The Study Of Treating Leachate With Electro-chemical Method And Leachate Recirculation Method Combined Process

The quality of leachate wastewater changes obviously with theincreasing of landfill age. we must use suitable treatmenttechnology which has a stronger anti -pounds charge andadaptability .The organic matter density of leachate is high ,itsdensity scope variety is big ,making select a good treatmenttechnology harder. A single and the technique parameteradjustment inconvenient technology can't meet the requirementsfor treating leachate completely. Nowadays, lots of landfills'facilities for treating wastewater has exposed such problems moreor less. For this, treatment of leachate, not only considers thetreatment effects of technical method, but also even considers thismethod's adaptability to the variety of water quality and quantity.Physical and chemical methods, its condition can be controlledeasily the adjustment parameter is convenient and dependable, butbiological method has good adaptability to continuous variety ofleachate quality. Combining each method's characteristic,developing respective superiority ,the combination of physical andchemical method with biological method will be the main currentthought in future for treatment of leachate. So ,changes leachaequality condition of leachate in a short time ,improves thebiochemical treatbility of leachate , recuces the density do freeammonia , provides a better working condition for the succeedingbiological treatment, all of these seem to be more important .Forthis text, the combination of electro-chemical method withleachate recirculation method were applied for the treatment ofleachate and accelerating the stability of fresh waste, its feasibilitywas discussed. This thesis divides two parts proceed the research: the firstpart ,comprehensive consideration about the technique advantageof the electro -chemical method and different techniqueproblems in the aspect of pretreatment of leachate. According tothe investigative foundation of the domestic and internationalscholars on the study about deep treatment of leachate. Differentelectrode materials were investigated. Electro -coagulation ,Electro-chemical oxidation and Micro-electrolysiswere utilized in pretreatment of leachate, the best workingcondition was obtained respectively. Meanwhile, the feasibility ofeconomy and technique was proved by making a comparison ofdifferent electro-chemical pretreatment methods. The second part,on the base of conclusions draw from the first part electro-chemical experiments, combined with the current research inleachate recirculation ,the author put forward a new trial—thecombination electro-chemical method with leachate recirculationmethod were applied for the treatment of leachate and acceleratingthe stability of fresh waste. Experiment design point of departure:First, treat the old leachate which hasn't been treated in currentlandfills, to testify the feasibility of electro-chemical pretreatmentmethod in intensifying the treatment of leachate and acceleratingthe stability of MSW. Second, reduce the passive influence of theacid stage in the process of leachate recirculation in the fresh MSWbed, to testify the efficiency of the enhanced leachate recirculationmethod. Four Plexiglas pillar were build to simulate the leachaterecirculation process ,proceeding the analysis and comparison.Draw the following conclusions from the two part experiments:⑴ The Micro-electrolysis was not suitable for the actualapplication of leachate pretreatment before it wouldn't be furtherimproved. However , the two different electro-chemical methodsof electro-coagulation and electro-chemical oxidation wereeffective to pretreat high density leachate in a short time. The twomethods were not restricted by the variety of leachate quality andquantity, the electrode materials were simple and easy to get, theperiod of pretreatment was short ,leachate could be treated at anytime, the method had a good removal performance to someobstinate toxic pollutants , and the BOD5/COD ratio of leachatewas improved to a great extent, the biochemical treatbility of theleachate being pretreated was improved obviously ,all of thesewere of benefit to the succeeding biochemical.⑵ The optimum working condition of electro-coagulation andelectro-chemical oxidation was identified by experiment: when astudy of pretreatment of leachate by electro-coagulation methodwas carried out, using Fe anode and stainless steel cathode,electrode spacing was 1.5cm , current intensity was50mA/cm2 ,and electrolytic time was 90 minutes without addingelectrolyte, the removal rates of COD and NH4+ reached 57.6%and 40.1% respectively,the BOD5/COD ratio was improved from0.15 to 0.32;when a study of pretreatment of leachate by electro-chemical oxidation method was carried out, using Ti coated withRu and Ir anode and stainless steel cathode, electrode spacing was1.5cm , current intensity was 60mA/cm2 ,and electrolytic time was120 minutes without adding electrolyte, the removal rates of CODand NH4+ reached 48.6% and 53.6% respectively,the BOD5/CODratio was improved from 0.15 to 0.38. Meanwhile, the electro-chemical methods reduced the heavy metals density and thecoliform quantity of leachate, improved the succeeding workingcondition of biochemical process. By selecting anode and cathodereasonably ,the pretreatment time of leachate was accelerated, itseconomy and efficiency of treatment by comprehensiveconsideration were superior to traditional pretreatment method.⑶ When the old leachate being pretreated was recirculated to theexperiment pillar filled with old MSW, which had beendecomposed to a great degree, this method reduced the treatmentload of leachate, decreased the inhibition of high density heavymetals and ammonia ,and improved the biochemical treatbility,accelerated the reduction of COD density in the process of leachaterecirculation . With the experiment ,when PVN was 23.5 ,that is ,after 35 days from the beginning of leachate recirculation ,theCOD density of leachate by recirculation with pretreatment wasreduced to 218 mg/L ,and still remained a slight tendency ofdecline. Compared with the leachate recirculation withoutpreatment, the COD density was less than 300mg/L,attained thesecond grade standard of the GB/16889-1997 "Pollution ControlStandard for Life Garbage Landfill"in a short experiment time. If apattern was applied, leachate which was treated by electro-coagulation after recirculation ,its effect would be inferior to thepattern that leachate was treated by recirculation after electro-coagulation. Although the density of COD and NH4+ still reduced,the improvement of biochemical treatbility by electro -coagulation pretreatment for intensifying micro -organismaction was not found.⑷ For new garbage experiment bed,in the leachate recirculationdirectly system, although the moisture content of garbage landfillcan be increased in the early recirculation stage , it can't acceleratecomposition of the garbage, the micro-organism in the layer ofgarbage bed hydrolyze the organic pollutant of leachate mostly, theacidogenic bacterias grow and reproduce rapidly, the organic acidsof leachate accumulate, the value of pH decrease and theecological balance of micro-organism in the garbage layer wasdestroyed. Leachate after being pretreated by electro-coagulation,the value of pH was inclined alkaline (8.3) , the density of VFAwas 320 mg/L ,the density of COD decreased from 9008 mg/L to4021 mg/L ,then, the leachate was recirculated into experiment bedso as to decrease the inhibition of neutral micro-organismmethanogenesis caused by strong acidic condition of pH. It wasbeneficial for synthesizing the harmonious metabolism of micro-organism in the garbage layer, accelerated the stability of garbageand organic pollutants of leachate further degradation. The highdensity ammonia of leachate was one of important factors ,whichinfluenced the biological treatment also would inhibit the normalgrowth of micro-organism and the efficiency of treatment process.The leachate after being pretreated by electro -coagulationreduced the density of ammonia mostly ,from 1391.3 mg/L to430.1 mg/L ,this method provided a better living condition formicro-organism in the experiment bed.Electro-chemical method and leachate recirculation methodcombined process has a particular reference value in the area oftreating leachate and accelerating the stability of garbage ,remainsa further research.