The synergistic regulation of sewage sludge biodrying and greenhouse gas reduction by additives

[Display omitted] •Peak temperature and longest high-temperature period achieved by complex additions.•The water content of sludge was reduced to lower than 28.8 % within 21 days.•Additives reduced carbon and nitrogen losses in biodrying processes.•Additives reduced the cumulative emissions of CO2 by 55.41% in biodrying processes.•Highest microbial community richness and stability achieved by complex addition. As a dewatering method of high moisture solid waste sludge, biodrying still faces environmental problems such as material loss and greenhouse gas emission in the process of treatment. In this study, biochar and magnesium chloride were used to explore the synergistic effect of enhancing sludge biodrying and reducing greenhouse gas emissions. The highest temperature of biodrying was raised to 68.2 °C within 3 days, extending the longest high-temperature period to 5 days, which reduced the water content to 28.8 % in the single addition of biochar treatment. The complex addition increased the NH4+-N content of materials by 57.49 % and decreased the NO3–-N content of materials by 40.62 %. The use of additives significantly reduced the emissions of CO2, CH4, and N2O compared to the no-addition treatment. The increase in dominant Actinomycetes and Chloroflexibacter was the main reason for the reduction in gas emissions.