| Landfill leachate, generating during the process of sanitary landfill of municipal solid waste, is complex in composition and featuring high concentration of ammonia and low C/N rate, which is hard to be treated by the traditional physical and biochemical wastewater treatment method. Aged-refuse bioreactor is a low cost and stable running technology, which can remove contaminants with aged refuse as medium by microbial degradation and adsorption function. The nitrogen removal functional microbes such as ammonia oxidizing bacteria (AOB), denitrifying bacteria in aged refuse play an important role in nitrogen removal system. Since the microbial community structure in reactor will change with the operating conditions, and affect the nitrogen removal efficiency, the study of nitrogen removal microorganisms will be helpful to understand the microbial structure and its denitrogen mechanism, and therefore provide a theoretical basis for optimizing the operation of the reactor.The biological nitrogen removal process of both laboratory aged-refuse bioreactor and Laogang municipal landfill on-site aged-refuse bioreactor treating landfill leachate were investigated. The microbial community structures of AOB, denitrifying bacteria and anaerobic ammonia oxidation bacteria (Anammox) in laboratory bioreactor at different operating temperatures (20℃and28℃) were analyzed by molecular technologies of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative real-time polymerase chain reaction(qPCR), the functional microbial community structure of on-site bioreactors at different months (July and August) were analyzed as well. Meanwhile, the nitrogen removal performance of the two bioreactors were studied, and the relationship between the microorganisms in the bioreactor and the nitrogen removal efficiency was further explored from the view of microbial ecology.Conclusions in this paper were drawn as follows:(1) With respect to the laboratory aged-refuse bioreactor, removal rate of total nitrogen and ammonia nitrogen were45%and29%when the bioreactor operating at28℃, which are higher than that at20℃. The result of molecular detection indicated that there existed AOB、nirS and Anammox at two operating conditions(20℃and28℃). However, PCR-DGGE results showed that the change of the operating temperature affected the microbial community structure in the bioreactor. qPCR results showed that the number of total bacteria in the aged-refuse bioreactor operating at28℃was7.50×106Copies per gram soils(Copies/g),2.3times of that at20℃. The number of Anammox bacteria at20℃and28℃were4.70×103Copies/g and4.17×103Copies/g, respectively.(2) As for on-site horizontal-type and tower-type aged-refuse bioreactors in Laogang in July and August2012, total nitrogen removal rate were both about80%, while COD remove were only about60%. Molecular detection showed that there existed anammox functional genes in both horizontal-type bioreactor and tower-type bioreactor.(3) There were obvious differences in the community structure of total bacteria, AOB and denitrifying bacteria between horizontal-type and tower-type aged-refuse bioreactors in summer, but the dominant species of nitrifying and denitrifying bacteria were the most same, they had high similarity with bacteria which mainly exist in sewage treatment system. The little difference in bacterial community structure at different depths (0.2m,0.5m andlm) of the horizontal-type bioreactor showed that the microbial community structure of each bed was relatively stable.(4) The number of total bacteria in Laogang on-site aged-refuse bioreactors was at a level of106～107Copies/g, and those of AOB, denitrifying bacteria and Anammox bacteria were basically at a level of103-105Copies/g. The proportion of AOB in total bacteria was higher than those of the denitrifying bacteria and Anammox bacteria, both of which accounted less than1%of total bacteria. The value even decreased as the processing stages increased, which showed that denitrification mainly happened in the first stage and weakened step by step, this result corresponded with the nitrogen removal efficiency of each bioreactor. The number of AOB and denitrifying bacteria in tower-type bioreactor was higher than those in horizontal-type bioreactor, showed that the tower-type bioreactor had stronger nitrification-denitrification reaction, agreeing that the COD removal efficiency in tower-type bioreactor was better than the latter.This study showed that temperature change of aged-refuse bioreactor affected the nitrogen removal performance of landfill leachate. In on-site aged-refuse bioreactors, the proportion of AOB in total bacteria was higher man other functional bacteria, and the nitrogen removal process mainly happened in the first stage, and weakened step by step. Meanwhile, the distribution of denitrification functional microorganism was corresponding to the function of bioreactor. |
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