Study On The Effect And Mechanism Of Perfluorooctanoic Acid On Sewage Nitrogen And Phosphorus Removal And Sludge Anaerobic Digestion

In recent years,perfluorooctanoic acid（PFOA）,the main ingredient in the manufacture of non-stick coating Teflon,has caused widespread concern about the potential harm to human health.The mass production and use of PFOA lead to its residual components inevitably entering the sewage treatment plant,but its impact on sewage and sludge treatment and its mechanism are still unclear,which will cause important hidden dangers to the operation of the sewage treatment plant.In this paper,the effects of different concentrations of PFOA（0.5,5 and 20 mg/L）on biological nitrogen and phosphorus removal and nitrous oxide（N₂O）emissions from sewage have been studied through long-term continuous experiments.The effect of PFOA（10,20,50,100 and 200 mg/kg TSS）on sludge anaerobic digestion and its mechanism was explored through batch experiments and long-term semi-continuous experiments.The results show that PFOA has no obvious effect on the performance of biological phosphorus removal,but it will significantly improve the performance of nitrogen removal and reduce N₂O emissions.The existence of 20 mg/L of PFOA increased total nitrogen removal efficiency from 78.7±6.89%to 86.8±6.39%and reduced N₂O emission factor from 6.02±0.24%to 4.43±0.10%.PFOA stimulates the release of extracellular polymer（EPS）from microorganisms,and combines with EPS to produce PFOA-EPS conjugate,which affects the mass transfer rate,thereby intensifying the electronic competition of oxidoreductase,thereby reducing the rate of nitrification.In addition,PFOA reduces the activity of phosphorous accumulating bacteria and glycogen accumulating organisms,saves carbon sources for denitrification,promotes the activity of reductase,makes denitrification more thorough,and reduces the production of N₂O.Further research found that PFOA significantly inhibited the methane production of sludge anaerobic digestion.In the presence of 200 mg/kg TSS PFOA,the cumulative methane production decreased from 197.1±1.92 to 159.9±3.10 m L CH₄/g VS,a decrease of 18.8±0.37%.PFOA stimulates anaerobic microorganisms to produce a large amount of EPS（mainly protein）and combine with it,which not only hinders the dissolution of sludge organic matter,but also increases mass transfer resistance and occupies enzyme active sites,thereby inhibiting key enzyme activity and acidification and methanation processes.PFOA can also induce the production of reactive oxygen species,which not only triggers oxidative stress and protease synthesis obstacles,but also directly leads to cell inactivation.In addition,PFOA reduces the diversity of microorganisms,especially the abundance of acid-producing microorganisms and hydrotrophic methanogens,making the microbial community unfavorable for acidification and methane production.This study explores the effect and mechanism of PFOA on the performance of biological nitrogen and phosphorus removal from sewage and anaerobic digestion of sludge,reveals the influence behavior and mechanism of PFOA in sewage treatment,and provides new insights into the environmental behavior of PFOA.This research provides new insights into the environmental behavior of PFOA,and has important theoretical and practical reference significance for ensuring the normal operation of sewage treatment plants.