Influence of matured compost inoculation on sewage sludge composting: Enzyme activity, bacterial and fungal community succession

The influence of matured compost inoculation during sewage sludge with sawdust composting was assessed. Mature compost reduced the heating rate, thermophilic phase, peak temperature, and volatile solid degradation rate, with no significant effect on pH and germination index. Matured compost addition also increased the cellulase, peroxidase, arylsulfatase, and urease contents during the mesophilic phase, and increased the urease content but decreased the cellulase, peroxidase, protease, and arylsulfatase contents during the cooling phase, with no significant effect on enzyme activities at the thermophilic phase. Matured compost increased the diversity of bacteria during the mesophilic and thermophilic phases, but reduced the fungal diversity throughout composting. Matured compost significantly improved uniformity of the bacterial community and affected the structure of the bacterial and fungal communities, while changing the correlation between some functional microorganisms and enzyme activities. These results provide guidance for optimizing the composting process when matured compost as bulking agent.