Enhancing Anaerobic Treatment Of Fresh Incineration Leachate Using Functional Strains And Microbial Electrolysis Cells

Fresh leachate generated from municipal solid waste(MSW)incineration plants is a kind of typical organic wastewater with extremely high chemical oxygen demand(COD)and biochemical oxygen demand(BOD)concentrations.Anaerobic biomethanogenic treatment was usually adopted as an effective method to remove the organic matters in fresh incineration leachate,however,treatment efficiency of anaerobic biomethanogenic reactor was limited by the complex components in incineration leachate.Traditional anaerobic biomethanogenic treatment is impeded by high organic loading rates and long rentention times.In addition,concentration of volatile fatty acids in the effluent of anaerobic treatment is still high and there is possibility for further utilized.And furthermore,the degradation of some refractory organics(e.g.humic substances)in the incineration leachate is not efficient and their relatively high redox potentials cause them to compete with methanogens for electrons,which can reduce methane recovery.Therefore,it is very important to explorer more effective methods to stimulate the incineration leachate treatment processes.In this study,functional stains enhancement and microbial electrolysis cells(MEC)adopted to solve these problem.Three functional strains with salt tolerance and COD degradation ability were screened to treat fresh incineration leachate.The growth conditions(temperature,pH and inocula)of these three strains were investigated and the 16S rDNA information was documented by static tests.The optimum temperature of S1,S2 and S3 were 35℃,35℃and 25℃,respectively;the optimum pH for S1,S2 and S3 were 6,6 and 8;the proper inoculum dose for them was 10%.Species construction was also conducted to enhancing COD removal,and when the bacteria consortium of Strain 1 and Strain2 with the noculation ratio of 1:2 and influent leachate COD at 20,000 mg/L,the COD removal effiency reached as high as 54.3%,33.2%higher than that of anaerobic sludge.COD removal rate and methane production of UASB were both increased by bacteria consortium addition,and organics with high molecular weight were also enhanced by 15%.MEC was incorporated into sequencing batch anaerobic reactors for fresh incineration leachate treatment.COD removal efficiency and methane production was improved by 8.7%and 44.3%by MEC compared to the control reactors,reapectively.And the degradation rate of large macromolecules was substantially higher(96%vs 81%)in MEC than control effluent,suggesting that MECs stimulated degradation of refractory organic matter and reduced humification.Exoelectrogenic bacteria(Desulfuromondales and Geobacter)and methanogens(Methanosarcina and Methanospirillum)known to form syntrophic partnerships were enriched by MEC.The experimental results show that MEC were more effective at treatment of MSW incineration leachate,and should be taken into consideration when designing future treatment facilities.However,the OLR of reactor combined with MEC was still not promoted significantly,which was probably because of the small superficial area of electrodes of MEC.Electrodes of carbon materials with different specific surface were used to investigate the effect of material on the performance of anaerobic treatment.Carbon fiber was proved to be more appropriate as electrode thancarbon cloth and car-bon bar.Compared to MEC with carbon cloth or carbon bar electrode when influent COD was 32,000 mg/L,COD removal rate in MEC with carbon fiber electrode was 8.3%and 43.1%higher,respectively;the ratio of organics with high molecular weight in effluent was reduced by 4.3%and 12.7%;methane production was promoted by 48 mmol/d and 161 mmol/d with methane conversion rate increasing 4.1%and 17.0%,respectively.When the influent COD increased to 40,000 mg/L,COD removal rate and methane production were 48%and 248 mmol/d,higher than other reactors.The experimental results demonstrate that larer specific surface could enhance the performance of MEC.Bacteria consortium enhancement and MEC were both used in anaerobic reactors and the treatment efficiency of fresh leachate from MSW incineration plants was further improved:COD removal rate was improve by 8%and 3%,and methane production was increased by 37%(130 mmol/d)and 15%(49 mmol/d)compared to reactor enhanced by bacteria consortium or MEC,respectively.Metabolism of volatile fatty acids was accelerated and the time achieved steady operation was shorten.