| Composting technology has been widely employed to treat municipal sludge. This technology can make the sludge quantity reduction, stabilization and detoxification. Product of compost can be used to produce organic fertilizer. However, the heavy metal containing in the municipal sludge is one of the significantly negative factors which limit application of fertilizer. Therefore, studies on the principle and applied technology of composting for high efficiently utilizing and recycling sludge have important theoretical and practical significance.The aim of this study was to optimize the microbial agent dosage during composting of municipal sludge. Composting experiments were established on the basis of three organic wastes as the raw material, including municipal sludge, spent mushroom compost and waste clay. Three kinds of experiments were designed as follow:inoculum size5%o (w/w); inoculum size10%o; inoculum size15%o. Without microbial agent inoculation was acted as control experiment(CK treatment).The effects of inoculum size on s on physicochemical properties of municipal sludge composting such as temperature, moisture content, pH, conductivity, and concentrations of nitrogen, phosphorus and potassium were investigated in this study. Maturity criterion of sludge such as C/N index and germination index were also monitored during composting. Meanwhile, three-stage BCR(The Community Bureau of Reference) sequential extraction procedure was used to analyze the distribution and migration of heavy metals during composting process. Finally, the microbial community at inoculum sizes of5%o and15%o was investigated in different composting stages by Restriction Fragment Length Polymorphism (RFLP).All the process of composting under four kinds of experiments could be divided into three major steps:a mesophilic-heating phase, a thermophilic phase and a cooling phase. The top composting temperature was increased when inoculated with microbial agent. The heating speed and cooling speed under10%o and15‰treatment were faster than that under5%o and CK treatment. This result showed that high proportion of microbial agent inoculation was beneficial to shorten composting cycle and improve the efficiency of composting. The15‰treatment had the most significant effects on physicochemical property and the second is10‰treatment. The GI of composting was significantly improved by15‰treatment, which meaned that the composting process was promoted.At the end of composting, the percentage of acid exchange fractions and reducible fractions of Cu, Cr, Pb and Zn decreased and the percentage of oxidation fractions and residual fractions of heavy metals increased, showing that composting was an efficient approach for heavy metal stabilization. Compared with control, disposal with microbial agent inoculation obtained good stabilization effects of Cu and Zn. The results suggested that10‰treatment had the most significant effect, followed by15‰treatment. The stabilization effect of Pb and Cr was not obvious under the disposal with microbial agent inoculation.The analysis of RFLP technique showed that the microbial community in different stage of composting has common species and their respective species. The dominant population was in a state of dynamic change. However, Bacillus sp. and Pseudoxanthomonas sp. always existed in the process of composting as dominant population. PCA analysis showed that the inoculation proportion of microbial agent has significant impact on microbial community structure. |
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