EFFECTS OF SHORT SOLIDS RETENTION TIME ON PERFORMANCE AND MEMBRANE FOULING OF SUBMERGED ANOXIC/OXIC MEMBRANE BIOREACTORS

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were operated simultaneously to study the influence of SRT on the biodegradation performance and membrane fouling. Excellent TCOD removal of more than 95% and complete nitrification were observed in all the four systems. However a longer SRT operation was observed to improve the denitrification efficiency. The total nitrogen removal efficiency was less than 67% for SRT less than 10 days but 77% for SRT of 20 days. Membrane fouling was first observed in the 3 days SRT operation and its fouling rate was more rapid than that observed at 5 days SRT. No fouling was observed in the 10 days and 20 days SRT systems during the 136 days of operation. It was found that MBR system operated at shorter SRT tended to accumulate more TOC or soluble microbial products (SMP) in the mixed liquor supernatant. Membrane rejection of carbohydrate originated from SMP was found to be more significantly influenced by the operating SRT as compared with the membrane rejection of protein. Thus carbohydrate in the mixed liquor supernatant could be the main membrane foulant of MBR operating at short SRT.