Study On Culture Optimization And Bioaugmentation Of Photosynthetic Bacteria In Treatment Of Landfill Leachate

The complexity of the quality and quantity of landfill leachate lead to the difficulty and high cost of treatment,and also makes the treatment technology of landfill leachate has become a new reseatch hotspot in the field of envitonmental protection.Bioaugmentation technology has the advantages of strong pertinence,good treatment effect on target pollutants,simple operation and saving on investment and reconstruction cost,that could be used in the field of treatment of landfill leachate.The photosynthetic bacteria?PSB?have many metabolic pathways,the ability of removing pollutants and tolerance to substances,no excess sludge produce and no harm to the environment so that it has the advantage to be selected as bioaugmented strains,making it highly efficient and feasible to relize the improvement of activated sludge system onlandfill leachate with bioaugmentation.In this study,an activated sludge system was selected as the research ovject.A strain of photosynthetic bacteria with the ability to remove nitrogen and phosphorus was obtained after screening,and its optimised culture medium and conditions were oprimized,and then was added to the SBR system as a bioaugmentation strain.The effect of this strain on treatment of landfill leachate was investaged.The main conclusions are as follows:?1?A photosynthetic bacterium R.palustris was screened from landfill leachate after enrichment,separation,purification and culture.The charaterisitic absorption peak of the cell of the strain indicated that it contained carotenoids and bacteriochlorophyll-a.Morphological and molecular biology identification results determined it was Rhodopseudomonas palustris,which has the ability to remove organics,nitrogen and phosphorus under light-anaerobic and dark-aerobic conditions.?2?The medium and culture conditons of PSB R.palustris R1 were determined through single-factor experiments,orthogonal experiment and response surface methodology.The optimal media formula:NH₄Cl 0.5 g/L,sodium acetate 3 g/L,yeast extract 1 g/L,K₂HPO₄ 0.5 g/L,NaCl 0.1 g/L,MgSO₄ 1 g/L,CaCl₂ 0.05 g/L.The final optimized culture conditons were pH=7.5,T=33?,and inoculum concentration was 5%.The growth of the strain was larger than before and the maximum growth rate was 0.13h^-1 after cultured in the optimized medium.In addition,the PSB can effectively remove COD,NH₄⁺and TP,and in the process of removal of NH₄⁺,NO₂^-and NO₃^-were not generated and accumulated with pH rising.?3?The PSB was used to directly added into SBR reactor in forms of anaerobic?or anoxic?and aerobic alternately existed in the same zone to treat landfill leachate under different light conditions.The results showed that the removal rates of COD,NH₄⁺and TP in the experimental group with PSB added were 776.895%,65.964%and 94.036%under light-dark conditons,respectively.The results of experiment that combined with activated sludge system?SBR process?to treat landfill leachate by adding PSB showed that the average concentrations of effluent COD and TP in experimental group respectively were 229.022 mg/L and 1.508 mg/L,and the average concentration of NH₄⁺was reduced to 6.688 mg/L in the late test period of effluent.The addition of PSB can effectively and significant improve the effect of organics,nitrogen and phosphorus removal in activated sludge system,and availably reduce sludge production and cost.?4?Illumian Miseq high-throughput sequencing technology was applied to analyze the microbial community structure of activated sludge?S_c?added with PSB and activated sludge?S_b?without PSB.The results showed that the population abundance and biodiversity of the activated sludge system?S_c?with photosynthetic bacteria added were higher.The dominant phylums were Proteobacteria?42.76%?,Chloroflexi?18.25%?,Firmicutes?9.64%?,Acidobacteria?7.08%?,Bacteroidetes?6.02%?.The dominat genus were Rhodopseudomonas?11.56%?,Anaerolineaceae?4.28%?,Xanthomonadaceae?3.82%?,Blastocatellaceae?3.77%?.The activated sludge system showed better removal of organic matter,nitrogen and phosphorus under the action of the functional bacteria such as Rhodopseudomonas,Acinetobacter,Bdellovibrio,Exiguobacterium,Limnobacter,Planctomycetaceae,Terrimonas,Nitrosomonas,whose abundance in S_c were higer than S_b.The PSB as a bioaugmentation strain could not only stably exist in the activated sludge system,but also effectively improve its microbial community structure and performance in removing organics,nitrogen and phosphorus.