Performance of a hybrid SBR with fixed bed and suspended growth

A hybrid SBR system combined with fixed bed (media) and suspended growth zones was developed to improve both nitrogen and phosphorus removal. About 27% of the tank volume was filled with clay media to make a fixed bed in this system, and additional air was applied under the bed to wash the microbes from the media during the oxic stage to prevent the bed from clogging. This hybrid SBR system could eliminate the backwashing requirement for SBBR (sequencing batch biofilm reactor). This system showed a stable nitrification even at low temperature and shock load conditions. The specific reaction rates indicated the fixed bed zone had higher microbial activities for nitrification and denitrification, while the suspended growth zone had higher microbial activities for phosphorus release and uptake. In addition, the use of external sludge storage also increased both phosphorus and nitrogen removal. The effluent COD, nitrogen and phosphorus concentrations were respectively less than 15, 10.5 and 0.6 mg/L with weak sewage of 230 mg/L COD, 35 mg/L TKN and 5.3 mg/L TP.