| Incineration leachate is a typical high-concentration organic wastewater.The anaerobic methanogenic biological treatment process is generally used to remove most of the organic matter and recover energy in the leachate.However,the incineration leachate has extremely high COD concentration(～55,000 mg/L),and high salinity,high ammonia nitrogen,aquatic humic substance(AHS)and other components that inhibit the biological activity,affecting the syntrophic oxidation organic matte for methanogenesis in anaerobic system,leads to the accumulation of volatile fatty acids(VFAs)and decrease of pH,which in turn affects the anaerobic treatment efficiency and the methane production.Direct interspecies electron transport(DIET)is considered to be a more efficient electron transport pathway in anaerobic systems because it does not require an interspecies electron carrier.Conductive materials can promote DIET between microorganism.However,the reinforcing effect and mechanism of conductive materials for incineration leachate containing high concentrations of complex organic matter and VFAs are still unclear.Therefore,this paper explores the enhancement effect of conductive materials on anaerobic biological treatment in various extreme environments,and reveals that the strengthening mechanism on anaerobic reactor treating incineration leachate via conductive materials.In this paper,the effects of combined inhibitors on anaerobic methanogenesis were studied by anaerobic methanogenic batch tests.The results of the range analysis showed that the combined inhibitor concentration showed the greatest inhibitory effect on the methanogenic activity and organic matter removal of the sludge when the calcium ion was 6000 mg/L,the ammonia nitrogen was 400 m/L and the AHS was 4000 mg/L.Moreover,it is determined by variance analysis that the change of calcium ion concentration has the most significant effect on anaerobic methanogenesis.The concentration of different propionate and butyrate remaining in the anaerobic system is mainly due to the combination of inhibitory factors inhibiting the active genes of propionate degrading bacteria and butyrate degrading bacteria in anaerobic systems,as well as the growth of methanogens,which resulted in the hindering of the methanogenesis of syntrophic oxidation propionate and butyrate,and showed a more obvious inhibitory effect on propionate.In view of the accumulation of VFAs caused by high organic matter concentration and combined inhibitor concentration n incineration leachate,the treatment efficiency was studied by adding nano-magnetite in the anaerobic reactor.The results show that the nano-magnetite reactor has a higher COD removal rate(89.0%)and methane production rate(4.8 m3STP/(m3·d))than the control reactor at organic loading rate(OLR)of 18.2 kgCOD/(m3·d).The concentrations of acetate(13.5 mM)and propionate(8.5 mM)in effluent were significantly lower than control reactor,mainly due to the presence of nano-magnetite conductive materials to promote syntrophic oxidation metabolism of VFAs in anaerobic systems,alleviating the accumulation of VFAs(especially propionate).The abundance of the Anaerolinaceae with extracellular electron transport in magnetite reactor is twice as high as that in the control reactor,which can metabolize organic matter for electrons generation.The electrons are transferred to methanogens(Methanosarcina and Methanosaeta)to reduce COZ for methane production via nano-magneite conductive material.In order to solve the problem that the nano-magnetite adsorbed on the surface of the microorganism is lost with the sludge,the strengthening effect is not obvious under the condition of high OLR.In this paper,the carbon cloth conductive material can be used as permanent conductive conduit to strengthen the high OLR impact ability of the anaerobic system.The results show that the presence of carbon cloth conductive material can increase the maximum OLR by 34%that the anaerobic system can withstand to OLR of 49.4 kgCOD/(m,d),the COD removal rate was 80.1%,and the methane production rate was 15.3 L(STP)/d.A variety of bacteria with extracellular electron transport(Syntrophomonas,Streptococcus and Bacteroides,total relative abundance of 30%)and methanogens(Methanosarcina and Methanospirillum,total relative abundance 50%)that can accept electrons for methane production are enriched on the carbon cloth,and the total abundances of them in carbon cloth reactor are twice and 5 times that of the control reactor,respectively,indicating that the two organisms can use the carbon cloth conductive material as a conductor for DIET.The increased sludge conductivity in the carbon cloth reactor was twice that of the control reactor,which may be due to the increase in the conductive pill e-pili involved in DIET in the sludge of the carbon cloth reactor.It is further proved that microorganisms in anaerobic systems may conduct electron transfer through DIET.In this study,granular activated carbon(GAC)with high specific surface area and electrical conductivity was incorporated into a bioreactor fed raw incineration leachate.The results showed that the non-amended control reactor soured immediately and collapsed within 17 days.When HRT of the GAC-amended reactor was stepwise decreased to increase OLR to 25.0 kgCOD/(m3·d),COD removal efficiencies remained stable at>90%.A further increase to 36.7 kgCOD/(m3·d)caused COD removal efficiencies to drop slightly to～83%but the VFA/alkalinity ratio remained below 0.4 indicating that the system continued to operate stably and without risk of acidification.Metagenomic analysis of the GAC-amended reactor revealed that Geobacter and Methanosarcina species known to participate in DIET,became more abundant over time.In addition,the abundance of genes coding for proteins thought to be involved in DIET such as electrically conductive E-pili and the outer membrane c-type cytochrome,OmcS,increased significantly.This indicates that the presence of GAC effectively establish DIET between Geobacter and Methanosarcina species in anaerobic systems. |
PDF Full Text Request