| Sewage as a major reservoir for human enteric viruses and is also a significant medium for virus transmission.Untreated or inadequately treated sewage viruses entering natural water environments can lead to outbreaks of infectious diseases,posing a serious threat to human health.MBR are divided into two operating processes: aerobic membrane bioreactors(AeMBRs)and anaerobic membrane bioreactors(AnMBRs).Clearly,there are significant differences between AeMBR and AnMBR in terms of mixed liquor characteristics,microbial species and metabolites,as well as the composition of membrane fouling.These differences may result in variations in virus removal efficiency and removal mechanisms between AeMBR and AnMBR.In this study,under the same operating conditions,using bacteriophage MS2 as a model virus,we investigated the virus removal performance of AeMBR and AnMBR in wastewater.We compared the variations in virus removal between the two reactors and explored the differences in virus inactivation in the mixed liquor,virus adsorption by sludge,and virus retention by the membrane.Additionally,the adsorption mechanism of viruses by extracellular polymeric substances(EPS)and soluble microbial products(SMP)was further investigated.The main findings and conclusions are as follows:(1)AeMBR and AnMBR both achieve good virus removal performance in wastewater,with virus removal rates reaching a 3 log reduction.However,the removal patterns of the two differ,with AeMBR rapidly achieving a 2-log reduction in virus removal,while AnMBR requires 60 days to achieve the same reduction.This is because viruses are more prone to adsorption on the membrane surface of AeMBR,while the membrane of AnMBR gradually enhances its virus retention capacity with the formation of membrane fouling.After chemical backwashing,the virus removal rate decreases by 0.8 log,and the decreased removal rate rapidly recovers as membrane fouling accumulates again.AeMBR has a shorter recovery time.(2)The solid-phase virus concentration in the mixed liquor of aerobic and anaerobic sludge is 1 log higher than the liquid phase.The solid phase of both sludges adsorbs 90% of the viruses in the mixed liquor.The virus adsorption capacity of aerobic and anaerobic sludge,per unit mass,is 8.59 and 10.11 log PFU/g SS,respectively.The anaerobic sludge exhibits a stronger virus adsorption capacity.This may be due to the lower electrostatic repulsion between anaerobic sludge and viruses compared to the electrostatic repulsion between aerobic sludge and viruses.Anaerobic sludge exhibits shorter adsorption equilibrium time and higher equilibrium adsorption capacity for viruses compared to aerobic sludge.The soluble microbial products(SMP)in the activated sludge play a major role in virus adsorption.(3)The decay rate of viruses in the liquid phase of aerobic and anaerobic sludge mixture is higher than in the solid phase.The solid phase of sludge protects the adsorbed viruses from decay.The decay rate of viruses in aerobic sludge mixture is higher than in anaerobic sludge mixture.Microbial metabolites are the key factors in the decay of viruses in the mixture,and the metabolites produced by aerobic sludge have a stronger effect on the decay of viruses.(4)There is no significant correlation between TMP(Transmembrane Pressure)and virus removal efficiency in AeMBR,whereas AnMBR shows a significant correlation between TMP and virus removal efficiency.Membrane fouling is the main factor affecting virus removal in AnMBR,but it cannot be used as an evaluation indicator for virus removal in AeMBR.The cake layer in the various components of membrane fouling is the primary contributor to virus retention in both types of membrane bioreactors for virus removal.In AeMBR,the unit membrane resistance of irreversible fouling and pristine membrane components contributes the most to virus retention efficiency.In AnMBR,the unit membrane resistance of pore-clogging organic fouling in membrane fouling contributes the most to virus retention efficiency. |
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