Removal Of Estrogen By SBR System Under Different C/N Influent Conditions

Steroid estrogen is one of the endocrine disruptors,which has the most potential risk of feminization.Although its concentration in water is only ng/L level,it can cause feminization of aquatic organisms and cause potential harm to human reproductive health.Therefore,as a new type of environmental pollutant,steroid estrogen has attracted wide attention of scholars from domestic to foreign.Sewage treatment plants are considered to be one of the important sources of estrogen in natural water.The effluent of sewage treatment plants results in estrogen levels ranging from several ng/L to tens of ng/L in the water environment.Therefore,improving the efficiency of estrogen removal in sewage treatment plants is an important measure to reduce estrogen entering the water environment.At present,activated sludge system is widely used in sewage treatment plants.It has been widely and deeply studied on the removal of organic matter,nitrogen,phosphorus and other nutrients,but the removal characteristics of estrogen have not yet been systematically studied.Estrogen can be degraded not only by the growth and metabolism of heterotrophic bacteria,but also by the co-metabolism of AOB.Therefore,the community structure of heterotrophic bacteria and AOB in activated sludge system largely determines the efficiency of estrogen removal.In the actual sewage treatment process,the C/N ratio of influent water will not only affect the removal of COD,N and P,but also affect the removal of estrogen by affecting the microbial community structure.The removal rates of COD and NH4+-N,NO2--N and NO3--N were measured by SBR system.Using Miseq high-throughput sequencing technology to analyze the microbial community structure in different activated sludge,and determine the population diversity,dominant bacteria and content of heterotrophic bacteria and AOB in activated sludge under different C/N ratio influent water conditions.After the SBR system was stable,E1,E2 and EE2 were added respectively,and the removal rates of three estrogens were determined by LC-MS.In addition,the activated sludge of SBR system was used to carry out static experiments,and the microorganisms in the sludge were inactivated by high temperature and high pressure sterilization,so as to clarify the capability of adsorption in removing different estrogens.The effect of AOB on the degradation of different estrogens was revealed by adding ATU to the activated sludge to inhibit the nitrification produced by AOB.The main results are as follows:(1)The removal rate of COD will increased with the increase of C/N ratio.When C/N ratio is greater than 5,the removal rate of COD can reach about 90%.The NH4+-N and NO2--N values of effluent increased with the increase of C/N ratio,this was because heterotrophic bacteria competed with nitrifying bacteria for dissolved oxygen and substrate.When C/N ratio was higher,heterotrophic bacteria were in obvious advantage.On the contrary,the NO3--N value of effluent decreased with the increase of C/N ratio.When the C/N ratio is low,the amount of NO3--N produced by nitrification is large,and the lack of carbon source will reduce the denitrification capacity and accumulate NO3--N.When C/N ratio is 2,the average of NO3--N in effluent reaches 41.10 mg/L.(2)The removal rates of E1 and E2 by SBR system under different C/N ratio influent conditions were higher,which could reach more than 95%.However,the average removal rate of EE2 was only 67.69%,which might be due to the cometabolism of AOB had weaker degradation ability to EE2,which made the removal efficiency of EE2 much lower than E1 and E2.(3)The richness of microorganisms in two SBR systems with C/N ratio 5 and 8 was higher than that in two extreme ratios of C/N 2 and 11,but the diversity of microorganisms in two SBR systems with C/N ratio 2 and 11 was higher than that in two SBR systems with C/N ratio 5 and 8,indicating that dominant microorganisms in two systems with C/N ratio 2 and 11 accounted for a larger proportion of total biomass.The nitrifying bacteria decreased with the increase of C/N ratio,and the number of heterotrophic bacteria increased significantly with the increase of C/N ratio.(4)The adsorption capacity of activated sludge to estrogen was EE2> E1 > E2.The adsorption capacity was related to Kow value and molecular structure of estrogen,and the adsorption effect at low temperature was better than that at high temperature.The adsorption isotherms of estrogens E1,E2 and EE2 at 10℃ and 20℃all conformed to Freundlich adsorption isotherms.The KF value of Freundlich adsorption constant decreased with the increase of temperature.the ?H of the three estrogens was less than 0,and these results indicated that the adsorption reaction was an exothermic reaction.The ?G of the three estrogens were between-20~0 k J/mol,indicating that the adsorption reactions were spontaneous and mainly based on physical adsorption.(5)The activity of heterotrophic bacteria in activated sludge could be effectively inhibited at 4℃.After adding ATU,the activity of nitrifying bacteria in activated sludge could also be inhibited.Compared with activated sludge without ATU,activated sludge with ATU reduced the removal rate of E1 by 15% and E2 by 18%,while the concentration of EE2 in water with ATU and without ATU didn’t change much.This indicated that the co-metabolism of AOB played an important role in the biodegradation of E1 and E2,but had little effect on the biodegradation of EE2.