処理水循環DHSリアクターにおけるフェノールとアンモニア性窒素の同時除去

摘要

本研究では，DHS（Down-flow Hanging Sponge）リアクターを用いて，高塩分，高濃度フェノール・アンモニア性窒素含有廃水の処理を行い，処理水循環による脱窒の促進を試みた．3台の同形のユニットからなるDHSリアクターに人工廃水を供給し，基質の塩分を人工海水により10．9g-Cl／Lに制御した．全HRTを12時間に設定し，循環比を0～2．0の間で制御した（実験温度: 25℃）．流入水のアンモニア性窒素に対する流出水の硝酸性窒素，亜硝酸性窒素，アンモニア性窒素の回収率を求め，未回収分を脱窒率と定義して評価した・循環比0での脱窒率は20％程度であったが，循環比の上昇に伴い脱窒率も上昇し，循環比1.5で約58％となった，その後，循環比2．0で51％と減少した．また硝化および脱窒の活性試験とクローニング解析により，DHSリアクターの上流部において脱窒が卓越し，下流に向かうにつれて硝化が向上することが示された．さらにフェノールを電子供与体に利用するAzoarcusによる脱窒の寄与が示唆された．%A down flow hanging sponge reactor, constructed by connecting three identical units in series, was applied to the treatment of artificial wastewater containing phenol and ammonia under high salinity conditions (10.9 g-Cl~-/L). The theoretical HRT of each unit was 4 h (total HRT=12 h). To enhance denitrification by effluent recirculation, the effluent recirculation ratio was increased in increments ranging from 0.0 to 2.0. The concentration of total ammonia nitrogen, NO_2-N, and NO_3-N in the final effluent as a proportion of the total ammonia nitrogen in the influent were determined to calculate the unrecovered, or denitrification proportion. The denitrification proportion of the reactor was equivalent to 19.1 ± 14.1% with no effluent recirculation; however, this was increased to 58.6 ±6.2% when the effluent recirculation ratio was increased to 1.5. Further increasing the effluent recirculation ratio to 2.0 resulted in a decrease in the denitrification proportion to 50.9 ± 9.3%. Activity assays of nitrification and denitrification, as well as 16S rRNAgene sequence analysis, revealed that denitrification occurred primarily in the upper sections of the reactor, while nitrification increased in the lower sections of the reactor. Gene sequence analysis revealed that denitrification by Azoarcus-like species using phenol as an electron donorwere dominant.