MBRを用いた高度処理化に関する実証的研究: サテライト処理への槽外型MBRの適用について

摘要

An evaluation was carried out regarding the application of a membrane bioreactor (MBR) in a satellite treatment system in which sewage is drawn off and treated at a pumping station, etc. before arriving at the wastewater treatment plant and the effluent is re-used. In the evaluation, a satellite MBR demonstration plant was installed at Miai Pumping Station, Kinuura Eastern Regional Sewerage System, Aichi Prefecture (separate system), and continuous treatment experiments were carried out to obtain demonstration data regarding the plant's treatment performance and stability. As a result, with regard to performance of the side-stream MBR plant using a ceramic membrane, it was confirmed that stable operation at a maximum membrane filtration rate of 3.2 m/d is possible; and in experiments with fluctuating effluent volumes that took into account fluctuation in reclaimed wastewater demand, it was confirmed that stable nitrogen removal performance, etc. is achieved even in operation at HRT 4h. When various standard values and effluent qualities appropriate to the intended reuse application were compared, as well as confirming that effluent from the satellite MBR can be used without further treatment for toilet flushing, sprinkling, and landscape use, it was confirmed that with the addition of a small amount of ozone treatment it can also be used as water for recreational use. Also, the norovirus removal rate was 2.5 log - 3.7 log or above for GI and 2.1 log - 5.0 log or above for GII, confirming that a high removal rate can be achieved compared to existing processes such as the standard activated sludge process. The evaluation revealed that, if the effluent volume of the satellite MBR is large compared to the pumping station influent, there is an increase in variation in concentration of solids and flow rate before and after the pumping station and, depending on the situation, it may be necessary to review the design values of the wastewater treatment plant on the downstream side of the pumping station. Also, requirements for residual chlorine concentration for effluent when constructing a circulation stream using satellite MBR effluent were investigated using batch tests.%下水処理場に至る前の下水をポンプ場等で取水して処理を行い，処理水を再利用するサテライト処理に，槽外型膜分離活性汚泥法（MBR）を適用する検討を行った．検討にあたって，サテライトMBRの実証設備を愛知県衣浦東部流域下水道見合ポンプ場（分流式）に設置して連続処理実験を行い，設備の処理性能と安定性について実証データを取得した．その結果，セラミック膜を使用した槽外型MBRの設備性能は．最大3．2m／dの膜ろ過流束で安定運転が可能であることを確認し，下水再生水の需要変動を考慮した処理水量変動試験では，HRT4hでの運転においても安定した窒素除去性能等が得られることを確認した．再利用用途先に応じた各種基準値と処理水質を比較検討したところ，水洗用水，散水用水，修景用水に対しては，サテライトMBRの処理水がそのまま活用できることを確認したほか，少量のオゾン処理の追加によって，親水用水として利用しうることを確認した．また，ノロウイルスの除去率は，GIで2．5log以上～3．7log以上GⅡで2．1log以上～5．0log以上となり，既存の標準活性汚泥法等のプロセスに比べて高い除去率が得られる可能性があることを確認した．ポンプ場前後における，流量，固形物濃度の変化は，サテライトMBRにおける処理水量が，ポンプ場流入水に比して多い場合は大きくなり，場合によっては，ポンプ場下流例の下水処理場の設計値を見直す必要があることを明らかにした．さらに，サテライトMBR処理水を用いて，循環せせらぎ水を構築する際の処理水の残留塩素濃度の必要条件を，バッチ実験より検討した．