下水2次処理水の2層ろ過における処理性能に及ぼす砂粒径の影響と砂層閉塞パターン

抄録

Experiments on a proposed dual-media filterwere conducted to investigate the effect of sand size on its perfomance in direct filtration with coagulation for secondary wastewater effluent.Aluminum sulfate was used as a coagulant to remove soluble substances and improve turbidity removal.
The results obtained are summerized as follows:(1) The over-all removal efficiency of the filter for turbidity, color and phosphate did not change too much with sand size at the filtration rate of 120m/d, but decreased with an increase in sand size at 240m/d and over.(2) On condition that the criteria for the limiting head loss and for the limiting filtrate turbidity were 3m and 5mg/l, respectively, the length of the filter run depended on the head loss limit regardless of the filtration rate in the case of a sand size of 0.59-0.71mm. In the case of sand size larger than 0.85-1.00mm, it depended on the head loss limit at 120m/d and on the filtrate concentration limit at 240m/d and over.(3) The optimum sand sizes were larger than 1.00-1.20mm at 120m/d and 0.71-0.85mm at 240m/d and over.(4) The reduction of porosity with specific deposit (mass of deposit/unit filter volume) did not change too much regardless of sand size, but became smaller with an increase in filtration rate.