high concentration. The performance of the proposed process was examined through a long-term experiment in the laboratory using synthetic feed water. A rotating membrane disk module equipped with UF membrane (750.000Da) was used in this study. Complete removal of nitrate (25mg N/L) was achieved under the conditions of a biomass concentration of about 1000 mg protein/L and HRT of 160min. Dissolved oxygen concentration and sulfur/biomass ratio in the membrane chamber were found to be the key factors in maintenance of high-process performance, Deterioration in membrane permeability was insignificant. It was found that membrane filtration could be continued with a water flux of 0.5 m(3)/m(2)/day for about 100 days without any chemical membrane cleaning. The proposed process, however, caused a slight increase in assimilable organic carbon. Sulfide was not detected in the denitrified water. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • 膜濾過と生物膜を組み合わせた高度浄水処理プロセスに関する研究
    水道協会雑誌 81(4), 10 2002年 [査読有り][通常論文]
  • K Kimura, Y Watanabe
    2ND WORLD WATER CONGRESS: DRINKING WATER TREATMENT 2 2 177 - 183 2002年 [査読有り][通常論文]
     
    We have developed a novel biofilm-membrane reactor (BMR) in which a nitrifying biofilm is fixed on the surface of a rotating membrane disk. With this reactor, both strict solid-liquid separation and oxidation of ammonia nitrogen can be simultaneously performed. Based on the results obtained in previous bench-scale experiments, a pilot-scale study was conducted using river water at a water purification plant. The results obtained in the pilot study can be summarized as follows. (1) By implementation of pre-treatment (coagulation and sedimentation) and simple membrane cleaning (sponge cleaning), the filter run could be continued for 17 months without any chemical washing. (2) Sufficient nitrification was observed when water temperature was high. Deterioration in nitrification efficiency during winter was reduced by the addition of phosphorus. (3) In addition to nitrification, biological oxidation of AOC and manganese can be expected with the BMR. In this study, both AOC and manganese concentration in the permeate decreased to a level less than 10 mug/L. (4) Irreversible membrane fouling, which was thought to be mainly caused by manganese, became significant as the operation period became longer.
  • K Kimura, Y Watanabe, N Ohkuma
    MEMBRANES IN DRINKING AND INDUSTRIAL WATER PRODUCTION II 1 5-6 157 - 168 2001年 [査読有り][通常論文]
     
    The authors have proposed a novel biofilm-membrane reactor (BMR) in which nitrifying biofilm is fixed on the surface of the rotating membrane disk. With this reactor, both strict solid-liquid separation and oxidation of ammonia nitrogen can be simultaneously performed. Based on the knowledge obtained in the previous experiments with the bench-scale equipment, a pilot scale study was conducted using river water at a water purification plant. The results obtained in the pilot study can be summarized as follows: (1) A pilot scale BMR worked successfully even with the water from an actual drinking water source. By implementation of pre-treatment (coagulation and sedimentation), the filter run could be continued for more than 8 months without any chemical washing. (2) The sponge cleaning developed in this study was found to be very effective. This indicates that the accumulated cake resistance is dominant in the practical situation. (3) Sufficient nitrification was observed when water temperature was high. (4) In addition to the nitrification, biological oxidation of AOC and manganese can be expected with the BMR. In this study, both AOC and manganese concentration in the permeate decreased to a level less than 10 mug/L.
  • K Kimura, Y Watanabe, S Okabe, H Satoh
    WATER SCIENCE & TECHNOLOGY: WATER SUPPLY, VOL 1, NO 4 1(4), 111 4 111 - 118 2001年 [査読有り][通常論文]
     
    The authors have proposed a novel water treatment process in which nitrifying bacteria are fixed on the surface of rotating membrane disks. This biofilm-membrane process can perform strict solid-liquid separation and oxidation of ammonia nitrogen simultaneously. In this research, applicability of the conventional biofilm model (assuming the biofilm structure to be flat, homogeneous and continuous) to analysis of the biofilm developing in the proposed process was examined. A long-term operation for culturing the active nitrifying biofilm was carried out prior to kinetic investigation. By cryosectioning of the biofilm and image analysis, the thickness of the biofilm was determined to be 87 pm. From this biofilm thickness and the result of the batch ammonia consumption test, the intrinsic zero-order ammonia consumption rate of the biofilm was estimated precisely to be 930 g/m(3)/h. Using these parameters, the ammonia concentration profile in the biofilm was calculated by the conventional model, and the applicability of the model was examined by comparing the calculated profile with the ones measured with a microelectrode. The calculated profile was very close to the measured ones, which indicated feasibility of the conventional model to the analysis of the biofilm grown in the proposed process. The studied biofilm actually had a simple, i.e. flat, homogeneous and continuous, structure due to membrane filtration. This was the reason why the conventional model could still be employed. In the analysis of the data dealing with low concentrations of ammonia, however, first-order kinetics should be used. The first-order ammonia consumption rate constant of the studied biofilm was estimated to be 808 h(-1).
  • K Kimura, Y Watanabe, N Ohkuma
    WATER RESEARCH 34 11 2895 - 2904 2000年08月 [査読有り][通常論文]
     
