Study On Process Optimization And On-line Chemical Backwashing Of Inverted A~2O-MBR System

Membrane bioreactor(MBR)combines membrane filtration and activated sludge process.It has attracted wide attention by its small area,good treatment effect,high sludge concentration and low excess production of sludge.However,high sludge concentration also leads to serious membrane fouling,which limit the further application of MBR.This experiment explored how to alleviate membrane fouling from the operation optimization of inverted A~2O-MBR process.By analyzing the effects of different effluent fluxes(15,20,25 LMH)and returning mixed liquid ratio(50%,100%,150%)on reactor operation performance,sludge properties,EPS composition and characteristics,and membrane fouling,the optimal effluent flux and returning mixed liquid ratio were optimized.The optimized effluent flux and returning mixed liquid ratio were applied to the MBR system,and on-line NaClO backwashing was carried out to investigate the effect of on-line NaClO backwashing on the treatment efficiency of the system.The diversity of microbial populations in the reactor and membrane before and after NaClO backwashing was studied by high-throughput sequencing to evaluate the synthesis of microbial communities in the MBR system by on-line NaClO backwashing.The purpose is to provide basis and reference for the application of on-line NaClO Backwashing in practical engineering.The main conclusions are as follows:(1)The treatment efficiency of COD and ammonia nitrogen in the three periods of flux 20LMH is best.The analysis of TMP shows that the shorter the period of membrane pressure difference is,the higher the membrane fouling rate is.EPS analysis showed that the EPS concentration of cake layer sludge was the lowest at the operation stage of flux 20LMH,while the EPS concentration and polysaccharide concentration were the highest at 25LMH,and the membrane fouling was the most serious,which was consistent with TMP analysis results;the total resistance of membrane fouling was the smallest at flux 20LMH and the largest at flux 25LMH;comprehensive comparison showed that the effluent effect was better when effluent flux was 20LMH and the membrane fouling was the best.(2)The mixed liquid reflux ratio of 50%,100%and 150%has better effect on COD,ammonia nitrogen and total nitrogen treatment.The change of mixed liquid reflux ratio has no obvious effect on COD removal,but when themixed liquid reflux ratio is too large,the removal effect of ammonia nitrogen and total nitrogen is not good.The analysis of TMP shows that the larger the mixed liquid reflux ratio,the shorter the period of pressure difference across the membrane and the more serious the membrane fouling.The EPS of aerobic tank sludge and cake layer sludge was analyzed.The results showed that the EPS concentration of aerobic tank sludge and cake layer sludge increased with the increase of mixed liquid reflux ratio,especially the polysaccharide concentration.The total resistance of membrane fouling is the smallest when the mixed liquid reflux ratio is 50%,and the largest when the sludge reflux ratio is 150%.Comprehensive comparison shows that the reactor effluent effect is the best when the mixed liquid reflux ratio is 50%,and the membrane fouling is the slowest.(3)On-line NaClO backwashing of inverted MBR system shows that on-line chemical backwashing has little effect on system operation;monitoring of TMP and EPS of cake layer shows that membrane fouling rate and EPS concentration increase after on-line chemical backwashing;Chao index and Simpson index show that the microbial population of aerobic tank and cake layer sludge is mainly Proteobacteria,followed by Proteobacteria.Bacteroidetes;after online chemical backwashing,the population abundance of sludge in cake layer increased slightly,the diversity of microorganisms decreased significantly,the relative abundance of Proteus and Bacteroidetes in aerobic tank sludge changed little,but the composition of sludge in cake layer changed obviously,especially Proteus,which was resistant to chlorine disinfectant,increased from 53.41%to 77.84%.However,Bacteroides decreased from33.44%to 14.51%.Those microbial species that can tolerate NaClO treatment may be the main reason for aggravating membrane fouling.