Abstract
Control strategies for pre-coagulation and biological filtration processes are discussed with a pilot plant treating actual municipal sewage for 7 months including the winter season. Concentrations of SS, T-ATU-BOD, T-N and T-P in the effluent are less than 3mg/L, 5mg/L, 2mgN/L and 0.2mgP/L, respectively, and transparency is greater than 100cm, under total hydraulic retention time of 3.2h in the biological filtration part. Control of recirculation ratio by ORP measurement is proposed for good operation. Control of methanol addition by on-line nitrate measurement, control of aeration by on-line DO measurement, and control of backwashing by head loss measurement are successfully operated. They prove that easy-maintenance and cost-effective treatment is attainable.