    The authors have proposed a novel membrane process where nitrifying bacteria are fixed on the surface of the rotating membrane disks. With this proposed membrane process, the simultaneous performance of the strict solid liquid separation and the oxidation of ammonia is enabled. In this study, three long-term experiments were carried out and the distribution of the filtration resistance and the efficient cleaning method of the proposed membrane process were investigated. The membrane Aux was fixed at 0.8 m(3)/m(2)/d and the feed ammonia concentration was controlled within the range of 0.1-1.0 mg-N/l. in the proposed membrane process, the filtration resistance caused by the accumulated cake was dominant. The shear-stress induced by the increased disk's rotational speed was found to be efficient for removing the accumulated cake, However, this cleaning method did not work well when feed water contained suspended particles at 10 of turbidity unit. In order to increase the cleaning efficiency, a small quantity of sponge particles were introduced into the membrane chamber and the disk's rotational speed was increased. This membrane cleaning method using sponge particles proved so effective that the filtration resistance due to the accumulated cake was completely cancelled. Membrane filtration could be continued for more than 3000 h due to the implementation of this cleaning method utilizing sponge particles once every 1000-1500 h. For the maintenance of the ammonia oxidation rate, however, a part of the detached nitrifiers had to be returned to the membrane chamber after the membrane cleaning. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • Y Watanabe, K Kimura, T Suzuki
    WATER SCIENCE AND TECHNOLOGY 41 10-11 9 - 16 2000年 [査読有り][通常論文]
     
    This paper deals with two recent developments made by the authors about the hybrid membrane systems applicable to the water purification. The performance of a hybrid MF membrane system with circulating powdered activated carbon and condensed sludge has been studied using a pilot plant. The powdered activated carbon was intermittently dosed to the system for adsorbing mainly the humic substances. Manganese ions and ammonia nitrogen were biologically oxidized by the iron-oxidizing bacteria and ammonia oxidizing bacteria inhibiting the condensed sludge. In the hybrid MF membrane system, decreasing rate of the permeability was much less than that of a conventional MF membrane process. This may result from the reduced organic loading to the membrane due to the adsorption of humic substances onto the powdered activated carbons. A novel UF membrane process was also developed, where the nitrifying bacteria are fixed on the surface of the rotating disk membranes. With this membrane process. the simultaneous performance of the strict solid-liquid separation and the biological ammonia oxidation are possible. In order to increase the washing efficiency, a small quantity of the sponge particles were introduced into the membrane chamber and then the disk rotational speed was increased. This membrane washing method using sponge particles was so effective that the filtration resistance due to the accumulated cake was completely cancelled.
  • 木村克輝
    環境工学研究論文集 36 287 - 294 公益社団法人 土木学会 1999年 [査読無し][通常論文]
     
    The authors have proposed a novel membrane process for drinking water treatment in which nitrifiers are fixed on the membrane surface. With this proposed membrane process, strict solid-liquid separation by membrane filtration and oxidation of ammonia can be performed simultaneously. Fixed nitrifiers are supposed to cause membrane filtration resistance to some extent. The magnitude of the filtration resistance caused by the fixed nitrifiers for oxidizing low concentrations of ammonia was evaluated in this study. Experimental results showed that the fixation of the nitrifiers on the membrane surface had a little influence on the increase of the filtration resistance. Most of the resistance was caused by trace inorganic and organic substances contained in the feed water (tap water). The filtration resistance was divided into the cake resistance and the irreversible fouling resistance. The nitrifiers for the oxidation of low concentrations of ammonia seemed to increase the cake resistance a little and hardly cause the irreversible fouling.
  • 木村 克輝, 渡辺 義公, 大熊 那夫紀
    土木学会論文集(]G0007[) 608 608 87 - 95 公益社団法人 土木学会 1998年 [査読有り][通常論文]
     
    本研究では, 回転平膜の表面に硝化細菌を保持しながら膜ろ過を行う膜処理プロセスを用いて, 低濃度アンモニア性窒素 (NH4+-N) の酸化を行った場合に形成される膜ろ過抵抗について検討した. 実験結果より, 本プロセスにおける膜ろ過抵抗は運転開始時に膜面に付着させる微生物群の特性に強く依存することが明らかとなった. 膜ろ過抵抗の分布について検討した結果, 本プロセスでは全膜ろ過抵抗の70-80%が膜面に付着・蓄積したケーキに起因するものであった. 約500時間に一度の頻度で付着ケーキの除去, 排出を行いながら長期連続運転を試みた結果, 約3000時間の運転継続が薬品洗浄無しで可能であった. 付着ケーキに起因する抵抗以外の膜ろ過抵抗は, 有機物質が膜細孔を覆い隠すことで発生していた.
  • K Kimura, Y Watanabe, N Ohkuma
    WATER SCIENCE AND TECHNOLOGY 38 4-5 443 - 452 1998年 [査読有り][通常論文]
     
    Membrane filtration and oxidation of ammonia were simultaneously performed by using a rotating membrane disk module. Nitrification performance, composition of the accumulated cakes on the membrana and the filtration resistances were investigated under five different operating conditions. The filtration resistance due to the accumulated cake on the membrane was found to be dominant in this treatment method, compared to the resistance due to the micropore plugging or irreversible adherence. The cake consisted mainly of iron, humic substances and bacteria. The possibility that extracellular polymeric substances were related to the cake resistance was also shown. The composition of the cake depended on the length and the condition of operation. Accumulation of ammonia oxidizers caused by oxidation of low concentrations of ammonia (less than 1 mg/l) did not increase transmembrane pressure significantly. Therefore, the application of this treatment method for drinking water treatment is feasible. Filtration resistance due to the micropore plugging or irreversible adherence to the membrane was caused by organic substances. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • Y Watanabe, K Kimura, S Okabe, G Ozawa, N Ohkuma
    WATER SCIENCE AND TECHNOLOGY 36 1 51 - 60 1997年 [査読有り][通常論文]
     
