The Fate Of Phthalates In Landfill Leachate Treatment Systems

Phthalate esters?PAEs?are the most widely used plasticizers in the plastic industry.They can enter the food chain through biological enrichment of animals and plants,then affect human reproduction,development and behavior.They have become a global organic pollutant of environmental hormones and attracted great attention from various countries.Landfill is the main method of waste disposal in China.Waste plastics are usually treated together with other domestic waste,accounting for about 10¹5%of the total amount of waste.Most PAEs can not be degraded naturally in the landfill process,and will eventually be discharged with leachate,which may cause potential hazards to the surrounding environment such as soil,surface water and groundwater,and ultimately threaten human health.In this thesis,the removal rate of PAEs in AAO treatment process was studied.On this basis,the concentration of PAEs in sewage and sludge phases in each reactor was detected.And the transformation of PAEs was also analyzed.The main conclusions are as follows:?1?Sampling schemes of sewage and sludge were determined,and the analytic technique of two kinds of PAEs?DBP and DEHP?in leachate was optimized.The standard recovery rates of DBP and DEHP in sewage phase were 66.1⁷4.4%and 90.6⁹5.9%respectively,and those of DBP and DEHP in sludge phase were 73.6⁹7.6%and 98.8¹06.7%respectively.?2?Pre-experiment was carried out in beakers.Domestic sewage and leachate were treated with sludge of different concentration from a chemical plant.The conventional indexes of water quality were determined.It was concluded that the sludge concentration range of8¹1g·L^-1 was the best for the treatment of the two kinds of sewage.Sludge was cultured with domestic sewage and leachate of different proportions.Routine indexes of water quality were determined to caculate the maximum leachate concentration and domestication scheme that the sludge could withstand.?3?The COD degradation efficiency under different ratios of aged leachate and domestic sewage was tested and compared.50%leachate with 50%domestic sewage was selected as the influent when the reactor started.When the reactor was stable,the removal rates of COD and BOD₅were 55.78%and 62.46%respectively.This indicated that the reactor had limited effect on organic matter removal in aged leachate.?4?The removal rate of DBP was more than 94%,while that of DEHP was about 75⁷8%.DEHP was more difficult to remove than DBP.The results of mass balance calculation showed that about 33.7⁵0.7%of DBP was degraded by microorganisms,1.2⁹.3%residual in wastewater and 47.7⁵5.6%adsorbed in sludge,0.4¹.4%was contained in the final effluent,while about 15.0¹9.0%of DEHP was degraded by microorganisms,14.4¹4.5%residual in wastewater,61.4⁶4.5%adsorption in sludge,5.2⁶.0%was contained in the final effluent.Therefore,the main mechanism of DBP removal in leachate was biodegradation and activated sludge adsorption,while the main mechanism of DEHP removal in leachate was activated sludge adsorption.Two mechanisms of PAEs removal may be related to their molecular structure:hydrophobic DEHP is more difficult to degrade than hydrophilic DBP.PAEs were not completely removed when they were adsorbed into sludge.Therefore,how to reduce the adsorption capacity of PAEs and improve the biodegradation efficiency of leachate treatment process needs further study.