Modeling biodegradation characteristics of grey water in membrane bioreactor

The study evaluated the fate of grey water in a membrane bioreactor (MBR). It mainly involved the evaluation of system performance based on modeling biodegradation characteristics of grey water. The investigation was conducted on grey water using a pilot-scale MBR operated at a sludge age of 60 days. The system secured full removal of biodegradable organics with only 10 mg/L residual COD in the effluent, suitable for reuse. Model calibration of cyclic dissolved oxygen profiles fitted the experimental data and defined all related model coefficients with a lower maximum growth rate and lower hydrolysis rates compared with domestic sewage. Model simulation using process kinetics confirmed full removal of available biodegradable COD and generation of soluble microbial products. Significantly, higher soluble COD levels in the bulk liquid compared with the process effluent could be explained by means of cake filtration in the membrane, capturing larger fractions of soluble residual COD. Consequently, entrapment and partial biodegradation of soluble residual organics ensured the very low levels of effluent COD.

► MBR system provided partial biodegradation of the soluble residual COD.
► Nutrient limitation was prevented by selecting high SRT to secure high MBR efficiency.
► Model evaluation indicated complete removal of available biodegradable COD.
► Lower maximum growth and hydrolysis rates are defined as compared to domestic ww.