Analysis Of Membrane Fouling Behavior And Key Factors In Membrane Distillation Bioreactor

Membrane Distillation Bioreactor?MDBR?is a novel reactor that is applied in wastewater treatment and wastewater reuse.Based on the biotechnology and membrane distillation process,instead of the biochemical stage and the advanced treatment stage,MDBR process has a lot of advantages,which are higher quality effluent,less running processes,smaller area covered,less residual sludge produced,and so on.Because of its temperature-specific driving conditions,MDBR's microbial metabolism and membrane fouling behavior are different from the conventional membrane bioreactors?MBRs?.In this project,simulated wastewater was used to study the contaminants'removal performance,sludge mixture properties,microbial community variation and their relationship with membrane fouling during the continuous operation of MDBR,which would provide reference for the future process optimization and operation of MDBR.The main conclusions are listed as followed:?1?Membrane distillation bioreactors were used to treat the simulated wastewater.The removal rates of COD and ammonia nitrogen reached 97%and 93%under different temperature conditions?30°C,40°C,and 50°C?,respectively.The effluent water quality was clarified and the conductivity was reduced to 15?s/cm below.The membrane fouling of MDBR was severe,and membrane flux decreased by 50%,65%and 80%after 20 days of operation.According to the membrane fouling resistance analysis,it was found that the surface of the membrane gradually formed a stable pollution layer,and the layer became thicker at a higher temperature,whose reason may be the change of metabolic activity of the microorganism at different temperatures.In addition,the main components of the membrane fouling layer were tested mainly including proteins and polysaccharides,which were highly homologous to the soluble microbial metabolites in the reactor.?2?The membrane distillation bioreactor was operated at 40°C under the different HRT conditions?40h,48h,and 60h?.The removal rates of COD and NH₄⁺-N in MDBR were above 99%and 97%,respectively.The conductivity rate fell less than 10?s/cm,and the membrane fouling was observed.Membrane fluxes were decreased by 58%,46%and 56%,respectively,after10 days.The membrane fouling was relatively lighter on 40h than that on 48h and 60h,which may be related to the shorter organic load of HRT.High levels of COD in sludge supernatants were associated with the longer endogenous respiration of HRT and release of more organic pollutants.The chemical analysis of the membrane fouling layer showed that the proteins in the pollutants were mainly derived from the soluble microbial metabolites,and the polysaccharides and humic acid-like substances mainly from the soluble microbial metabolites and extracellular polymers.?3?The microbial community structure in the reactor and membrane fouling layer under different temperature and HRT conditions were analyzed,and the relationship between microbial community structure and membrane fouling were studied.The studies have shown that temperature had a great influence on the microbial species.Compared with 30°C and 40°C,the microbial community structure had a distinct change at 50°C.In addition,the microbial species in the membrane pollution layer were significantly higher than those in the reactor.This result may be related to the higher content of protein and polysaccharide on the surface of the membrane.With the temperature rising,proteobacteria proliferative?and?gradually increased,indicating that proteobacteria could accelerate the membrane fouling.The microbial communities in the reactor and membrane contaminated layers were not significantly different at the same HRT time.There was a small difference in microbial populations in the reactor and membrane contaminated layers at 40 h and 48 h.The number of microorganisms at 60 h varied greatly.Besides,with the HRT increasing,Proteobacteria of?and?more likely became the dominant species,causing more serious membrane fouling.