Effects of biochar on bacterial community dynamics and metabolic functions during the composting of food waste digestate

Food waste digestate (FWD), as a low-polluting and high-nutrient waste, has a great potential for resource utilization. Aerobic fermentation composting technology is very suitable for the disposal of FWD, due to its reduction and hygienization characteristics. Biochar can reduce odor emissions and enhance compost quality with its suitable spatial structure and porosity. In this study, the basic physicochemical indexes and microbial abundance of compost were monitored using the windrow composting method, and PICRUSt2 and FAPROTAX were applied to analyze the changes in metabolic functions of microorganisms. The results indicated that biochar prolonged the high-temperature period and improved organic matter degradation. The dominant bacteria in compost were Proteobacteria, Actinobacteriota, Firmicutes and Bacteroidota. Pseudofulvimonas and Burkholderiales are unique to biochar composting and are related to the degradation of composted organic matter and nitrogen cycling. Acidobacteriota positively affected compost decomposition. Gemmatimonadota and Chloroflexi promoted compost decomposition only after biochar addition. Metabolic functional analysis revealed that biochar promoted metabolic pathways and biosynthesis of secondary metabolites. Biochar enhanced the interaction among temperature, electrical conductivity (EC) and pH during FWD composting, which synergistically caused changes in the bacterial community and C/N ratio, further increasing the compost decomposition efficiency. Among these factors, the C/N was the main driver of biochar influence on FWD compost maturation.