Study On Degradation And Mechanism Of Landfill Leachate

Landfill leachate is defined as the waste water generated from infiltration process of landfill which exhibits characteristics like high chemical oxygen demand(COD),high biochemical oxygen demand(BOD),high pollutant concentration,and high chroma.Moreover,various toxic and harmful substances contained in the leachate makes it difficult to be directly discharged.So far,the predominate treatment method of leachate,chemical flocculation,still showed inadequate effect as compared to the requirements of environmental protection standards.Therefore,it is of great significance to study the treatment methods of landfill leachate for environmental security.In this work,the origin,composition,pollution harm and the status of leachate have been systematically stated.The combination of three methods--pulse corona discharge method,three-dimensional electrode oxidation method,and biological degradation method was emphatically studied,and its feasibility and impact factors were evaluated.Besides,there are diverse types of organic pollutants in the landfill leachate,in which the typical substances such as phthalate,phenols and anilines contain benzene moiety and present extreme slow degradation rates.In this regard,we chose phenols as our representative to study the degradation mechanism of organic matter in landfill leachate.The main contents of this study are listed as follow:(1)Pretreatment research: impurities in the leachate were removed by centrifuge,and followed by coagulation,and the optimal conditions were determined to be 2g/L polyaluminium chloride(PAC).After the pretreatment,the COD of solution reduced from 6300 mg/L to 2500 mg/L,with total removal rate of COD reaching 60.32%;BOD reduced from 4000 mg/L to 1600 mg/L,showing total removal rate of 60%.(2)Experimental study of high voltage pulse discharge degradation: COD value after discharge treatment was measured by observing the discharge effect of electrode,and the result showed that 1.00 mmol/L Fe2+ in the solution gives optimal degradation effect.Experimental study on oxidative degradation of landfill leachate pretreated by high voltage pulse using corona technology gives the optimal processing conditions: pulse voltage 35 kV,discharge time 80 min,pulse width 45,the discharge frequency 55 Hz.At this condition,the treatment effect of pulse corona reached the highest,and the COD reduced from 6300 mg/L to 800 mg/L with total removal rate 87.30%;BOD reduced from 4000 mg/L to 982 mg/L with total removal rate of BOD reaching 75.45%.(3)Three dimensional(3D)electrode degradation experiment: the investigation of current intensity and capacities of different tar activated carbons reveals that at the highest processing capacity of 3D electrode,solution COD decreased from 6300 mg/L to 380 mg/L with total removal rate of COD reaching 93.97%,BOD reduced from 4000 mg/L to 266 mg/L with total removal rate of 93.35%.The optimal treatment condition is also obtained: current intensity 10 mA and 4.0 mm activated carbon selected as the electrode fill.(4)Biodegradation experiment: COD value of the solution after microbial treatment was measured by investigating the degradation effect of microbial treatment of landfill leachate.By analyzing the experimental data,the optimal conditions of biological treatment are: aeration amount 1/4,aeration time 8 h,microbial content 80 mL,and pH 7.The COD value decreases from 6300 mg/L to 245mg/L with total removal rate of 96.11%,BOD reduced from 4000 mg/L to 82 mg/L with total removal rate of BOD reaching 97.95%.(5)Theoretical research on the degradation of organic pollutants by ozone oxidation: the degradation mechanism of phenol in organic pollutants was studied on the level of 6-31+G(d,p)by using the DFT/B3 LYP method in Gaussian09 program,along with the degradation path of o-benzoquinone and p-benzoquinone.The study reveals that when the voltage and ozone concentration are not very high,the benzene ring has just been opened partially,and COD value of landfill leachate showed mild increase;but with the proceeding of discharge,if the voltage is further raised,COD value would decreased rapidly,and finally organic macromolecules degraded into small molecules.