Effect Of Earthworms On Microbial Biomass、microbial Activity And Microbial Community During Vermicomposting Of Municipal Sludge

Municipal sludge is as an inevitable byproduct from wastewater treatment plant. It is characterized by high water content and organic material, which lead to microorganisms proliferate. Large amount of harmful gases such as ammonia, hydrogen sulfide and mercaptans, is released from sludge, especially under anaerobic condition, which bring about kinds of environmental pollution problems related. However, municipal sludge is rich in high nutrients(nitrogen, phosphorus and potassium) available for plant. It should be noted that stabilized treatment process is required before further disposal and use.Vermicomposting, as a biochemical treatment method for managing different types of organic wastes, is conducted by joint action between earthworms and microbes to transform organic matter into relative stable product. Dewatered sludge cannot directly composted as the substrate, because it easily generates the leachate with toxicants and gives rise to an anaerobic environment where earthworms cannot survive. It is hypothesized that bulking sludge is pelletized, which offers an essential condition for the growth of earthworms. Hence, the cumbersome blending bulking materials may be omitted prior to vermicomposting. Despite earthworms is a leader of fauna and microbes in vermicomposting system, microorganisms play more important role in degrading organic material than earthworms. Therefore, in vermicomposting system, the examination with respect to microbial profiles of activity, number and community is of significance and importance, because this can well clarify the underlying mechanism regarding the decomposition and stabilization of organic substance during vermicomposting process. As mentioned above, the main objective of this study is to evaluate stabilization process during vermicomposting of dewatered sludge, to examine the changes of microbial community composition employing polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE) and sequencing technology and to investigate the effect of temperature on microbial biomass, activity and community of vermicomposted products.Firstly, earthworms can enhance stabilization of organic materials in pelletized sludge. Inoculation of earthworms elevate microbial biomass carbon and its activity, thus fasten decomposition and transformation of organic matter, showing higher stabilization degree of finial vermicomposted product.Secondly, vermicomposting of dewatered sludge should be consisted of four steps, including the startup stage, the active stage, the continuous stage of degradation and the stable stage. The vermistabilization rate of pelletized sludge in the small system seemed to be faster in comparison to the large one. Earthworms activity lead to greater influence on eukaryotic microbial community than bacterial community from DGGE images of both treatment systems. Decline trends of bacterial community diversity were detected during the whole process of vermicomposting because of disappearance of many degradation bacterium in later stages, such as Chitinophaga sp., Flavobacterium succinicans, uncultured Saprospiraceae bacterium, uncultured Flavobacteriia bacterium, which suggests complex organic materials utilized by microorganisms above decomposed basically. Moreover, bacterium Ochrobactrum sp. and Nitrosomonas halophila, characterized by transforming nitrogen element emerged from 50 day of experiment, maybe indicating achievement of maturated products. From the view point of eukaryotic community, many molds be capable of decomposing the complex compounds were founded during the vermicomposting process of sludge. Additionally, Flavobacteria, Sphingobacteria and Cercozoa, as well as the Molds were dominated during vermicomposting of sludge. Based on analysis of MBC, DHA and DGGE finger images during the whole treatment period, vermistabilization of sludge is completed by combined action between earthworms feeding behavior and some microbes specialized for degradation of organic matter.Thirdly, in temperature experiment, MBC and DHA presented a similar trend. That is to say, in first 20 days MBC and DHA descended rapidly, then kept a lesser fluctuation until the end. Remarkably, the lowest value in MBC and DHA were exhibited under 25°C condition, indicating best stabilization degree of vermicompost. Similarly, bacteria and antinomyces numbers of finial products were also in accordance with the results of MBC and DHA. Analysis of PCR-DGGE show that higher bacteria populations diversity were seen in vermicomposts of three temperatures systems than initial sludge system. Although microbial biomass(bacterial number) decreased, its community diversity increased, which elucidated that vermicomposting system possess abundant ability of organic matter decomposition. Moreover, lower value of bacteria populations diversity in 25°C system may be attributed to intensified earthworms activity in higher temperature. Cluster analysis present similar bacterial community in 15°C and 20°C experiment systems, in contrast to 25°C vermicomposting treatment. Sequencing results account for loss of nitrogen due to the appearance of great amount of bacteria A. echinorum in 25°C vermicomposted product, and stronger biochemical reaction because of presence of Acidobacteria bacterium IGE-004 related to decomposition of complex organic matter. Moreover, effect of temperataure on eukaryotic microbes is more significant than bacterial community. Additionally, eukaryotic microorganisms E. tuberculata and Pyxidiophora sp. 03 flourished in all vermicomposted products. For fungi, T. virginica, A. macrocystis, Pyxidiophora sp. as an Ascomycetes be capable of degradating complex compounds were influenced by temperature, especially Pyxidiophora sp..