Effects of composite microbial agent with straw or sawdust on organic matter degradation, enzyme activity and functional genes during aerobic composting of food waste

Bulking agent and microbial agent are widely used to improving the aerobic composting condition. This study aimed to evaluate the effects of composite microbial agent which is consisted of Azotobacter salinestris, Aspergillus oryzae, Bacillus licheniformis, Bacillus cereus and Trichoderma viride with different bulking agents (straw or sawdust) on organic matter degradation, enzyme activities, and functional genes associated with carbon and nitrogen cycling during aerobic composting of food waste. The results demonstrated that the inoculation of composite microbial agent significantly improved the degradation of starch, protein, cellulose, and grease, along with boosting microbial enzyme activity and the abundance of carbon degradation genes. Furthermore, the degradation of organic matter (OM), protein, cellulose, and grease were higher in the straw bulked composting with composite microbial agent treatment (B). Meanwhile, B also exhibited a higher abundance of cdh and rbcL genes compared to the other treatments. Pearson regression analysis identified temperature as the primary factor controlling organic matter degradation, while cdh and cex genes exhibited strong associations with cellulose degradation during food waste composting. These findings suggest that incorporating straw as bulking agent with composite microbial agent during food waste composting can effectively enhance organic matter degradation.