Research On The Occurrence And Transformation Of Steroid Estrogens In The Biochemical Treatment System Of Municipal Wastewater

As a typical endocrine disruptor,steroid estrogens are persisting in the environment and refractory to biodegradation.Steroid estrogens can cause the endocrine disturbance and feminization of even at the concentraion level of ng/L.Human and animal excretion and drug dosage are the major significant sources of environmental steroid estrogens.Which would enter the wastewater treatment plants?WWTPs?with the inlet of the industrial and domestic wastewater.Thus WWTPs have became a major source of steroid estrogens in the environment.However,WWTPs have limited capablilty to remove steroid estrogens and steriod estrogens remain in the effluent and the excess sludge would enter the environment with the discharge of effluent and excess sludge.These steriod estrogens would disturb the normal physiological and biochemical activities of the aquatic animals and further pose threat to human health through food chain and drinking water.Thus,researches on the occurrence and transformation mechanisms of steroid estrogens in the biological wastewater treatment systems have great theoretical and practical significance.In the present study,the occurence and removal of three typical steroid estrogens?E₁,E₂ and EE₂?in four full-scale WWTPs?the respective biological treatment processes are A/O,oxidation ditch,A²/O and A²/O-MBR?were investigated.Further,lab-scale static experients were performed to investigate the the migration and removal mechanisms of steroid estrogens.The results showed that the concentration range of steroid estrogens in the influent of WWTPs was ND-389 ng/L,while the concentration of EE₂ was the highest.The concentrations of steroid estrogens in the influent of WWTP employing A²/O process were higher than that of the other three WWTPs.It was observed that the removal of steroid estrogens mainly occurred in the secondary treatment units,and the contributions of aerobic stage and MBR compartment were higher than other units.And the sequence of steroid estrogen removal efficiency was E₂>E₁>EE₂.With the seasonal change,the removal effeciencies of steroid estrogens in WWTPs also varied with the alternation of seasons.The removal efficiencies of steroid estrogens was higher in the seasons with higher water temperature?22±3 ^oC?than that of the seasons with lower temperature?7±3 ^oC?.However,low temperature did not completely inhibit the removal of steroid estrogens.Since the investigated WWTPSs have different design and operation parameters,geographical locations,influent characteristics and other related factors,the removal efficiency of steroid estrogens was also different.The removal efficiencies of steroid estrogens in the oxidation ditch processwas higher than other WWTPs.The removal rates of E1,E2 and E3 were 82.93%,100%and EE2 87.32%,respectively.The removal of steroid estrogens in WWTPs was mainly accomplished by adsorption and biodegradation.Among them,biodegradation was dominant and aerobic biodegradation was better than anaerobic biodegradation.The aerobic biodegradation efficiency was 40-55%,whole the anaerobic biodegradation efficiency was only 31-45%.The removal efficiency of E2 was the best,while the anaerobic and aerobic biodegradation efficiencies were 45%and 55%,respectively.The adsorption rate of steroid estrogens by sludge was fast in the first four hours,and after 16 hours,the adsorption equilibrium was basically achieved.The adsorption capacities of sludge stemed from differnt sources following the sequece showed below:aerobic sludge>sludge from MBR>anaerobic sludge.It was found that the diversity of microbial community in aerobic stage and MBR pool was higher than that in anaerobic stage and anoxic stage by analyzing the microbial community structure of activated sludge.And the biodegradation of steroid estrogen is closely related to the denitrification process.In the present study,the occurence and removal mechanisms of steroid estrogens in four different WWTPs was investigated.The results accomplished in this study will promote the investigations on the removal mechanisms of steriod estrogens in differnt biological wastewater treatment processes and environmental factors and operational parameters closely related with the activated sludge adsorption and biodegradation to steriod estrogens,which have great theoretical and practial significane to enhance purification efficiency of the present WWTPs to the emerging organic pollutants like steriod estrogens and the development of innovative processes and technologies.