Study On Methods For Membrane Fouling Control In Membrane Bioreactor

Membrane fouling is an important factor to baffle membrane bioreactor (MBR) widespread application. It has a great impact on the process performance such as energy consumption, membrane life and water production capacity. The aim of this research is to develop some methods that can mitigate membrane fouling with lower costs in order to popularize the MBR technology in China.In this study, the effects of operatin modes, powdered activated carbon (PAC) dosage, membrane performance enhancer (MPE) dosing, formation of granular sludge on membrane fouling were studied. Molecular weight distribution of pollutants in the influent, effluent, mixed liquor and membrane foulants were analyzed with the system combined with steric exclusion chromatography and refractive index detector. Pilot-scale aerobic membrane bioreactor (AMBR) and membrane sequencing batch reactor (MSBR) were compared in treating domestic wastewater under the same conditions. Two systems show good ability to withstand CODCr and ammonia nitrogen shock loading. MSBR has higher removal efficiency on total nitrogen than AMBR. Moreover, the membrane fouling rates of MSBR is slower than that of AMBR.Three parallel membrane bioreactors were operated to verify the effect of PAC dosage on membrane fouling for domestic wastewater treatment. The results show that the application of PAC cannot improve significantly the effluent quality. But it is effective in decreasing the content of extracellular polymeric substances (EPS) deposited on the membrane with PAC dosage less than 1 g/L. However, the membrane fouling caused by organics trends to increase when PAC dosage exceeds 1 g/L. Molecular weight distribution shows that the macro molecule (>10000 Dalton) organics in the mixed liquor also increases. Detailed studies on the effect of PAC dosage indicate that a PAC dosage of 0.75 g/L is the optimum in terms of keeping filtratin flux and decreasing operation cost.MPE can increase sludge size, retard the accumulation of cake layer on membrane surface and mitigate membrane fouling. But the effect is not obvious. The feasibility of using this agent needs further research.Aerobic granular sludge can improve effluent quality and retard membrane fouling. Some EPS combine with sludge floc and form granular sludge, which leads to a decrease of EPS in the mixed liquor and membrane. Moreover, granular sludge can reduce cake layer because of its larger size.The results of molecular weight distribution show that the effluent is constituted mainly with small molecule matters. It is important to control organics with small molecular weight in order to obtain good quality effluent. Many organics with molecular weight >10000 Dalton are accumulated in the reactor becaused of rejection by the membrane. Some of them are decomposed by microorganism gradually and organics with low molecular weight are formed at the same time.