    For the oxidation of low concentrations of NH4+-N, conventional biofilm reactors such as a rotating biological contactor encounter difficulty due to mass transport limitation of NH4+-N. Therefore, the authors have developed a novel biofilm-membrane reactor, in which biomass is fixed on the surface of rotating membrane disks to enhance NH4+-N transport into the biofilm. Three long-term bench-scale experiments were carried out and sufficient nitrification efficiency was obtained even at low levels of NH4+-N. The experimental results were evaluated in comparison with model simulation. (C) 1997 IAWQ. Published by Elsevier Science Ltd.
  • 木村 克輝, 渡辺 義公, 大熊 那夫紀
    土木学会論文集(]G0007[) 552 552 43 - 52 土木学会 1996年 [査読有り][通常論文]
     
    本研究では, 分離膜表面に生物膜を付着させて低濃度アンモニア性窒素の硝化を行った. その結果, 従来の生物膜処理に比べて効率的な処理が行われることを確認した. その理由は生物膜への物質移動を膜ろ過に伴う移流によって増加させたこと, 拡散層の厚さを減少させたこと, 処理水を生物膜基底部から得たことによる. 微生物活動に伴う代謝産物が主な膜閉塞の原因と考えられるが, 保持生物量の適正化によって1000時間程度の膜ろ過継続が可能であった.

その他活動・業績

特許

受賞

  • 2018年 国際水協会 IWAフェロー
     
    受賞者: 木村 克輝
  • 2017年 最優秀論文賞、Frontiers International Conference on Wastewater Treatment, Palermo.
     
    受賞者: 木村 克輝
  • 2011年 日本水環境学会論文賞
     
    受賞者: 木村 克輝
  • 2010年 クリタ水・環境科学研究優秀賞
     
    受賞者: 木村 克輝
  • 2004年 土木学会年次学術講演会優秀講演者
     
    受賞者: 木村 克輝
  • 2003年 土木学会年次学術講演会優秀講演者
     
    受賞者: 木村 克輝
  • 2001年 水環境学会論文奨励賞(廣瀬賞)
  • 2001年 土木学会年次学術講演会優秀講演者

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年04月 -2025年03月 
    代表者 : 三好 太郎, 木村 克輝
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2021年04月 -2025年03月 
    代表者 : 木村 克輝, 西村 紳一郎, 羽深 昭
     
    ベンチスケールのMBR実験システムを構築し、実下水処理場に実験装置を設置して連続ろ過実験を繰り返し実施した。本研究で提案・確立を行うエネルギー回収型MBRでは深刻な膜ファウリングの発生が確実に起こるため、これに対処するための担体を用いた機械的洗浄と薬品併用逆洗（CEB）を実施しながら連続ろ過運転を行った。HRT、SRT、DOを様々に変化させて実験を行い、有機物回収率、膜ファウリング発生度、処理水水質のそれぞれが高いレベルで調和するような運転条件の探索を試みた。HRTを極短の1.5-2時間、SRTも極短の0.5日とすることで、有機物回収率（初沈流入水に対して）は70％を超過する結果が得られた。実下水を用いた実験であったことからDOを一定範囲に制御することが難しく、MBR内のDO濃度は大きく変動した（1-7 mg/L）。処理水中のCOD濃度は20 mg/L程度となり、高い有機物回収率と処理水中の有機物濃度低減を同時に達成可能であることを実証した。膜ファウリングの発生については、CEBに用いる次亜塩素酸の濃度が洗浄効果に大きな影響を及ぼすことを観察した。本年度の研究では50-1000 ppmの範囲でCEBに用いる次亜塩素酸の濃度を変化させたが、最も安定したMBRの運転が可能になったのは次亜塩素酸の濃度を50 ppmに設定した時であった。過度に高い薬品濃度は微生物からの有機物放出を誘引し、MBR内の汚泥ろ過性を低下させるものと考えられた。CEBに用いる次亜塩素酸濃度を50 ppm とし、正味の膜透過水フラックスを20 LMHに設定した実験では５日間程度はほとんど膜ファウリングが発生しない状況を繰り返し観察した。
  • 日本学術振興会：科学研究費助成事業 挑戦的研究(開拓)
    研究期間 : 2018年06月 -2021年03月 
    代表者 : 木村 克輝, 渡部 靖憲
     
    都市下水の中に含まれる有機物を嫌気性消化すればエネルギーを回収できるが、下水中の有機物濃度が低すぎるために嫌気性消化の都市下水への直接適用は難しい。一方、都市下水中有機物の大半がコロイド寸法以上のサイズで存在している。下水を膜ろ過処理することで有機物を回収・濃縮できるはずであるが、深刻な膜の目詰まり（ファウリング）が問題となる。本研究は、従来の研究では検討されなかったような高強度の膜洗浄を実施して、下水の直接膜ろ過を長期にわたり継続することに挑戦するものである。高強度の膜洗浄実施を可能にするために、物理的・化学的耐性が高いセラミック膜を用いて実験を行った。有機膜の場合には膜破損が生じる粒状担体の流動に伴う膜面洗浄、高濃度の薬品を用いた高頻度の薬品併用逆洗（CEB)を実施することにより、下水の50倍濃縮を試みた。実都市下水処理場にベンチスケール膜ろ過装置を設置して、最初沈殿池流出水を原水とした連続ろ過実験を行った。膜ろ過は2段階で行い、第1段目で2倍、第2段目で25倍濃縮して、トータルで50倍濃縮を達成した。粒状担体の充填率、膜透過水フラックスの設定値、CEBに用いる薬品の濃度、CEBの実施頻度を検討項目とし、連続実験を行った。充填率については膜分離槽容積の30％相当、膜透過水フラックスは一段目タンク6.5LMH、二段目タンク4.2LMH、CEBについては1250ppmクエン酸を用いて6時間に一度の頻度で実施することにより、一ヶ月程度の連続運転が可能であることを確認した。この実験で観察された膜ファウリングは大半が膜表面に蓄積したケーキ層によるものであり、物理的洗浄の効率を高めることで、より高いフラックスで安定した運転を長期にわたって実施することが可能であることが示唆された。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 木村 克輝, 西村 紳一郎, 山村 寛
     
