Biological Nutrient Removal Using a Novel Five-step Continuous Flow Activated Sludge Process Technology

An anaerobic-anoxic/oxic (AA/O) five-tank biological process called five-step continuous flow activated sludge process (FSCFASP) was developed to force the oscillation of organic matter and nutrient concentrations in process reactors. The run scheme and schematic diagram of FSCFASP was described. The run cycle was divided into two symmetrical half cycles with eight periods during each cycle. The duration of each period was established according to biological process requirements. The optimal running times of the periods were 90, 60, 60, 30, 90, 60,6 0 and 30 min at the HRT of 16 h, air/water ratio of 35% and SRT of 21 day at the temperature range of 19–23 °C. The optimized system achieved 88.09±1.43%, 90.33±2.9%, 68.83±5.34% and 87.67±2.9% of the chemical oxygen demand, NH4-N, TN, and TP removal efficiencies, respectively, during a 11-month operation with the effluent meeting the Chinese sewage discharge standard GB18918-2002 (1evel A). Simultaneous nitrification and denitrification phenomena were observed in the tank one which is important to reduce the quantity of aeration and the duration of a next anoxic state. Compared with other existing technologies, this system achieved high nitrogen and phosphorus removal without equipment of sludge and mixed liquor return. Thus, it is effective for reducing energy consumption.