Study On Performance And Microbial Community Succession Of Partial Denitrification System Under The Effect Of Typical Perfluorinated Compounds

Perfluorooctane sulfonic acid(PFOS)and perfluorooctanoic acid(PFOA)are representative compounds of many perfluorinated compounds(PFCs).Due to their low surface tension and high surface activity,PFOS and PFOA are widely used in industrial production and commercial consumption,such as fire extinguishing agents,firefighting foams and surfactants,etc.The mass production and use of PFOS and PFOA make Industrial wastewater containing large amounts of PFOS and PFOA enter municipal wastewater treatment plants.Traditional primary treatment in wastewater plants has no effect on the removal of PFOS and PFOA.Even after the secondary microbial treatment in wastewater treatment plants,the concentration of PFOS and PFOA in the effluent are increased even more due to the microbial degradation of the precursors of PFOS and PFOA.As partial denitrification(PD)can produce NO₂^--N stably,the bacterial activity are not easily affected by environmental factors such as temperature and p H,solving the problem that the anaerobic ammonia oxidation process(Anammox)is limited by the continuous supply of NO₂^--N,guaranteeing the feasibility and stability of the anaerobic ammonia oxidation process^[1].The partial denitrification coupled with anaerobic ammonia oxidation technology has the advantages of low energy consumption,low sludge yield and low greenhouse gas emissions,and has become a new research direction for wastewater denitrification.In this study,the effect of different PFOS and PFOA concentrations on the performance and microbial community succession of short-course denitrification system was investigated with perfluorinated compounds in NO₃^--N containing wastewater.The main experimental results were as follows:(1)PFOS and PFOA had no inhibitory effect on the nitrate reduction rate(NRR)of the PD system in the short-term tests and remained at high levels at all concentrations.The nitrite accumulation rate(NAR)was affected by PFOS and PFOA and tended to decrease,but the NAR still reached more than 80%.At high concentrations,PFOS and PFOA could have a serious impact on the nitrite production rate(NPR).When the highest concentrations of PFOS and PFOA were applied,the NPR of the system was only 55.59%and 50.18%of the maximum NPR without PFOS.(2)In the tests on the long-term effects of PFOS on the PD system,there was no significant inhibition of short-course denitrification sludge metabolic activity by PFOS.The content of polysaccharides and proteins in the sludge extracellular polymer(EPS)did not show a significant increase in the test.The results of this study showed that there was no significant increase in polysaccharide and protein content in the sludge extracellular polymer(EPS).The microbial community structure of the sludge systems affected by PFOS at various concentrations was analyzed by high-throughput sequencing techniques.The denitrifying,high NO₂^--N accumulating genus Thauera was the dominant genus throughout the long-term experiment.The relative abundance of Denitratisoma spp.with denitrification increased with increasing PFOS concentration.(3)Although PFOA did not significantly inhibit the metabolic activity of the partial denitrification fouling in the long-term effects of PFOA on the Although PFOA did not significantly inhibit the metabolic activity of the partial denitrification fouling in the long-term effects of PFOA on the short-course denitrification system.However,under the stimulation of PFOA,the microorganisms appeared to secrete excessive EPS,and their polysaccharides and proteins increased from 15.95 and 43.36 mg/g VSS at the beginning of the test up to 35.03 and 96.83 mg/g VSS.The sludge concentration decreased from 3339mg/L MLSS at the time of PFOA dosing to 1830 mg/L at the end of the trial,but Thauera spp.remained the dominant genus throughout the long-term trial.The above results show that the PD system has a high NO₂^--N accumulation rate in the presence of high PFOS and PFOA concentrations,which provides theoretical data to support the PD process for treating actual PFCs contaminated wastewater.