Study On The Effects Of Metalions And Sulfadiazine On The Performance Of Completely Autotrophic Nitrogen Removal Over Nitrite(CANON) System

The completely autotrophic nitrogen removal over nitrite(CANON)system has a broad application prospects in the field of wastewater treatment with the advantanges of high efficiency,economy,and energy saving.Pharmaceutical wastewater which was a type of high ammonium industrial wastewater,and nitrogen removal is urgent nowaday.However,the residual of antibiotics and metalions in the wastewater would affect the activity of functional microorganisms activities in the CANON system.Therefore,the effects of manganese(Mn²⁺),zinc(Zn²⁺)and copper(Cu²⁺)on the nitrogen removal efficiency of CANON system were explored,and the effect mechanism was revealled through analyzing the microbial community structure,functional microorganisms abundance,extracellular polymeric substance(EPS)and the distribution characteristics of metalions.At the same time,the feasibility of simultaneous removal of ammonium and sulfadiazine(SDZ)by CANON system under the exposure of SDZ was investigated,the effect mechanism was analyzed through variations in microbial community structure and expression of key functional genes,and antibiotic resistance genes(ARGs)under SDZ pressure were also explored.Furthermore,the occurrence and expression of ARGs and the biological toxicity of SDZ degradation products were investigated.On this basis,the application of CANON system with treating wastewater containing SDZ and ammonium was assessed.The main results are presented as follows:(1)For short-term exposure,all the three elements could improve the nitrogen removal rate(NRR)and the optimal concentrations were 2.0,2.0 and 0.5 mg/L for Mn²⁺,Zn²⁺and Cu²⁺,respectively.Accordingly,the NRR were enhanced 54.62%,45.93%and 44.09%.The long-term experiments were carried out in lab-scale sequencing batch reactors.The surprising results showed that only Mn²⁺addition could enhance the long-term nitritation-anammox process,and the NRR increased from 0.35±0.01 kg N/m³/d(control,no extra trace element addition)to 0.49±0.03 kg N/m³/d.Vice versa,the amendment of Zn²⁺reduced the NRR to 0.28±0.02 kg N/m³/d,and Cu²⁺had no significant effect on the NRR(0.36±0.01 kg N/m³/d).From the analysis of microbial community,it was explained by the increasing abundance of anaerobic ammonium oxidizing bacteria(An AOB)only with Mn²⁺treatment,whereas predominantly promoted ammonium oxidizing bacteria(AOB)with Zn²⁺treatment.Additionally,the majority of Mn²⁺was identified inside An AOB cells,while Zn²⁺and Cu²⁺were mainly located in AOB.Our results indicated the synergistic effects of trace elements on nitritation-anammox,both short-term encouraging activities of An AOB and long-term altering microbial community.(2)In the long-term test of complex metalions,the optimal concentrations of Mn²⁺,Zn²⁺and Cu²⁺were 1.09,0.84 and 0.22 mg/L,respectively,and the NRR of CANON system increased by 23%.Under optimal conditions,the functional microorganisms of the CANON system are Candidatus Kuenenia and Nitrosomonas.The Pearson correlation coefficient showed that under the combined action of Mn²⁺,Zn²⁺and Cu²⁺,NRR was positively correlated with the activity and abundance of functional microorganisms.(3)The model calculated that the half-saturated concentrations of the three metalions of An AOB are Mn²⁺=1.09mg/L,Zn²⁺=0.84 mg/L,Cu²⁺=0.22 mg/L,and the short-term and long-term data reflect well.The practicality of the model is consistent,and the characteristics of ammonia nitrogen consumption and nitrous nitrogen accumulation are consistent,and the simulation and experimental data trends are consistent.It shows that the model based on matrix concentration suppression can well simulate the operation of SBR reactor under the influence of trace elements.The model can provide technical support for the addition of trace elements in the actual reactor operation.(4)The simultaneous nitrogen and SDZ removal in a lab-scale one-stage PN/A system was investigated.Results showed that maximum total nitrogen(TN)removal efficiency of 86.1%and SDZ removal efficiency of 95.1%could be achieved when treating 5 mg/L SDZ under DO conditions of 0.5?0.6 mg/L.Compared to anammox bacteria,ammonia-oxidizing bacteria(AOB)made a major contribution to SDZ degradation through their cometabolic pathway.A strong correlation between amo A gene and SDZ removal efficiency was found(p<0.01).In addition,the degradation products of SDZ did not exhibit any inhibitory effects on Escherichia coli.The findings suggest that it is promising to apply the PN/A process to simultaneously remove antibiotics and nitrogen from contaminated wastewater.