CHARACTERISTICS OF BACK-WASHING EFFLUENT IN A2 /O-BAF SYSTEM

A pilot-scale anaerobic /anoxic /short time aerobic ( A2 /O) -biological aerated filter ( BAF) combined process was set up to treat municipal wastewater． And the object of this study was to investigate the change of the effluent during and after back-washing of the BAF． Back-washing of the BAFs was carried out every 5 ～ 7 days and the procedure included three steps: air flushing，air and water combined flushing，water flushing，with lasting time of 10min，3min and 3min，respectively． This operation mode reduced the time of back-washing，saved the volume of water used for back-washing，and the operation was simple． The concentrations of SS，COD，ammonia nitrogen and TP increased firstly and then decreased during backwashing， showing that the suspended solids and detached biofilm were washed from the filter layer． By back-washing 1 ～ 2 days later， the effluent quality of BAF resumed to normal level． The removal performance of A2 /O-BAF process could be kept stable using the present backwashing strategy．