Advanced Treatment Of Leachate From Waste Incineration Plant By Activated Persulfate

Landfill leachate is a typical refractory organic wastewater, especially thebiochemical effluent. Reverse osmosistechnology is the main advanced treatmentprocess under the strict discharge standard. However, some problems of reverse osmosistechnology limited the application of memberane, so it is necessary to study theadvanced treatment of new technology.Sulfate radicals(·SO4) based-advanced oxidationproeesses have been developed in recent years and have been gaining inereasedattention for wastewater treatment. The advanced treatment of landfill leachatedescribed in this study provides three typical activation method—Fe0, heating, UVirradiation to stimulate persulfate (PS) to produce sulfate radical. These studies arefocused on the advanced treatment of landfill leachate of MBR effluent. The mainstudes are as followed:(1) Chemical oxygen demand（CODCr） is an important indicator to characterizethe content of organic pollutants in water,but the persulfate(S O2-28) in water wouldinterfere with the CODCrmeasurement results.In order to eliminate the interference, theCODCrvalues of different conclusionS O2-28in ultrapure water system is studied.Results showed thatS O2-28concentration was liner correlated with CODCr. The linearequations in low （0~150mg/L） and high concentration （0~1500mg/L） werey=36.1202x+0.5711（R2=0.9979, x—S O2-28g/L, y—CODCrmg/L） andy=45.1716x+38.0316（R2=0.9984）respectively, and the linear equations could beapplied to CODCrdetermination of standard COD solutions and environmental water.(2) The Fe0/PS system for the advanced treatment of landfill leachate was studiedthrough a series of batch experiments. The effects of oscillator’s speed（120-210r·min-1）, initial pH（pH0=3—8.1）,Fe0dosage（n（Fe）：n（PS）=0.5:1—4:1）andS O2-28dosage（m（PS）：m(12COD0)=0.5—2.0） on the oxidation efficiencies ofleachate were investigated on the condition of room temperature. The results showedthat,the removal rates of CODCrwas68%and the biodegradability index increased from0.07to0.35at the optimal conditions of oscillator’s speed=180r·min-1, pH0=7, PSdosage was m（PS）：m(12COD0)=1.25and Fe0dosage wasn（Fe）：n（PS）=1：1within6h. Furthermore, compared with Fe2+/S O2-28and Fenton treatment of the same batchleachate sample, the Fe0/S O2-28could achieve a higher CODCrremoval at an identicalchemical dose. For example, CODCrremoval were40%at m（PS）：m(12COD0)=1.25 during Fe2+/S O2-28treatmentand61%at m（H2O2）:m（2.125COD0）=1.25during Fentontreatment, but68%at m（PS）：m(12COD0)=1.25during Fe0/S2-2O8treatment.（3）In order to study the treatment efficienty of/PS system for landfill leachate,the temperrature (70—90℃),initial pH(pH0=3—8.1) andS O228dosage(m（PS）：m(12COD0)=0.5—2.0) were investigated. The results showed that when theS O2-28decomposed completely CODCrcan be reduced from800mg·L-1to below50mg·L-1andthe removal efficency reach95%and ammonia nitrogen and color are almost totallyremoved at the optimal conditions of70℃，pH0=5,S O2-28dosage is m（PS）：m(12COD0)=2.0.(4) In order to study the effect of UV actvated persulfate(S O2-28), firstly theperformance of UV//PS system was compared with UV/PS,UV/,/PS and UV//PSsystems, and then the effects of initial pH andS O2-28dosage on treatment efficiency inUV//PS system were investigated. The results showed that, the effectiveness ofUV//PS system is superior to other system. Under the conditons of pH0=4,S O2-28dosage is m（PS）：m(12COD0)=1.5in the UV//PS system within24h,CODCrcan bereduced from800mg·L-1to below100mg·L-1, the removal rate is about90%; TOCdecreased from334mg·L-1to20mg·L-1, the degree of mineralization is up to94%;ammonia nitrogen and color is almost completely removed.(5) In order to further study the removal of organic compounds in leachates byFe0/PS,/PS and UV//PS systems, three-dimensional fluorescence spectrum,synchronous fluorescence spectra and UV-Vis spectroscopy technique were used todetect the organic in water before and after treatment. The results of three-dimensionalexcitation-emission matrix (3D-EEM) fluorescence spectra showed Leachate of MBReffluent mainly containing visible area fulvic acid,ultraviolet fulvic acid and highlyexcited class tyrosine; Fe0/PS system can effectively remove visible area fulvic acid andultraviolet fulvic acid,but the efficiency of removing highly excited class tyrosine is nothigh;/PS and UV//PS systems can effectively remove all the above three kinds oforganics.The results of synchronous fluorescence spectra analysis showed the MBReffluent contains a large number of simple molecular structure and low degree ofcondensation organics and some large molecular weight complex organics; the Fe0/PSsystem can almost complexly remove the macromolecular organic matter and removemost of the small organic molecules of simple structure; the/PS and UV//PSsystems can remove almost all fluorescent substances of MBR effluent.The results ofUV-Vis spectra analysis showed that the absorbance of the organic matter in MBR effluent mainly in the ultraviolet region, namely organics with π-π*transition andconjugated system of the benzene ring structure; the Fe0/PS system can remove most oforganics with conjugated system of the benzene ring structure; the/PS and UV//PSsystems can remove almost all of the organic matter, except a very small part of theorganics with conjugated system of the benzene ring structure.