Study On Microbial Population Structure Successional Changes During Sludge Composting Process

In this research, the forced aeration composting technique was used for composting of digested sludge from municipal sewage treatment plant, analyzed the changing rules of physical, chemical and biological indicators during the sludge composting process, Combined with the method of the conventional microbial culture, PCR-DGGE and gene sequencing technology to analyze the diversity of microbial population and the succession changes of the microbial population structure, studied the successional changing rules of microbial population, also discussed the relationship between the physical and chemical characteristic changes and the microbial population structure changes, and the Gene sequencing identified the part of microbial populations which were in a dominant position in the process of composting. The following results have been obtained:In different seasons, sludge was mixed with sawdust pro rata in different volume ratios, which were sludge to sawdust 2:1, sludge to sawdust 1.5:1, sludge to sawdust to regurgitant sludge 2:1:1, sludge to sawdust 1:1 and sludge to sawdust 1.5:1.These five groups of composting test could reach the set temperature (60℃). All of the initial five days of the test, the highest temperatures respectively attained 63℃, 68℃, 68℃, 62℃and 66℃, and maintained 6d, 5d, 6d, 6d and 10d separately. The records of temperature,moisture,organic matter,pH,total nitrogen and ammonia nitrogen with time that showed the composting could be successfully processed. At the end of the composting, moisture, organic matter and total nitrogen decreased obviously; pH and ammonia nitrogen first increased and then decreased during the composting process; conductivity and nitrate nitrogen increased first and were at the state of stability afterward; The cress seed germination index (GI), used as indicator of phytotoxicity and maturation of compost , exhibited that the sludge compost was almost stabilized and mature near the 40th day of composting , when 77.96%, 90.12%,94.40%,93.74% and 88.63% of GI were obtained respectively.Conventional culture microbial (bacteria count method) studies showed that, in the beginning of composting, bacteria is the largest number of microbial in the whole process, about 108-109 CFU/ g dry sludge, it is the dominant microbial population during the process of composting, and the number of fungi and actinomycetes were relatively small, about 2-4 orders of magnitude lower than the bacteria, bacteria,fungi and actinomycetes were large breeding in the warming period of composting, and begin decreasing after the high temperature period. In addition, E. Coli ,as a common indicator of pathogens in sludge , reduced greatly from the order of 107-108 to 10-102 in the final examination of the compost, and the kill rate of Belly worm nit reached 95 to 100 percent, which had been up to the national standard.The result of PCR-DGGE and gene sequencing research indicates that different microbial populations live in the dominant position in the different times of composting. With the changes of the composting temperature, the structure of microbial population changed at the same time, and stabilized at the end of the composting. Gene sequencing for the dominant microbial populations at different periods, obtained 12 kinds of microbial populations, such as uncultured compost bacterium clone 2B09 16S ribosomal RNA gene, and so on.