    表流水中有機物の中で僅かな割合を占める高分子量親水性有機物（バイオポリマー）が、表流水の膜ろ過処理において主な膜ファウリング発生成分であることが明らかになっている。関連する研究のほとんどで、バイオポリマーは分子量1万ダルトン以上の分子量を有する成分として一括して扱われているが、バイオポリマーは様々な成分の混合物であることが確実視される。本研究では一括して扱われてきたバイオポリマーを細分化して、膜ファウリング発生において真に重要となるバイオポリマー成分を特定することを目指している。本年度はLC-OCDの改良により可能となったバイオポリマーのサイズに基づく細分化を適用し、巨大バイオポリマー（分子量100万ダルトン以上）がMF膜のファウリングを発生させる一方で、UF膜のファウリングについては分子量100万ダルトン未満のバイオポリマーが主な原因となっていることを究明した。バイオポリマーの濃縮・精製を大容量で行うための方法開発も行い、精製バイオポリマーの回収率と純度を上げるために精製過程におけるイオンバランスの調整が必要であることを見出した。精製バイオポリマーを異なる細孔径を有するMF/UF膜で疑似クロスフローろ過し、これまで一括して得られるのみであったバイオポリマーを４つのサイズ画分に分離して得ることに成功した。これら４つのサイズ画分の膜ファウリング発生ポテンシャルをPVDF膜を用いたろ過実験またはQCM-Dにより評価することが可能になっている。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 渡辺 義公, 木村 克輝, 羽深 昭, 山村 寛
     
    都市下水をMBRで処理し、処理水と残存する窒素とリンを活用して微細藻類を培養しそれを魚介類養殖のためのタンパク質・油脂飼料生産システムに導入することを目的とした。研究成果は、1)MBR：渡辺が特許を所有する単槽式仕切り板挿入型MBR(bMBR)の実験により仕切り板内のORPとサイクル時間を調整すれば、処理水の全窒素濃度を微細藻類の培養に最適な値に調整できた。膜の長尺化と高充填密度化によって、運転動力を0.2 kwh/m3まで低下できた、2)微細藻類：MBR処理水により培養した微細藻類はタンパク質含有量がカタクチイワシと同等であり、有害金属濃度も飼料基準値以下であった。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 木村 克輝, 西村 紳一郎, 山村 寛
     
    本研究では、生体内試料から糖鎖のみを選択的に回収するグライコブロッティングに着目し、膜処理において膜を閉塞させるバイオポリマーを効率的に除去できる前処理方法の確立を試みた。常温下ではグライコブロッティングによるバイオポリマーの除去は限定的であったが、アニリンなどの触媒あるいは酸化剤の併用により常温下でもバイオポリマーの除去が可能となった。バイオポリマーにはグライコブロッティングにより除去しやすいものとしにくいものが混在していることが分かり、バイオポリマーの細分類が必要となった。バイオポリマーの分析法として国際標準となっている方法を改良し、バイオポリマーを細分類して分析することに成功した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 佐野 大輔, 大村 達夫, 中込 治, 木村 克輝, 加藤 毅
     
    本研究では、胃腸炎ウイルスの糖鎖認識を活用した下水処理過程における胃腸炎ウイルス制御方法を確立することを目的とした。平成２６年度には、糖鎖マイクロアレイを用いてノロウイルス粒子が認識可能な糖鎖を検索した。平成２７年度には、ノロウイルス粒子の糖鎖認識プロファイルをもとにGD1a陽性細菌を単離した他、HBGA陽性細菌を用いてノロウイルスの精密膜ろ過実験を行った。平成２８年度には、下水処理過程におけるHBGA陽性細菌の動態を調査するためにHBGA合成遺伝子の同定を行った他、HBGAを認識するロタウイルスHAL1166株を用い、HBGA陽性細菌との共存状態での膜ろ過によるウイルス除去性能を評価した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2013年10月 -2016年03月 
    代表者 : 渡辺 義公, 木村 克輝, 山村 寛, 佐藤 久, 羽深 昭
     
    膜分離活性汚泥法(MBR)の改良型として渡辺が考案したbuffled MBRは単一槽で有機物酸化、窒素除去、リン除去が行える画期的方式である。本研究ではbuffled MBRの「信頼性の向上＋低コスト化」及びそこでの「余剰汚泥からのリン回収システム」について研究した。処理能力15 m3/日のパイロットプラント実験によって以下の点を明らかにした。長さ3mのPTFE中空糸膜による実験から動力消費量として0.35kWh/m3を得た。嫌気性MBRにジルコニアメソ構造体を担持したMF膜を用いることで画期的な余剰汚泥からのリン回収システムか構築できる可能性を示した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 木村 克輝, 比能 洋, 相沢 智康
     
