Study On The Degradation Of Low Concentration Phthalate Esters (PAEs) In The Tail Water From Municipal Sewage Plant

With the increasing water requirements, the discharge of domestic sewage is increasingconstantly. More and more organic pollutants are found in the tial water from municipalsewage plant, especially environmental endocrine disruptors, which are seriously harmful tohuaman health and environment. The conventional biological processes could not effctivelyremove these low concentration organic pollutants, therefore, to develop a new effectivetreatment processes is a necessary task. In this study, UV/H₂O₂and H₂O₂/O₃degradation ofthe low concentration PAEs was focused, with higher detection rate in the tail water frommunicipal sewage plant, leading the treated wastewater suitable for reuse. The concretestudies are showed as followings:（1） An analytical method for the determination of four phthalate esters in water has beendeveloped. The PAEs were extracted from water samples with an optimized soild-phaseextraction and quantification was achieved via GC/MS. It was found that the PAEs extractionrecoveries were over90%with the dichloromethane as extraction agent, anda sample flowrate of4mL/min.（2） H₂O₂oxidation or UV radiation separating process could hardly remove PAEs fromwater, while the UV/H₂O₂process is very promising for complete removal of PAEs inpolluted water. The degradation process also conforms to the pseudo-first kinetics equation.Higher degradation of PAEs was achieved in of H₂O₂dosage of3.0mM, and a UV irradiationintensity of24.26μw/m2, without adjusting initial pH value.The experimental results indicatethat H₂O₂should be added at an optimal concentration in order to achieve the best degrit wasnot necessary to adjust the initial pH value in the process because these is no obvious impactof PAEs degradation on different pH; The present of inorganic anions such as Cl-, CO₃^2-,NO_<sup>3-and H₂PO4-which are well known as radical scavengers would reduce the degradationof PAEs.（3） The H₂O₂/O₃process is a principlal advance oxidation process employed in watertreatment to enchance the removal of PAEs. The H₂O₂/O₃ratio and initial pH value are themain factors affecting the oxidation. This study results indicate that the90%removal rate wasachieved at the initial pH value of10, the H₂O₂/O₃ratio was2.0. The excess of H₂O₂or O₃ dosage can inhibit the degradation of PAEs in the process; the higher pH value could improvethe removal rate of PAEs; CO₃^2-and HCOO-could evidently inhibit the PAEs degradation,but NO_<sup>3-and H₂PO4-showed no obvious effect on the oxidation.（4） The degradation mechanism is actually the oxidation caused by·OH radicals, whichmainly attack the side-chain structure of PAEs, with the scission of C-C or C-O bond, PAEswere transformed to small molecule organics, and finally generate benzoic acid, reducing theenvironmental pollution and the harm to human health.