| Artificial sweeteners(ASs)have been widely used in food,beverages,drugs and pharmaceuticals and personal care products(PPCPs).They have been listed as a kind of emerging environmental contaminants due to their high residual concentrations,high frequencies of detection and durability in water environment.Wastewater treatment systems are main gathering locations for ASs spread into the environment.The distributions,environmental behaviors,ecological risks and control strategies of ASs have become the focus of research.But there are few studies on the effects of ASs on wastewater biological treatment systems.In this study,four popular ASs(acesulfame(ACE),sucralose(SUC),cyclamate(CYC)and saccharin(SAC))were chosen as typical ASs.To evaluate the effect of ASs on activated sludge,they were introduced individually or in mixture to indoor simulation sequencing batch reactors(SBRs)fed by synthetic wastewater or real wastewater.The effects of ASs on water quality,microbial activity and microbial community structure were analyzed.ACE removal factors were conducted by batch tests and simulation reactors.The main results are as follows:1.The effect of ASs on water quality of SBRs:when SBRs were operated by synthetic wastewater,COD,NH4+-N and TN removal rates appeared unchanged after adding ASs(p>0.05).Results showed that ACE,CYC and SAC were removed in the mixed ASs and individual ASs.SUC was persistent and removal of SUC ranged from 20.27%to 33.90%.2.The effect of ASs on microbial activity:when SBRs were operated by synthetic wastewater,ASs promoted the secretion of extracellular polymeric substance(EPS).ATP concentrations and live ratios of microorganism declined significantly(p<0.05).Compared to the control,Triphenyl tetrazolium chloride-dehydrogenase activity(TTC-DHA)decreased significantly(p<0.05)in the experiment tests.The target ASs had no significant effect on ammonium monooxygenase(AMO)and nitrite oxidoreductase(NOR)activities.3.The effect of ASs on microbial community structures:when SBRs were operated by synthetic wastewater,ASs caused evident effect on microbial community structures.The dominant bacteria of activated sludge in phylum level were Proteobacteria,Bacteroidetes and Chloroflexi.Compared to the control,the abundances of Proteobacteria decreased at ASs selective pressure,and the abundances of Gammaproteobacteria declined more obviously.On the contrary,the abundances of Bacteroidetes and Chloroflexi were enriched with the addition of ASs,and the mixed ASs had more evident effects than the individual ASs.The dominant bacteria of activated sludge in genus level were Thauera,Ignavibacterium and Zoogloea,and the abundances of bacteria were significantly increased at ASs selective pressure.The abundances of Nitrosomonas and Nitrospira had no obvious change,and the change trends were similar with that of nitrification enzyme(AMO and NOR)activities.4.The effect of ASs on activated sludge in real wastewater:when SBRs were operated by real wastewater,COD,NH4+-N and TN removal appeared unchanged after adding ASs(p>0.05).At stable stage of SBRs,the removals of ACE,CYC and SAC were similar with their removal in synthetic wastewater,while SUC removal showed negative growth(-12.98±2.04%).Compared with activated sludge in synthetic wastewater,the performance of activated sludge in real wastewater was relatively poor.In real wastewater,ASs promoted the secretion of EPS,whereas TTC-DHA,ATP concentrations and live ratios decreased.With the addition of ASs,microbial community structures of activated sludge changed,but the degrees of change were significantly weaker than the degrees of change in synthetic wastewater.It indicated that activated sludge was much easier to resist the adverse effect of ASs on microorganism performance in real wastewater.5.The study on ACE removal in activated sludge:ACE removal in simulation SBRs was significantly greater than that in the wastewater treatment plant.The effects of hydrolysis and volatilization on ACE removal were negligible.Sludge sorption played a minor role in the elimination of ACE.Therefore,ACE increased removal in simulation SBRs was due to microbial enhanced biodegradation.The dissolved oxygen of activated sludge had no effect on ACE removal,and it could be degraded in aerobic and anoxic activated sludge.Nitrification cometabolism had no significant effect on degradation of ACE.Solids retention time(SRT)of reactors had obvious effect on ACE removal.When SRT was 20 d,ACE removal reached maximum.Moreover,biodegradation of ACE in SBRs followed the first-order model. |
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