    多糖中に含まれるアルデヒド基とアミノオキシ基間の特異的結合を利用したグライコブロッティング法の適用により、高解像度のMALDI-TOF/MS分析を行うことでMBRにおける膜ファウリング多糖の構造と起源について検討した。本研究の結果、抽出ファウリング多糖と上澄み液中の多糖には共通する多糖構造が必ずしも多くないことが示された。MBRの膜ファウリング発生には、莢膜多糖（CPS）あるいはリポ多糖（LPS）が重要な関与をしている可能性が本研究により得られたMALDI-TOF/MSスペクトルの検討および質量数ピークの微生物多糖データベースとの照合により示された。
  • 日本学術振興会：科学研究費助成事業 基盤研究(S)
    研究期間 : 2009年05月 -2014年03月 
    代表者 : 船水 尚行, 高橋 正宏, 大瀧 雅寛, 礒田 博子, 牛島 健, 木村 克輝, 伊藤 竜生, グイザニ モクタール, 韓 畯奎, 柿本 貴志, 小野田 優, 木村 克輝
     
    「混ぜない」，「集めない」というコンセプトを適用した新しい資源回収型排水処理体系を提案し，３つのモデル(水・衛生問題解決と資源回収を同時に行う途上国農村モデル，途上国スラムモデル，自然共生型日本里山モデル)に必要な要素技術とその評価法を開発した．開発した主要な技術は①糞便をコンポス化するトイレ技術，②尿の濃縮技術，③尿中窒素とリンの回収技術，④回収資源の農業利用技術，⑤雑排水の再生利用技術，⑥バイオアッセイによる毒性評価技術，⑦病原微生物不活化評価技術である．窒素，リン，水フローの調査・解析により，ブルキナファソ農村とインドネシアのスラム街での新システムの導入可能性が示された．
  • 日本学術振興会：科学研究費助成事業 若手研究(A)
    研究期間 : 2009年 -2011年 
    代表者 : 木村 克輝
     
    本研究では、実都市下水を処理するMBRにおいて膜ファウリングに関与しているタンパク質の詳細な構造解析を試みた。閉塞膜より抽出した試料の前処理方法を検討し、二次元電気泳動によるファウリングタンパク質の分離に成功した。分子量と等電点に基づき分離したファウリングタンパク質のアミノ酸配列解析により、Pseudomonas属に属する細菌の外膜タンパク質がMBRにおける膜ファウリングに深く関与していることが示された。
  • 日本学術振興会：科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2008年 -2009年 
    代表者 : 木村 克輝, 定金 正洋
     
    水処理各方面で様々な種類の分離膜が導入され始めているが、未だに主流技術とはなりえていない。その主な原因は膜ファウリングに伴う運転コストの増加および溶解性低分子量成分の除去性である。本研究は、ナノスケールでの規則的かつ立体的な構造制御が可能となっているカーボンナノファイバーを分離膜表面に固定することで、従来は考えられなかった新機能を有する分離膜創生を行い、上述した問題の解決を目指すものである。21年度は、平膜状アルミナ多孔体上にカーボンナノファイバーを固定化する条件の最適化を検討し、以下の条件を確立した。平膜状アルミナ多孔体(WhatmanアルミナフィルターAnodisc 25)を0.3M硝酸ニッケルのエタノール溶液に浸し、超音波バス中で10分間超音波処理を行った。そめ後、硝酸ニッケル溶液から平板状アルミナ多孔体を取り出し、この硝酸ニッケル溶液の染み込んだ平板状アルミナ多孔体を300度に加熱している焼成炉に1時間入れ、アルミナ多孔体中の硝酸ニッケルを酸化ニッケルに変換した。その後、この酸化ニッケルを担持した平板状アルミナ多孔体をメタンガス流通下(毎分20ml)、550度で2時間反応させることにより、カーボンナノファイバーを生成させた。この方法により平板状アルミナ多孔体上全てにカーボンナノファイバーを生成させることが出来ることが確認できた
  • 日本学術振興会：科学研究費助成事業 若手研究(A)
    研究期間 : 2006年 -2008年 
    代表者 : 木村 克輝
     
    従来型の下水処理技術では除去が難しい医薬品類による水環境及び水道水源の汚染が顕在化している。本研究では、次世代の下水処理技術として注目されている膜処理を用いた場合の医薬品除去性について検討した。膜分離活性汚泥法やナノろ過、逆浸透処理による医薬品の除去性は従来型下水処理と比較して大幅に高くなる。生物処理部の操作条件はシステム全体における医薬品除去性に大きな影響を及ぼすことが明らかとなった。また、下水処理過程において医薬品は完全に分解されるわけではなく、構造が特定されない中間生成物として放流されるものがあることを示した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2003年 -2004年 
    代表者 : 岡部 聡, 木村 克輝
     
