嫌気性膜分離法(AnMBR)を用いた人工下水処理性能に及ぼす温度の影響

摘要

メタンガス回収や汚泥生成量削減の観点から，嫌気性処理と膜分離技術を組み合わせた嫌気性膜分離法(AnMBR)が注目されている。本研究では段階的に温度を下げて，人工下水を用いた連続処理実験を行い，処理性能や物質収支，膜性能に及ぼす温度の影響を評価した。HRT12hにおいて，25,20,15℃での処理水の化学的酸素要求量（COD)及びCOD除去率はそれぞれ18·17,40mg·L~(-1),96,96,92%であり，低温処理が可能であることが示された。物質収支においてメタンガス回収率は15てで，10%前後低下した。膜性能面において温度低下により膜圧増加速度が増加し，その要因として有機物の目詰まりが考えられた。ケーススタディより，AnMBRは従来の下水処理プロセスと比べて良好な水質，効率の良いエネルギー回収，汚泥生成量の削減が同時に実現する可能性が示唆された。%Anaerobic membrane bioreactors (AnMBRs) in which anaerobic digestion and membrane separation are combined have recently been attracting attention, because they can recover methane and reduce sludge production in wastewater treatment. In this study, a laboratory-scale AnMBR for treating synthetic sewage was continuously operated with lowered the temperature gradually from 25 to 15℃ to investigate the effect of temperature on the treatment performance, mass balance, and membrane performance. At hydraulic retention time (HRT) of 12 hours, the chemical organic demand (COD) concentration of the effluent and COD removal at 25, 20, and 15℃ were 18,17, and 40 mg·L~(-1) and 96, 96, and 92% respectively. Concerning the mass balance, no difference in the conversion ratios of methane including dissolved methane was seen, but the recovery ratio of methane gas at 15℃ was about 10% lower than those at 25 and 20℃. Regarding the membrane performance, the rate of trans-membrane pressure was increased by lowering the temperature, and the reason increasing the membrane pressure was thought to be the blocking of pores by organic matter from microbial metabolic products. The AnMBR was expected to successfully produce clean water, recover energy efficiently, and reduce the amount of sludge produced compared with traditional sewage treatment.