Impacts Of Nano-particles On Autotrophic Nitrogen Removal Process

At present,nitrogen removal from wastewater is still an urgent issue in environmental governance.However,the traditional nitrogen removal process now is unable to follow the increasingly stringent standard and satisfy the demand of wastewater reutilization.The autotrophic nitrogen removal process has been developed in recent years as an efficient and economic technology.It mainly includes the partial nitrification phase and Anaerobic ammonium oxidation?Anammox?phase.In this process,partial ammonia is oxidized to nitrite by ammonia-oxidizing bacteria?AOB?,and then the remained ammonia and produced nitrite were simultaneously transformed to nitrogen gas by anaerobic ammonia-oxidizing bacteria?AAOB?without any organic consumption.However,AAOB grows slowly and need a long time to get enrichment.Moreover,AAOB is very sensitive to the environmental conditions and easily influenced by the pollutants in wastewater.Therefore,this paper investigated the start-up strategy of the autotrophic nitrogen removal process and the inhibited mechanism of emerging pollutant-nanoparticles?NPs?on this process.In this paper,the sequencing batch reactors?SBR?was set and operated under a low dissolved oxygen?DO?concentrations??0.1 mg/L?,a high pH?7.8⁸.0?and room temperature.After the successfully start-up of partial nitrification,Anammox was then started-up without oxygen supply.During this process,the population of functional microorganisms was investigated.During the stable state of partial nitrification and Anammox process,the sludge was respectively taken out to carry out the batch experiments.For the partial nitrification sludge,the effects of Cu-NPs,CuO-NPs and CuO-NPs on sludge activity,ammonia nitrogen removal rate,the population of functional microorganisms and copper in sludge were investigated.For the Anammox sludge,the effects of different NPs on anaerobic ammonium oxidation rate,total nitrogen removal performance,extracellular polymeric substances?EPS?and microbial population in the sludge were studied.Moreover,CuO-NPs was selected as the representative NPs,and the effect the CuO-NPs with different particle sizes were investigated.Some conclusions have been cocluded:?1?The fast start-up strategy for autotrophic nitrogen removal process could be concluded as follows:The partial nitrification process was successfully started within 21days at room temperature,pH of 7.8⁸.0,DO?0.1 mg/L,and influent ammonia nitrogen of 200 mg/L.The Anammox process was started successfully within 35 days at room temperature,pH 7.8⁸.0,and ammonia nitrogen and nitrite concentration as 100 mg/L,respectively.The activity of the partial nitrification sludge after storage can quickly recover using anaerobic pre-culture in SBR-high aeration-continuous flow operation in MBR.In partial nitrification stage,the relative abundance of Nitrosomonas gradually increased and then decreased in the Anammox stage,while the Candidatus_Kuenenia increased.?2?The short-term inhibition threshold of Cu-NPs on partial nitrification sludge was30mg/L,and the long-term effect of 1mg/L Cu-NPs can reduce the ammonia nitrogen removal rate from 90 to 44.8%.Moreover,AOB was more sensitive to Cu-NPs than nitrite-oxidizing bacteria?NOB?.The short-term inhibition threshold of CuO-NPs on partial nitrification was 30mg/L,while that of the long-term decreased to 10 mg/L due to the adsorption and accumulation of nanoparticles in sludge.Without the addition of CuO-NPs,AOB could resist the acidic conditions?pH=6.5?.After the addition of NPs,AOB was significantly inhibited,while the low pH value done not intensify the inhibition of CuO-NPs.The acid condition increased the relative amount of Nitrosomonas but inhibited the removal of ammonia,so the suitable pH for the autotrophic nitrogen removal system was neutral to alkaline.?3?Results of the short-term effect of different NPs stated that CuO and ZnO NPs in 1⁵0mg/L have similar inhibition on the Anammox process,while TiO₂ in 1 mg/L promoted Anammox and significantly inhibited in 5²0 mg/L.No significant effex was observed to the TiO₂ in 50 mg/L.The direct toxicity to AAOB was CuO>ZnO>TiO₂,and the cumulative toxicity was CuO<ZnO<TiO₂.The results of the NPs with different particle size suggested that the smaller particle size made higher toxicity.Compared with the experimental result of Cu?II?,it can be concluded that the inhibition of CuO-NPs on Anammox was due to its nano effect rather than the effect of Cu?II?released by NPs.Candidatus_Brocadia was more tolerant to NPs than Candidatus_Kuenenia.