Study On Migration And Transformation Of Representative Endocrine Disrupt Chemicals During Reclaimed Water Infiltrating Into Groundwater

As an unconventional source of water supply for river,reclaimed water can improve the ecological environment and effectively alleviate the problem of shortage of groundwater resources.However,trace pollutants in reclaimed water will naturally infiltrate into the ground along with reclaimed water,posing potential risks to groundwater security.In this study,four typical endocrine disruptors(EDCs)were researched,which were exogenous estrogen bisphenol A(BPA),natural steroid estrogen estradiol(E2),synthetic steroid estrogen ethinylestradiol(EE2)and glucocorticoid(Hydrocortisone,referred to as CRL).The study analyzed the process of EDCs migration transformation and regularities of spatial and temporal distribution during reclaimed water infiltration into groundwater,parsed the preponderant microbial community structure.Through the research of EDCs changes in reclaimed water supplied the groundwater in Chaobai River,it provided the technical support for reclaimed water to supply groundwater safely.In this study,adsorption and degradation experiments were carried out by the soil from Chaobai River to study the adsorption kinetics and adsorption thermodynamics of pollutants,and analyze the natural degradation kinetics characteristics of four EDCs and the influence of environmental factors on the degradation under static experimental conditions.The adsorption strength for CRL was the highest,followed by EE2 and E2,and the adsorption strength for BPA was the lowest.By the experiment of leached soil column,the transport and transformation properties and degradation characteristics of EDCs in soil medium were analyzed.The adsorption process conforms to the first-order kinetic model,and the Freundlich equation can well fit the adsorption thermodynamic process.The residual EDCs concentration in the effluent and soil of soil column in continuous recharge(CR)and wet and dry alternate recharge(WDAR)were relatively low,indicating that the main mechanism of EDCs removal was biodegradation,and soil column had the strongest adsorption and degradation effect on E2 and CRL.The process of attenuation in four kinds of typical endocrine disruptors were fitted with first-order dynamics model,and the attenuation coefficient were 0.068,0.052,0.047 and 0.046 m-1,respectively.By the comparison of the influence of two recharge mode on the transformation of EDCs,the result confirmed that WDAR had a better effect to control the migration to groundwater.Three aquifer medium in Chaobai River-loam(L),sandy loam(SL)and silt loam(SIL)were selected to analyze the metabolic pathway of glucocorticoid in different aquifer medium.The result confirmed that different aquifer medium had different effect in migration inhibition,which was associated with the physical and chemical properties of soil medium.When keeping 30 and 60 days of SIL column and SL column,EDCs concentrations presented a fast growth.There were two metabolism pathways of hydrocortisone,the one was initiated by the hydration of C-4 and C-5 double bonds on the A-ring,followed by A-ring cleavage,and the other one was composed of the side chain biodegradation and C-12 oxidation on the D-ring to form the ketone group,followed by D-ring carboxylation and cleavage.Leaching soil column could simulate the degradation characteristic of EDCs by advantage microbial communities in aquifer medium,and the dominant microorganisms were Sphingomonas,Pseudomonas,Methylotenera,Clostridia,Ardenticatenia and Anaerolineae,which play an important role in the degradation of EDCs.By the detection of EDCs concentration and microbial community in the reclaimed water recharged to Chaobai River,the EDCs content in groundwater presented obviously seasonal variation,and E2 and EE2 were not detected,but BPA showed the highest concentration in groundwater.BPA and E1 had a fast attenuation in the aquifer of 30 m,and E3 concentration had a higher accumulation and infiltrated into the underground of 80 m.When EDCs concentrations had a farther distance from the river center line,the lower concentration were detected.The distribution of EDCs concentration was affected by the hydraulic gradient of the aquifer,the adsorption capacity of the aquifer medium,the type of EDCs and the distribution of the microbial community.The dominant microorganisms in aquifer medium were Sphingomonas,Pseudomonas,Methylotenera,Methylobacter and Sphingobacterium.Microbial community structure was correlated with EDCs concentration,temperature,aquifer depth,TOC,pH and other factors.Temperature is the most important influencing factor affecting the microbial activity and intermediate metabolic function,thus influencing the intermediate degradation process of EDCs.