Study On Microbiology Mechanism Of Methane Reduction And Stabilization In Semi-Aerobic Landfill

In this paper, molecular biological techniques of real-time polymerase chain reaction and denaturing gradient gel electrophoresis and cloning analysis of 16S rRNA and pmoA gene were used to describe community composition and abundance of bacteria in leachate of semi-aerobic and anaerobic landfills, methanotrophs in waste of semi-aerobic landfill. The results as follows:Firstly, the bacterial anoudance and composition in leachate were effceted by different landfill method, the bacterial 16S rRNA copy numbers of the leachate had no significant reduction in initial and stable period. In aerobic landfill, the highest bacterial 16S rRNA gene copy numbers in leachate were found at initial stage, but reduced significantly at stable period. The MOB populations in stabilized leachate were one order of magnitude lower than that of initial ones both in semi-aerobic and anaerobic landfills. More MOB populations existed in semi-aerobic landfill leachate than that of the anaerobic ones.The bacterial diversities of two leachate samples in semi-aerobic landfills were significantly higher than that in anaerobic landfill sites. In addition, bacterial communities in semi-aerobic landfills leachate (both in initial and stable periods) and initial anaerobic leachate had a relatively higher homology with each other, but the bacterial communities in stable anaerobic leachate showed obvious distinguishability.Based on the sequences and phylogenetic analysis, bacterial communities in the tests were classified into six groups:Proteobacteria (about 34.8%), Spirochaetes (about 23.9%), Firmicutes (about 23.9%), Bacteroidetes (about 8.7%) and Thermotoge (about 6.5%). The semi-aerobic leacates had the dominantly higher proportions of Proteobacteria and Bacteroidetes (the contributors to biogeochemical processes) than that in anaerobic ones. Between semi-aerobic leachates, the high similarities of microbial composition were found, but a significantly difference was shown between anaerobic ones. The methanotrophic microbe (Methylocaldum sp.05J-I-7) was only found in semi-aerobic landfills.Secondly, aboudance of MOB was effected by lanfill time, but there was no signicantly inpaction to compostion and divertisity.1# which had the longest landfill time had the highest copy numbers of pmoA genes. The results showed that the quantity of MOB populations had an increasing trend with the landfill time in one-year old wastes, and expressed positive relationship to some extent. It was found MOB of waste around gas pipe all higher than 15m far from gas pipe, It was found MOB of waste around gas pipe all higher than 15m far from gas pipe.The MOB composition and diversity in long landfill time waste higher than short one in different landfill time. There was some difference in one landfill time with the distance to gas pipe, but 4# landfill had a higher similarity. Based on the sequences and phylogenetic analysis, methanotrophic communities in the tests were classified into three groups:Methylocaldum、Methylobacter、Methylocystis.Thirdly, pile surface settlements and volume reduction rate of the semi-aerobic landfills were significantly higher than the anaerobic ones after 5 year landfill disposal.Moreover, the treatments with leachate recycling were tend to have the larger uneven settlements than the ones with water recycling. In different landfill periods, the concentrations of O2 in semi-aerobic landfill piles were significantly higher than anaerobic ones, while the concentrations of CH4 in former were dramatically lower than the latter. VS and TOC content of aged-refuse were obviously lower than the ones in fresh refuse. Moreover, VS and TOC content of aged-refuse in semi-aerobic landfills were significantly lower than that in anaerobic ones, BDM value of aged-refuse in semi-aerobic landfills had a significant reductions comparing with that in anaerobic ones. Furthermore, BDM value of aged-refuse in semi-aerobic landfills increased with air pipe distances and depth increasing, and the greater the air pipe distances, the bigger the difference of BDM value between the layers. In addition, total extraction ratios of humic matters in semi-aerobic aged-refuse were slightly lower than anaerobic ones, while the HA/FA in semi-aerobic and anaerobic aged-refuse were relatively high, and no significant differences were found.