Researches On The Communities, Functions And Applications Of Microorganisms In Compost Based On Molecular Biological Techniques

Composting is a promising technology which can simultaneously achieve the reduction, reclamation and safe treatment of organic municipal solid waste (MSW). The most important thing for the promotion of composting in MSW treatment is to improve the composting efficiency and the quality of compost since the long composting cycle and the low quality of compost have restricted the application of composting in China. Microorganism is the major biological factor in a composting system. An understanding of the microbial community structure, the population dynamics and the functions of microbes will provide us important microbiological knowledge for the improvement of composting. With the help of modern molecular biology techniques, researchers can study microorganisms without culturing them, and by using molecular biology techniques, such as polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), real-time fluorescence quantitative PCR (qPCR) and DNA sequencing, researchers can obtain the microbial community structure and the population dynamics promptly, which is very important for the the improvement of composting.In this paper, molecular biology techniques, combinated with culture method, was applied for investigating the microbial community in compost system, and the information about the microbial community was used as basic kwonledge for the improvement of composting technology.Traditional composting method was used for composting kitchen discards that manually separated from MSW, and composting was proved to be good compost materials. Among the degraded organic matters during the active composting phases, more than60%of them were degraded in the high-temperature phase, which indicated that the high-temperature phase is the most important phsase for the degradation of organic matters. PCR, DGGE and DNA sequencing were applied for investigating the microbial community of samples from the high-temperature phase, and the analysis results of16/18S rDNA sequence showed a relatively abvious dynamics of the microbial community. The studies also showed that, in the samples from the high-temperature phase, the dominant bacteria, the dominant actinomysetes and the dominnat fungi are Bacillus spp., Streptomyces spp. and Nocardia spp., and Aspergillus spp., respectively.Based on the study results above, the paper proposed a new method of continuously thermophilic composting (CTC), which composted the materials under high-temperature (>50℃) during the whole composting process. Four runs with different operation manner were compared with a traditional composting run. The run which directly heated the materials to50℃without any other temperature control showed the fastest speed of degradation and matured in14days, while the composting cycle of traditional run was28days. On the basis of research results above, the paper suggested an effective CTC method as follows:heat the materials up to50℃in the initial phase of compossting, maintain the pile temperature at least at50℃, keep a moisture content of60%, supply a gas flow of0.25L/(min-kg) and turn the pile daily.With the help of PCR, DGGE and DNA sequencing, qPCR and traditional culture techniques, the paper investigated the microbial community in the traditional composting process and the CTC process. The study showed that the CTC methods decreased the diversity of bacterial community and increased the numbers of bacteria, and the major dominant bacteria are Bacillus spp.. The study also showd that the CTC methods increased the diversity of actinomycetes and the numbers of actinomycetes, and the dominant actinomycetes are Streptomyces spp., Mocromonospora spp., Amycolatopsis spp. and some other thermophilic actinomycetes. In addition, the CTC methods might have suppressed the growth of fungi.In the study, suspension of soil and compost samples from high-temperature phase was used as source inouculant and the suspension was mixed with rice straw and chips, which were used as a medium. The mixture was cultured in a water bath at55℃for30days. A medium with sodium salt of carboxymethyl cellulose was used for separation of cellulolytic thermophiles from the culture mixture. Fifteen strains were selected from the cultured thermophiles after determine their degradation ability on a medium with cellulose and Congo red. Among the15strains,13strains were97%identical to Bacillus spp., one strain was97%identical to Brevibacillus borstelensis, and one strain was80%identical to Paenibacillus sp., which was determined by the biochemical or physiological identidication, the morphology characterization and the analysis of16S rDNA sequence. Each cultured strain with a volume of5mL/(kg compost) was inoculated into pile PA, with a negative control PN. The results showed a faster decrease of total organic carbon and a less loss of nitrogen in pile PA. The results also showed that pile PA matured six days earlier than pile PN, which suggested that a inoculation have spped up the mature process. The inoculant also had speed up the degradation of cellulose and hemicellulose.