Effect of Hg on nitrogen removal performance of wastewater treatment system in low-pressure conditions
The presence of mercury(Hg)in wastewater treatment systems in low-pressure areas can potentially reduce the efficiency of wastewater treatment.In a laboratory-scale study using a sequencing batch reactor(SBR),the impact of Hg under low-pressure conditions on wastewater treatment systems was investigated.It was found that Hg significantly lowered the removal rate of ammonia nitrogen(NH4+-N),particularly at high concentrations.The removal rate of NH4+-N decreased from 89.73%to 38.71%with increased Hg concentrations.Hg had a detrimental effect on the nitrogen transformation process within the SBR cycle.At an influent Hg concentration of 250 μg/L,the specific ammonium oxidation rate(SAOR)and the nitrite reduction rate(SNIR)decreased by 96.74%and 96.91%,respectively,and the activities of related functional enzymes decreased by 100.00%and 97.87%,respectively.Furthermore,Hg altered the morphology and structure of the activated sludge,leading to the disintegration of the overall sludge structure and changes in surface characteristics.It also inhibited the production of extracellular polymeric substances(EPS),particularly affecting the protein content.In terms of the microbial community,the addition of Hg significantly altered the structure of the activated sludge community,especially affecting functional genera related to the nitrification process,such as Nitrosomonas and Nitrospira.Therefore,attention needs to be paid to the impact of the presence of Hg in the sewage treatment system under low-pressure conditions.
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