鶏舎洗卵所排水に適用した間欠鉛直流式人工湿地の開始3年間の浄化効果

摘要

We evaluated the processing capacity of a water purification system for low-organic-content wastewater from a poultry grading and packing facility. The system comprised vertical-flow intermittent feeding constructed wetlands connected in series. The BOD (Biochemical Oxygen Demand) of the water treated in the first stage was 6.8 mg·L~(-1). After stabilization at the facility, it was about 2-3 mg·L~(-1), for a decrease in BOD of 90% or more. SS (Suspended Solid) and BOD were removed in Wetland 1, where coarse particles were used as filter material, but D-BOD (Dissolved BOD) removal tended to occur in Wetland 2, where fine particles were used. The NH_4-N concentration at each survey point was low, but the NO_3-N concentration tended to increase with downstream flow. NH_4-N generated by mineralization was rapidly nitrified. The average OTR (Oxygen Transfer Rate) value was 6.5 g·m~(-2)·day~(-1), which is much less than 28 g·m~(-2)·day~(-1), the standard in the United States and Europe, but the upper load limit was not confirmed. Filling the wetlands with water took longer in winter than in summer. The decomposition of solid organic materials is delayed by clogging in winter, but the water temperature rises in summer, suggesting an improved discharge capacity owing to organic matter decomposition.%鶏舎洗卵所の低濃度有機性排水処理において，間欠鉛直流式人工湿地を2基直列に用いた水質浄化システムの処理能力を評価した。初期に6.8mg·L~(-1)であった処理水のBOD(生物化学的酸素要求量)値は，安定後は2～3mg·L~(-1)前後で推移し，90%以上の減少率を示した。SS(懸濁物質)やBODの除去はろ材の粒径が粗い湿地1で進み，D-BOD(溶存態BOD)の除去は細粒のろ材を用いた湿地2で進む傾向が見られた。各測点のNH_4-N濃度は微量であるが，無機化によって生じたNH_4-Nが迅速に硝化され，流下に伴ってNO_3-Nが増加した。OTR(酸素移動速度)平均値は6.5g·m~(-2)·day~(-1)であり，欧米の基準とされる28g·m~(-2)·day~(-1)より低く，負荷量の上限は確認できなかった。湿地内の滞水時間は，冬期は夏期よりも長かった。冬期間は固形有機物の分解が遅れて目詰まりが生じるものの，夏期にかけて水温が上昇し有機物の分解が進行することにより，流下能力の改善が示唆された。