Characteristics Of Nitrogen Removal And Membrane Fouling In Membrane Bioreactor Under Different Operation Conditions

The energy consumption of submerged membrane bioreactor is relatively low and the removal efficiency for COD is high.However,the removal effciency for total nitrogen(TN) needs improving.In recent years,new type biological nitrogen removal technologies provide theory foundation for improving nitrogen removal efficiency.In this research,reactor temperature was kept at 30℃and intermittent aeration mode was adopted.The influence of the dissolved oxygen(DO) concentration and aeration on/off time on short-cut nitrification and denitrification were investigated.The influence of extracellular polymeric substances(EPS) on membrane fouling were also studied.The main conclusions are as follows:(1) Set aeration on/off time at 5min/1min,change DO concentrations to 1 mg/L,2 mg/L,3 mg/L,4 mg/L and the TN removal efficiency is in the range of 11.28%～39.85%.The variation of DO concentration could not improve nitrogen removal efficiency significantly.The optimal TN removal efficiency and the least severe membrane fouling state could be obtained simultaneously.(2) Set DO concentration at 2 mg/L,change aeration on/off time to 5 min/1 min,20 min/4 min,20 min/10 min,10 min/5 min,5 min/2.5 min,the TN removal efficiency is in the range of 30.72%～69.68%.The variation of aeration on/off time could improve nitrogen removal efficiency substantially.Because DO concentration at the end of aeration-off period is below 1mg/L,the nitrogen removal efficiency was improved The optimal TN removal efficiency and the least severe membrane fouling state could not be obtained simultaneously.(3) Set DO concentration at 4 mg/L,variation of the aeration on/off time is the same with(2).TN removal efficienciy is in the range of 21.96%～34.16%.The variation of aeration on/off time could not improve nitrogen removal efficiency substantially. Because DO concentration at the end of aeration-off period is above 1.5mg/L,TN removal efficiency is only half of that when DO concentration is 2 mg/L.The optimal TN removal efficiency and the least severe membrane fouling state could not be obtained simultaneously either.(4) EPSs contributes more to membrane fouling than LB.Correlation indexes between polysaccharide in EPSs and membrane fouling rates is low while that of protein and humic acids are relatively high.The highest indexes is that of humic acids and its structure needs further study.