Distribution And Removal Pathway Of Phthalic Acid Esters In Urban Sewage Treatment Plant

Endocrine Disrupting Chemicals(EDCs)are a class of highly toxic,highly accumulating organic pollutants with hormonal effects,which Entering the body will affect the normal endocrine system,leading to reproductive and immune dysfunction,and pose a great threat to human health and biological reproduction.Phthalates Acid esters(PAEs)are a kind of EDCs that are widely used in plastic products as plasticizers,which are easy to spread to the environment,resulting in phthalate pollution in the atmosphere,soil,water and other environmental media.Survey shows that phthalates pollution in our country's water environment is very serious,persistent PAEs were detected in various water.PAEs monitoring and removal has become an important subject in the field of wastewater treatment,which arouse the attention of environmental protection personnel at home and abroad.The effluent of urban sewage treatment plants is an important way for the PAEs to enter the water.The treatment process of a sewage plant can remove some of the PAEs from dirt and waste water and reduce pollution to the environment.Therefore,it is of great significance to study the distribution and removal of PAEs in municipal wastewater treatment plants and to search for the methods and technology for efficient removal of PAEs.In this paper,we chose four typical phthalate esters-dimethyl phthalate(DMP),diethyl phthalate(DEP),dibutyl phthalate(DBP)and Butylated benzyl phthalate(BBP)as the research object,and three sewage treatment plants in Xi'an were selected to carry out PAEs distribution and removal studies.The samples were collected from the effluent of each process section and excess sludge in three sewage plants,and analyzed with established pretreatment-High Performance Liquid Chromatography(HPLC)method,to obtain the removal rules and main removal routes of four kinds of PAEs in the sewage treatment plant.The main conclusions are as follows:(1)The optimum condition for analysis of PAEs were established based on high performance liquid chromatography: C18 chromatographic column(4.6*250mm,5um);Mobile phase,methanol-H2O(80:20,v/v);UV-Detector(238nm);Column temperature,ambient temperature;Sample size,20ul;Current speed,1ml/min.The average recoveries of four PAEs were between 84%~118.8% in water samples,and 88.8%~104.4% in mud samples.The relative standard deviation(RSD)ranged from 2.31%~4.26%.The method has high precision and good accuracy.(2)The concentration of PAEs in three sewage treatment plants in Xi'an was determined by high performance liquid chromatography.The total concentration of influent PAEs in the three sewage treatment plants in Xi'an reach to 66.10 ?g/L~120.77 ?g/L,which is higher than the level of the PAEs concentration in most areas of China reported in the literature.Among the four PAEs,DMP is of the highest concentration in the influent.The total concentration of effluent PAEs in the three sewage plants dropped to 6.29?g/L ~ 27.72?g/L,for PAEs contamination has been significantly reduced in sewage treatment plants,and the effluent DBP concentration can meet the emission limits of 0.1mg/L in the “Discharge standard of pollutants for municipal wastewater treatmentplant”(GB18918-2002).The total content of PAEs in the excess sludge of sewage treatment plant was between 10.81g/g ~26.02g/g,where the mass concentration of DBP was the highest,reaching to 5.25 ?g/g ~ 16.05 ?g/g.(3)The removal rule and removal effect of PAEs in the sewage plant were analyzed.The removal of PAEs from the WWTP mainly occurred in the primary settling tank,the A~2/O bio-pool,the anaerobic selection tank,the oxidation ditch,the fiber turntable filter and the secondary sedimentation tank.The A~2/O bio-pool mainly removed DMP and DEP,while the primary and secondary sedimentation tanks mainly removed DBP and BBP.The removal rate of PAEs in biochemical processing unit was the best,and the total removal rate was 63.81% ~ 73.63%.Secondly,the pretreatment unit and the depth treatment unit could remove 18.40% and 15.83% of PAEs in the two A~2/O process sewage plant.The total removal rate of PAEs was 68.72% and 70.79% respectively in the secondary treatment unit of A~2/O process and oxidation ditch process,and there was no significant difference in theremoval effect.The total removal rate of PAEs in three sewage treatment plants in Xi'an reached 68.57%~94.58%.(4)The main removal route of PAEs in the wastewater treatment plant was analyzed and the mass balance of PAEs total load in the sewage plant was established.PAEs are mainly removed by biodegradation and sludge adsorption in secondary treatment wastewater plants.Biodegradation is the main pathway for the removal of PAEs by A~2/O and oxidation ditch processes,but the rate of biodegradation of PAEs is very slow.The effect of sludge adsorption on PAEs was poor,and the PAEs adsorbed by the sludge were not converted into non-toxic and harmless substances.The three sewage treatment plants in Xi'an can reduce more than 60% of the water PAEs load.However,about 1.79% to 22.43% of the PAEs is only transferred from the sewage to the sludge and not completely eliminated from the environment,and the daily discharge of PAEs with effluent is still high,up to 31.42% of the influent load.