Anaerobic Membrane Bioreactor Treatment Of Municipal Wastewater: Process Optimization, Membrane Fouling Control And Mechanism Of Microorganism

The anaerobic membrane bioreactor has been widely applied in municipal wastewater treatment in recent years.It has many advantages such as high effluent quality,energy production,low sludge yield,small footprint,etc.,and it has become a promising water treatment technology.Membrane fouling is the main factor restricting the engineering application of anaerobic membrane bioreactor.At present,some researchers have studied the operation parameters optimization and membrane pollution control strategy of anaerobic membrane bioreactor.However,few studies have been conducted to invesitage the reactor optimization and membrane fouling control from the perspective of microbial community structure and function analysis.In this study,the optimization of operating parameters in the process of treating municipal wastewater by anaerobic membrane bioreactor and the feasibility of real wastewater treatment were carried out.The membrane fouling was effectively controlled by biofilter,and the anaerobic treatment system was systematically studied.Microbial community structure changes in the carrier filter system and membrane filtration system were analyzed to reveal the relationship between pollutant removal,membrane fouling and community turnover in the treatment of municipal wastewater by anaerobic membrane bioreactors.The main conclusions are as follows:(1)Three sets of anaerobic membrane bioreactors,which have different hydraulic retention time(HRT)were operated.It was found that the HRT affects pollutant removal,gas production activity and membrane fouling.The optimal HRT is 12h.The COD of the effluent of the reactor is less than 80mg/L,the removal efficiency is over 80%,the methane yield is 0.19 LCH4/gCOD,and the membrane fouling period is 28 days.The effects of proteins in soluble microbial products(SMPp)and extracellular polymeric substances(EPSp)are different in different periods of the same membrane pollution cycle.The rate of accumulation of EPSp and SMPp on the surface of the membrane is the main cause of membrane fouling.There is no significant difference between the treatment efficiency of synthetic wastewater and real wastewater,and the aggravation of membrane fouling during operation is a difficult problem to be solved in the application process.(2)Two sets of biofilters were incorporated to the AnMBR systems to invesitigate the removal of pollutants and controlling membrane fouling.It was found that the performance of the two biofilters have great difference.The tandem activated carbon filter has better effect on the enhanced removal of effluent organic matter than the ceramsite filter.The COD of effluent is less than 30mg/L,and the removal rate of COD reaches 95%.At the same time,the activated carbon biofilter significantly prolonged the operation cycle of membrane fouling,and the mitigation effect of ceramsite on membrane fouling was not obvious.The activated carbon biofilter slows the development of membrane fouling by improving the inlet water quality conditions of the membrane unit and slowing the accumulation rate of EPSp and SMPp on the membrane surface.(3)Proteobacteria plays an important role in anaerobic treatment of municipal wastewater.Methanosaeta,Bacteroides,Sphingomonadaceae,Chlorobiaceae,Clostridium,Rhodanobacter and Bacteroidales are key microorganisms for anaerobic treatment of municipal wastewater.Firmicutes occupies a high relative abundance in biofilters,which is higher than that in conventional filters,and the abundance in activated carbon filters is higher than that in ceramsite filters,and the relative abundance can reach 30%and 15%,respectively.Firmicutes play an important role in the removal of contaminants from biofilters.The number of unique operational taxonomic units(OTUs)of activated carbon biofilter and ceramsite biofilter is 93 and 16,respectively,and the number of unique OTU in activated carbon biofilter is significantly higher than that of ceramsite biofilter.Moreover,the OTU distribution unique to activated carbon biofilters is much broader than that of ceramsite.Therefore,the number and types of key microorganisms in the activated carbon biofilter are relatively abundant.Under low load conditions,the degree of membrane fouling is relatively low,and the abundance of Actinobacteria is relatively low,indicating that Actinobacteria has a greater impact on membrane fouling.High loads can lead to increased abundance of Azospirillum,Pseudomonadaceae,Pseudomonas,Arenimonas,and Bacillus in the membrane module,which in turn leads to increased membrane fouling.The tandem activated carbon biofilter can reduce the abundance of Firmicutes and Actinobacteria on the membrane module,thereby alleviating membrane fouling.The tandem biofilter can significantly affect the microbial composition of the membrane module.Most of the relatively abundant abundance microorganisms have decreased to some extent when not connected to the biofilter,including Rhodobacter,Azospirillum,Pseudomonas,Cloacibacterium,Bacillus,Thermomonas,Paracoccus,Pseudomonadaceae,Carnobacteriaceae,Sphingomonadaceae and Xanthomonadaceae.