Research On Membrane Fouling In A Submerged Membrane Bioreactor Under Different COD/N Ratios

Two submerged membrane bioreactors (MBRs) were operated for 130 days under different COD/N ratios to investigate the effect of COD/N ratio on membrane fouling. Different fouling rates were observed under various COD/N ratios.The composition and characteristics of bound extracellular polymeric substances (EPS) and soluble microbial products (SMP) under each COD/N ratio were examined. To identify the main contributor to membrane fouling under each COD/N ratio and the corresponding relationship between each fraction of fouling with SMP or EPS, we conducted hydraulic resistance analyses of the membranes at the end of each COD/N ratio experiment, and we found that bio-cake resistance (Rc) is the main contribute of membrane fouling. The concentration and carbohydrate/protein ratio of EPS and SMP, which govern the fouling rate, were higher under high COD/N ratios when COD/N ratio was below 5.1. Thus under these COD/N ratios, the fouling rate increased with COD/N ratio increase. Because NH4+-N replaced divalent cations in bound EPS, high concentrations of SMP and low concentrations of EPS were observed in the system under a COD/N of 5.1. The fouling rate was determined by the balance between the SMP and EPS factors under this COD/N ratio.To study the specific role of these two factors in formation of bio-cake under different COD/N ratios, the EPS and SMP of bio-cake suspension were examined to investigate the characteristics of bio-cakes. The considerable fluctuation that occurred in EPS under different COD/N ratios indicates that the EPS factor was more important in controlling the overall fouling rate and formation process of bio-cakes. Additionally, the SMP factor, which was less affected by COD/N ratio, also caused high fouling rates even though the EPS of sludge was low under a COD/N ratio of 5.1.