    本研究では糞便性指標微生物の遺伝子マーカーと化学マーカーを組み合わせた迅速(1-2日程度)かつ簡便な、糞便性汚染源の特定と汚染度の定量的評価手法の開発を行うことを目的とした。腸内蛋白質分解細菌の最優占種であるBacteroidesに着目し、培養を必要としない分子生物学手法(16S rDNAクローンライブラリー法やTerminal Restriction Fragment Length Polymorphism : T-RFLP法、定量PCR法)を用い、宿主特有のBacteroidesの16S rRNA遺伝子配列(遺伝子マーカー)を特定・探索することにより、水環境中の糞便汚染源(人間、牛、豚等)を特定する。研究成果は以下のように要約される。 宿主動物(人間、牛、豚)毎に特異的なBacteroides種が存在し、宿主動物を認識することが可能な16SrRNA遺伝子配列(遺伝子マーカー)を見つけ出すことに成功した。これによって、これら特異的なBacteroides属を指標微生物とすることにより、糞便汚染源の特定が可能であることを示唆している。次に、これら宿主特異的遺伝子マーカーを迅速かつ簡便に検出・定量するために、これらの遺伝子マーカーに特異的なPCRプラーマーのセットを7つ設計することができた。これら設計したPCRプラーマーセットを用いたT-RFLP法を確立した。この結果、宿主動物毎に特異的なDNA断片長を有するクローンが河川環境中に多く存在することが確認された。したがって、これらのDNA断片は宿主動物毎の遺伝子マーカーとなることが確認できた。また、遺伝子マーカーの迅速な定量を行うために、それぞれのプライマーセットに対応するReal-timePCR法の反応条件を確立した。T-RFLP法およびReal-timePCR法による解析は、DNA抽出から定量まで約8時間で終了し、かつ培養法によるバイアスを排除できるため、より正確に複合微生物系内に存在する各種糞便性大腸菌および病原細菌の特定・定量および汚染源の特定・モニタリングが可能となると思われる。また、検出限界は極めて低く、高感度かつ特異的な糞便性大腸菌汚染の指標となることが明らかとなった。
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2003年 -2004年 
    代表者 : 木村 克輝
     
    本年度は、膜分離活性汚泥法(Membrane bioreactor, MBR)による医薬品由来化合物(PhACs)除去性の検討を行った。MBRは膜を用いた次世代の下水処理技術として注目されている技術であるが、PhACsのMBRによる除去性に関する検討例は現時点でほとんど存在していない。実験は、実都市下水処理場に設置したパイロットスケールのMBRを用いて行った。標準活性汚泥法を採用している実都市下水処理場最終沈殿池流出水中のPhACs濃度とMBR処理水中のPhACs濃度を比較することにより、MBRのPhACs除去性について評価した。検討の対象としたPhACsのうち、clofibric acid、ibuprofen、ketoprofen、naproxen、fenoprofen、mefenamic acid、diclofenac、primidone、carbamazepineの9種類のPhACsが流入下水から検出された。今回検討の対象としたPhACsは、各処理プロセスにおける除去性によって3つのグループに分けることができた。ibuprofenはMBRと活性汚泥法の両方において良好に除去されていたが、diclofenacはどちらの処理法によっても顕著な除去は観察されなかった。また、ketoprofen、mefenamic acid、naproxen、fenoprofen、clofibric acidは活性汚泥法よりもMBRにおいて効果的に除去されていた。これらのPhACs除去性とPhACsの構造との関連性に着目すると、PhACsの構造に含まれるベンゼン環数が除去性に大きな影響を及ぼしているようであった。構造中のベンゼン環数が1つのibuprofenについては、MBRと活性汚泥法は同程度の除去性を示したが、ベンゼン環数が2つのketoprofen、mefenamic acid、naproxen、fenoprofenについては活性汚泥法よりもMBRにおいて良好な除去が達成された。ベンゼン環とハロゲン基をそれぞれ2つ有するdiclofenacはMBR/活性汚泥法の双方において顕著な除去は観察されなかった。PhACsの構造中にベンゼン環やハロゲン基が多く存在する物質ほど生物処理による除去が困難になるものと推測される。MBR/活性汚泥法間におけるPhACs除去性の差異は、両プロセスにおけるSRTの長短によるものであったと考えられる。MBRではSRTを極めて長く設定できるため、増殖速度の遅い微生物種が増殖できることに加え、元々存在していた微生物がPhACsに対して代謝活性を獲得する可能性がある。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2002年 -2004年 
    代表者 : 渡辺 義公, 岡部 聡, 木村 克輝
     
    1)膜ファウリング機構の解明および抑制 実都市下水を用いた多系列の膜分離活性汚泥処理実験を行い、運転条件、前処理の有無が反応槽内汚泥の性状に及ぼす影響について検討した。反応槽内汚泥濃度の上昇に伴って槽内汚泥の粘度が上昇し、膜ろ過運転を困難にするが、特に汚泥濃度が10,000mg/Lを超過する際に粘度の上昇が顕著になる傾向が観察された。前凝集沈殿処理を行うことでこれらの粘度上昇は良好に抑制されうることを見いだした。 2)ハイブリッドMBRでは窒素除去率が低いことを改善するために、PVDF製のMF平膜を用いたMBR内に仕切り板を入れて、MBRの水位を変化させて槽内に好気部と無酸素部を同時に形成する新たなMBRを開発した。このMBRでは処理水の全窒素濃度が5mg/l程度となった。また、MBR内の生物相の解析によって、MBR内には糸状細菌であるChloroflexiが活性汚泥ばっき槽内と比較して極めて高い存在割合を占めていることを明らかにした。Chloroflexiは死滅細菌由来の有機物のスカベンジャーとして機能し、溶解性有機物の蓄積による膜ファウリングの抑制に寄与していることが示唆された。 3)処理水の再利用の観点から、Bacteroides属とPrevotella属を指標として、迅速かつ正確に人獣の糞便由来の病原性微生物の存在をチェックできる新たな分子生物学的手法を開発し、実河川の水質測定に適用した。その結果開発された手法によって、人、牛、豚の糞便汚染を区別できることが明らかになり、処理水の安全性の確認のみではなく、河川の糞便汚染の汚染源を特定できるようになった。 4)新規吸着剤であるジルコニアメゾ構造体(ZS)をリン酸吸着に適用した結果、ZSに含まれるSO_4^<2->とOH^-がリン酸イオンと陰イオン交換することで、リン酸を選択的に吸着する機構を明らかにした。その最大吸着能約3500μM/gZSであり、既存の吸着剤の1.7倍に達した。ZSに吸着されたリン酸はクエン酸溶液(pH=4.5)やNaOH溶液に浸すことで容易に溶出した。今後はZSの再生方法と高濃度・高純度に濃縮されたリン酸溶液からの硝析脱リンによるリン回収技術の確立を計画している。
  • 水中溶存有機物の分画・評価
    科学研究費補助金
    研究期間 : 2000年 -2004年
  • 膜ファウリング機構に関する研究
    科学研究費補助金
    研究期間 : 2000年 -2004年
  • Characterization of dissolved natural organic matter
    Grant-in-Aid for Scientific Research
    研究期間 : 2000年 -2004年
  • A study on membrane fouling mechanism
    Grant-in-Aid for Scientific Research
    研究期間 : 2000年 -2004年
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2000年 -2001年 
    代表者 : 渡辺 義公, 木村 克輝
     
