Research Of The Microbial Community Dynamics On Landfill Leachate Treatment By Biofilter

The sanitary landfill disposal is the most economical techniques of municipal refuse treatment at home and abroad. However, the landfill leachate produced from the landfill may cause serious pollution to groundwater, surfacewater and its surrounding. The landfill leachate has complex composition and is difficult to deal with. It is a significant and urgent task to find a proper technology on leachate treatment.In this paper, biofilter reactors (A, B, C and D) were built to study the removal efficiency of landfill leachate. Aged refuse from Shanghai Laogang Landfill and porous waste at different ratio of 2:1,1:0,1:2 and 0:1 were packed as carrier. The biofilters were operated at different temperature (40℃,30℃,20℃,10℃and 5℃) and hydraulic loading. The pollutants remove efficiency of each reactor, its microbial community structure of biofilters-as well as the relationship of functions at different stages were studied.The main conclusions were drawn as followings:(1)The NH3-N removal was above 90% at higher temperature, the NH3-N in effluent of A and B mainly packed with aged refuse began to rise and the removal efficiency decreased by 45% when the temperature reduced to 20℃, while the NH3-N in effluent of C and D mainly packed with porous waste increased until the temperature decreased to 10℃, and removal efficiency decreased by 15%; reactors had different TN removal efficiency, B had the highest efficiency of up to 53%, while the efficiency of D had less than 15%. Reactors had different tolerance to lower temperature, the temperature had a siginificant influence on D when it decreased to 10℃, the COD removal efficiency dropped by about 20%, while a little impact on A, the COD removal declined only 6%. The removal efficiency of reactors had a great relationship with the temperature.The COD in effluent of B and D increased significantly because of the addition of bacteria, increased about 26% and 40% respectively, which indicated that the bacteria addition enhanced the function of reactors.(2)The initial diversity of bacteria and AOB (Ammonia Oxidizing Bacteria) in aged refuse were very low. The microbial diversity increased and the microbial community structure changed complex as the biofilters operation, which indicated that the microbes become acclimated to the leachate treatment.(3)The carrier had significant influence on the microbial community structure of reactors.The result of cluster analysis in each bioreactor was different, which indicated that carrier was the most crucial factor on the microbial community structure and different structure led to different functions. Due to the stronger permeability of porous waste in D and better anaerobic condition in B, D had better nitrification but weaker denitrification than B. The microbial community structure in upper, middle and lower parts of B showed that most of AOB existed in the upper and middle regions, it indicated that nitrosification may occur in this area.(4)The temprature had effects on the microbial community structure in reactors as follows:The bacteria community structure similarity between 40℃and 30℃in reactor A was low, which indicated the dramatic changes. When the temprature reduced to 20℃and 10℃, the structure similarity increased and became more stable, reactor A had stronger weaker temperature resistance. B had the same rule. Reactor C and D, kept a similar community structure between 30℃and 20℃, and had a great difference when the temperature dropped to 10℃. It shows that the effect of temperature on microbial community in porous waste bioreactor was more considerable than that in the aged refuse bioreactor. The diversity index of AOB in reactor A, C and D was higher than reactor B, the change of structure in reactor B wasn't obvious because of the poorer permeability of aged refuse.At lower temperature, the addition of bacteria strengthened the organic removal, the community structure analysis showed that the bacteria addition changed the formerly community of reactors and enhanced the operational function of the system.(5)The major microbal colonies in the filters were Proteobacteria and Actinobacteria, most of the dominant species were Corynebacteriaceae and Enterobacteriaceae, such as Corynebacterium, Shigella and Proteus; dominant AOB belonged to Proteobacteria, the main species were Nitrosomonas.The distribution of these microbes is corresponding to reactors'functions. For example, Comamonas sp., related to aromatic compounds biodegradation, nitrification and denitrification, appeared in the upper area; Desulfovibrio sp., anaerobic SRB, had a direct relationship with organic pollutants and heavy metal biodegradation, appeared in the lower area; Corynebacterium sp. BBDP21,uncultured gamma proteobacterium,Corynebacterium sp.'Mali 24',uncultured proteobacterium clone F27₂E_FL mainly presented in the lower temperature enhanced D, and they also appeared frequently in the reactors which had good performance, these indicated that they may be high solution bacteria in the system.