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Effect of thermotolerant bacterial inoculation on the microbial community during sludge composting.

A thermophilic bacterium (Geobacillus stearothermophilus CHB1) was inoculated in sludge compost, and effects of the inoculation on the bacterial abundance and community structure in sludge compost were investigated using quantitative PCR and Illumina Miseq sequencing. The results showed that the high temperature stage (>50ºC) of CHB1 and the CK (control without inoculum) piles started on the 5th and the 8th day, and lasted for 7 and 2 days, respectively, indicating the extension of thermophilic phase by CHB1 inoculation in the sludge compost. At the end of the composting, the CHB1 piles showed a higher loss of total organic carbon, lower C/N ratio, and moisture content. The bacterial abundances in the CHB1 piles were significantly higher in the heating and thermophilic phase, however, lower than those of the CK in the cooling phase of composting. The richness and diversity of the bacterial community in the thermophilic phase increased after inoculation with CHB1. After inoculation of CHB1, there were higher relative abundances of Firmicutes, Thermopolyspora, Thermobacillus, Thermomonas, Thermomonospora, and Thermovum, which could grow in the high-temperature environment. Furthermore, redundancy analysis indicated that total organic carbon, total nitrogen, C/N ratio, pH, temperature, and moisture were the significant parameters that affected the bacterial community structure during sludge composting. Our findings suggested that inoculation with CHB1 would enhance the quality and efficiency of composting.