農業集落排水処理水が放流先河川水質および微生物叢に及ぼす影響評価

摘要

In this study, the impact of rural sewage effluent on the water quality of an agricultural water channel and rural river was investigated. Treated water samples from rural sewage, an agricultural water channel, and a rural river were analyzed. In addition, microflora analyses were conducted on the sediments and water samples from each location using the quinone profile methodology. The results revealed the critical need to study the impacts of treated sewage effluents on freshwater ecosystems. The nitrogen and phosphorus concentrations of water in the agricultural water channel increased downstream of the treated wastewater (TW) inflow. The annual average nitrogen and phosphorus concentrations in the TW were 7.33 mg L~(-1) and 1.83 mg L~(-1) higher, respectively, than those measured in the agricultural water channel upstream of the reclaimed wastewater inflow. Furthermore, a slight increase in the sediment microbial biomass, determined by the loss-on-ignition method, was observed in the treated water flowing into the agricultural water channel. It was clarified that rural sewage effluents with a high concentration of nutrients affect the microflora in the agricultural water channel, and, in particular, contribute to the increase in the amount of denitrifying bacteria.%農業集落排水処理水が農業用水路と農村部の河川の水質に及ぼす影響を明らかにするため,農業集落排水処理施設の処理水，処理水が流入する農業用水路および農業河川の水質分析を行った。また，キノンプロフアイル法により底質中および水中の微生物叢解析を行った。その結果，処理水(TW)中の溶存態窒素濃度と溶存態リン濃度の年間平均値は放流先の農業用水路と比較して，それぞれ7.33 mg L~(-1), 1.83mg L~(-1)高い濃度で流入しており，農業用水路の溶存態窒素濃度および溶存態リン濃度は，処理水流入後に増加することが明らかになった。また，農業用水路に流入する処理水によって底質の強熱減量あたりの微生物量にわずかな増加が認められた。栄養塩濃度が高い農業集落排水処理水放流による影響は農業用水路内の微生物叢を変化させ，特に脱窒菌の増加に寄与していることが明らかになつた。