Effect Of Temperature On The Stabilization Process And Microbial Community Structureduring Vermicomposting Of Pelletized Sludge

Urban sludge is a product of sewage treatment, a kind of complex heterogeneous body, which make up organic fragments, microorganisms, inorganic particles, colloids and other components, and can easily corrupt to stink, and will cause secondary pollution to the environment if handled improperly. Vermicomposting as an environment friendly, safe and sustainable biological treatment technology is gradually being known to all. During vermicomposting, the effect often depends on whether environmental factors are appropriate, and the temperature is the most important factor and one of the factors easier to be controlled. Temperature not only has a huge impact on both of earthworm growth and reproduction, and metabolic activity, but also plays an important role in the change of metabolic activity and microbial community structure. By influencing the activity of the enzyme, temperature thereby affects the growth rate and substrate utilization of microorganisms, while the temperature also affects some intermediate products' formation rate in organic biochemical reactions and these changes are directly reflected in the microbial community structure. The differences in microbial composition at different temperatures will result in different vermicomposting effects. Based on the above analysis, the urban sewage sludge was regulated into 5mm particles and studied in the following three aspects:?1? the effect of earthworm on physical and chemical indicators of urban sewage sludge at different temperatures;?2? the comprehensive evaluation of effect of temperature on stabilization characteristics of vermicomposting on urban sewage sludge;?3? microbial community structure analysis in urban sewage sludge at different temperatures by PCR-DGGE technology.?1? Studying changes of physicochemical and biochemical indicators in earthworm treatment and control treatment of urban sewage sludge over time under three temperatures, it could be found that the changes of tendency over time in earthworm treatments were substantially the same as control groups respectively under the three temperature conditions. Earthworms accelerated the degradation of organic matter through ingestion and assimilation of organic matter, which would turn organic nitrogen into mineral nitrogen, promoting organic nitrogen mineralization. To the end of the experiment, the MBC and DHA in earthworm treatments were lower than control groups respectively under the three temperatures, indicating that system of the earthworm treatments more stabilized than control groups. Correlation matrix analysis indicates the earthworms can facilitate the process of ammonification and nitrification in the system. Furthermore, the presence of earthworms having improved the microbial biomass carbon?MBC? and accelerated the organic matter?OM? degradation in the early system, results in microbial biomass carbon?MBC? and dehydrogenase?DHA? being low in the latter period, and the stabilization degree of final treated product being higher.?2? The purpose of this study was to elucidate the effects of temperature on vermicomposting stabilization process through comparing the changes of the physicochemical and biochemical indicators in dewatered municipal sludge which was regulated into 5mm particles and inoculated earthworm Eisenia foetida for the experiments at three different temperature conditions?15?, 20?, 25??. The results showed that organic matter?OM?, microbial biomass carbon?MBC? reduced while electrical conductivity?EC?, NH₄⁺-N, NO₃^--N increased with increasing temperature. In addition, dehydrogenase activity?DHA? was not significantly changed with temperature. Furthermore, the results of PCA suggested that stabilization process of vermicomposting had three stages with characteristics including the biological degradation of organic matter, ammonification and nitrification. Raising temperature can contribute to stabilization efficiency of vermicomposting, but does not change the stabilization path.?3?This study aims to explore the changes of microbial populations during vermicomposting at 15?, 20?, 25?were measured by PCR-DGGE technique. The results show that the bacterial and eukaryotic population diversity reduce with temperature increasing, and the increasing temperature can promote the evolution of microbial populations. In the temperature range of 15? to 25?, that temperature can affect the appearing and disappearing of particular microbial populations in vermicomposting system. And temperature has less influence on the dominant microbial populations, which is mainly shown from the fact that the relative quantities of dominant microbial populations increase as well as the relative amounts of shared microorganisms with the increase of temperature. At the end of composting systems, microorganisms degrading cellulose, chitin and other difficult-to-biodegrade organic at three temperatures were dominant, and the higher the temperature was, the larger the relative number was. The system is more stable with refractory organic matter contented.