Impact of soluble organic compounds on permeate flux in an aerobic membrane bioreactor

The relative impact of mixed liquor suspended solids and soluble organic compounds on the permeate flux in an aerobic membrane bioreactor (MBR) were investigated during long-term operation. A statistical correlation analysis performed on data obtained over an approximately 700 day operational period revealed that permeate flux was strongly correlated to soluble organic compounds such as soluble sugars and proteins and was not correlated to total mixed liquor COD. Organic compounds with sizes less than 0.10 mum exhibited the strongest correlation to permeate flux. Specific filtration tests conducted on the MBR showed that the effect of soluble COD was most pronounced in the range of 110-210 mg l(-1). A critical level of soluble COD was established at 500 mg V after which point no correlation was present. The effluent quality remained high throughout the study at below 5 mg l(-1) total COD, indicating that the membrane was able to retain most organic compounds regardless of mixed liquor soluble COD content. It was concluded that MBR permeate fluxes are enhanced when operating at conditions where bio-degradation is improved and soluble organic compounds are reduced.