    千歳川表流水を原水として、凝集条件の異なるジャーテストとUF膜回分ろ過実験を行い、UF膜ろ過のろ過サイクルにおける膜ファウリングの発現および溶解性有機成分の除去性に及ぼす凝集沈殿処理の影響を検討した。噴流攪拌固液分離槽(JMS)による凝集沈殿を前処理としたUF膜連続ろ過実験を行い、長時間の運転において膜ファウリングの発現及び溶解性有機成分の除去性に及ぼす影響も評価した。その結果、凝集沈殿をUF膜ろ過の前処理として用いると、膜ファウリングが低減化され、溶解性有機成分の除去性が著しく向上することが確認された。また、UF膜ろ過の前処理としての凝集沈殿の効果は、pHや凝集剤注入率によって大きな差があることから、適切な凝集条件の選択が重要である。 長時間の定流量全量UF膜ろ過における、物理洗浄条件の違いが膜ファウリングの抑制に及ぼす影響について検討した。水逆洗とエアスクラビングを併用すると、水逆洗のみの場合に比べて、不可逆ケーキ層抵抗の上昇が極めて緩やかとなった。物理洗浄排水の分析より、膜で阻止された高分子フミン質、懸濁成分および金属成分が水逆洗とエアスクラビングの併用によって、良好に剥離できたためであることがわかった。洗浄時間及び洗浄強度の異なる物理洗浄の増加に伴い、不可逆ケーキ層抵抗の上昇は緩やかになったが、洗浄時間には最適値が存在した。 膜ファウリングの制御と処理水質の向上を目的に、MF膜ろ過の前処理としてオゾン酸化を行った。異なるオゾン注入率と膜ろ過前後の残留オゾンの、膜ろ過運転性と処理水質を検討した。前オゾン酸化によって、E260を指標とするフミン質の除去率はオゾン酸化無しの場合に比べて1.5〜2.0倍向上したが、TOC除去率は若干低くなった。前オゾン酸化後空気曝気してオゾンを残留させなかった場合は、全マンガン除去率は約90%であったが、膜面にオゾンを残留させた場合の全マンガン除去率は約50%であった。前オゾン酸化して膜ろ過すると、ろ過水のAOCは千歳川を直接膜ろ過した場合の2.5〜8.2倍となった。前オゾン酸化により膜ろ過運転性が向上した。特に、膜透過水にオゾンが残留していた場合に、より安定した膜ろ過運転が可能であった。前オゾン酸化による膜ろ過運転性の向上は、(1)オゾン酸化による有機成分の低分子化、(2)膜面に残留するオゾンによる膜で阻止された有機・無機成分に対する物理洗浄効果の向上、によると考えられる。回転平膜の表面に微小量の硝化細菌を主体とする生物膜を保持しながら膜ろ過を行う膜処理プロセスを開発した。本プロセスでは、膜ろ過と低濃度アンモニア性窒素、マンガンイオン、生物代謝性有機物(AOC)の酸化が同時に行われる。膜ろ過抵抗について検討した結果、本プロセスでは、全膜ろ過抵抗の70〜80%が膜面に付着・蓄積したケーキに起因した。本水処理装置では、膜の回転作用を利用したスポンジ片による膜洗浄法が有効であった。この洗浄法と本装置の処理性を確認するために、長期間に亘るパイロットプラント実験を行った。その結果、スポンジ洗浄のみで約1年間の運転が可能であった。処理水質についても、水温が15℃以上では、アンモニア性窒素濃度、全マンガン、AOCの濃度はそれぞれ0.01、0.005、0.001mg/l程度であった。
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    研究期間 : 2000年 -2001年 
    代表者 : 木村 克輝
     
