Primary Treatment of Domestic Wastewater and Wet Weather Flow Using High Rate Up-flow Filtration System with Floating Media in Mega City Seoul

A municipal wastewater treatment plant (MWWTP) in City of Seoul has been discharging 58% of annual total biochemical oxygen demand (BOD) loads during the wet season. The City of Seoul's master plan is to construct wet weather flow treatment facilities for total capacity of 9,750,000m3/d (2,574 MGD) by 2026. Therefore, the City of Seoul is in the process of constructing BKT's high rate up-flow filtration system (321 MGD) in order to reduce BOD and Suspended Solids(SS) loads for wet weather flow (WWF) and combined sewer overflows (CSOs) for the first stage of master plan. A demonstration study was carried out with the up-flow, high rate filtration system as a primary and WWF treatment to evaluate the optimal linear velocity and its conditions in dry and wet seasons, respectively. A pilot test is performed to evaluate the optimal coagulant dosages, backwashing cycle, and flowrate that comply with the City's water quality requirement. A pilot test evaluated the system performance under varying operating conditions. The average removal efficiencies were 45.3~49.7% for SS and 35.0~40.1% for BOD with 10~20 m/hr linear velocities for dry season without coagulant addition. During the wet season, coagulant was added to enhance the removal efficiency and the average removal rate was over 80% and concentrations were measured less than 40 mg/L for both SS and BOD at 20 m/hr linear velocity. This high rate up-flow filtration system with known as BKT's Biofiltration (BBF) could meet the City of Seoul's water quality goal to handle three times the design flow rate (3Q) and reduction of BOD to ≤40 mg/L with coagulant addition for WWF.