    本年度は、有機物濃度の高い水道水源(江別市千歳川表流水)および有機物濃度の低い水道水源(札幌市豊平川表流水)を対象として、三次元励起・蛍光スペクトル(EEMs)、各種樹脂を用いるLeenheerの方法による溶存有機物のキャラクタリゼーションを行い、両者の関係を考察した。この結果、比較的短時間で得ることのできるEEMsから、Leenheerの方法による有機物の分画結果を予測しうることがわかった。並行して千歳川表流水、豊平川表流水それぞれを用いたパイロットスケール膜ろ過実験を実浄水場において行い、長期間にわたり実験を継続することによって膜を閉塞させた。これらの膜の一部分を採取し、膜を閉塞させた有機成分を酸・アルカリなどの各種薬品により抽出するとともに、抽出前後の膜透過性能の変化を小型膜ろ過モジュールによって評価した。薬品によって抽出された成分のEEMsを検討することによって、溶存有機物中のどのような画分が膜閉塞、特に不可逆的な膜閉塞に深く関与しているかを検討した。この結果、不可逆的な膜閉塞は主に疎水的酸性成分によって引き起こされていることが示唆された。強アルカリを用いて有機成分の抽出を行う際には、膜本体からの親水性成分の漏出が無視できない量となった、この部分の影響をどのように除去しうるかが課題として残されている。今後はより広範な範囲の水・膜の組み合わせについて本研究で開発した膜閉塞成分検討法を適用してゆくことで、原水水質に対応した合理的膜選択手法の確立に近づくことができるものと考えられる。
  • メンブレンバイオリアクターの最適化
    ＪＳＴ戦略的創造研究推進制度（研究チーム型） （戦略的基礎研究推進事業：ＣＲＥＳＴ）
    研究期間 : 1997年 -2001年
  • Optimization of membrane bioreactor
    JST Basic Research Programs (Core Research for Evolutional Science and Technology :CREST)
    研究期間 : 1997年 -2001年
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 1996年 -1998年 
    代表者 : 渡辺 義公, 木村 克輝, 岡部 聡, 但野 利秋, 中埜渡 丈嘉
     
    (1) 凝集・高速固液分離・生物酸化を組み合わせた高度下水処理システム 固液分離プロセスの更なる効率化のために、JMSの多孔板の孔の形状が固液分離性に及ぼす影響について解析して、円孔よりも縦スリット孔が有効であることを明らかにした。凝集剤としても、凝集沈殿汚泥からのリンの回収も考慮して、多用されているアルミニウム系に代わる新しい鉄系のPoly-Silicato-Iron(PSI)の有効性を検討し、凝集pHを6.5とすればAlと同等の添加濃度で同等の凝集効果を持つことを実証した。 (2) 生物膜の構造・機能解析による硝化機能の向上 下・廃水からの窒素除去を担う生物膜内の硝化細菌を対象として、16rRNAを標的とする蛍光遺伝子プローブを用いたFISH(Fluoresent In Situ Hybridization)法と共焦点レーザー走査型顕微鏡による画像解析を併用して、原水の有機物とアンモニア性窒素の濃度比(C/N)と生物膜形成時間が硝化細菌の種類と菌密度について研究した。アンモニア酸化細菌の優占種についての検討し、生物膜内には異なる生理特性を持つ様々なアンモニア酸化細菌が混在し、水質の変化に対応して菌相が入れ替わり、結果として生物膜のアンモニア酸化は安定して維持されることが明らかとなった。 (3) フミン質による膜ファウリング機構 フミン質と濁質が共存する高色度河川水で高度下水処理水に近い水質の千歳川をサンプルとして、回分膜ろ過実験によってUF膜のファウリング特性を明らかにした。高色度原水のUF膜ろ過では、フミン質が膜ファウリングの主原因物質である。膜ろ過で発現するファウリングに由来する抵抗を、(1)ケーキ層抵抗、(2)濃度分極層抵抗、(3)吸着抵抗、に分けてそれぞれを個別に定量化する方法を提案した。フミン質と濁質が共存すると高分子フミン質が大きな濁質粒子の間隙に入り込み、大きなケーキ層抵抗を発現する。膜細孔より大きい高分子フミン質によるケーキ層抵抗を、フミン質濃度の異なる濁質を含まない原水をろ過した場合の実験データを、Ruthのケーキろ過式を変形した式によって解析し、提案した膜ファウリング機構を検証した。 (4) 植物根分泌酸性ファスファターゼの遺伝子解析、機能評価 P処理を施したルーピンの根のRNAから、APaseをコードする2種類のcDNA,LASAP1およびLASAP2を単離した。LASAP1は細胞膜・壁に存在して根の表面に到達する有機態リン酸化合物を分解し、LASAP2は根から分泌されて有機態リン酸化合物を分解する機能をもつことが示された。
  • 膜を用いた新しい用廃水処理システムの開発
  • 医薬品の水処理過程中における動態
  • Development of a novel water /wastewater system using membrane technology

教育活動情報

主要な担当授業

  • 排水処理・再生工学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
  • 排水処理・再生工学特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • 下水工学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 雨水，汚水，管路，下水の水質，活性汚泥，栄養塩除去、汚泥処分
  • 分離工学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 分離，粒径，凝集，沈殿，吸着，膜
  • 流体工学Ⅰ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 流体，流れ，圧力，運動方程式，層流
  • 環境工学序論
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 環境問題の歴史，気候変動，SDGs，上下?道，?環境保全，室内環境，廃棄物処分，循環計画システム

大学運営

委員歴

  • 2017年 - 現在   日本膜学会   評議員
  • 2013年09月 - 現在   International Water Association (IWA)   Management Committee, Membrane Technology Specialist Group
  • 2012年06月 - 現在   International Water Association (IWA)   Chairman, Particle Separation Specialist Group
  • 2008年09月 - 2019年09月   日本水環境学会   「膜を利用した水処理技術」研究委員会委員長

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