Disparities and mechanisms of carbon and nitrogen conversion during food waste composting with different bulking agents

The low C/N ratio, high moisture content, and low porosity of food waste require the addition of bulking agents for adjustment during the composting process. However, the effect and mechanism of different bulking agents on the reduction of carbon and nitrogen losses are unclear. Therefore, this study conducted experiments to evaluate and clarify the differences in carbon and nitrogen transformation between sawdust, rice husk and wheat bran in food waste composting. The results showed that the addition of bulking agents promoted the conversion of carbon and nitrogen into total organic carbon (TOC) and total organic nitrogen (TON) rather than CO2 and NH3. The carbon and nitrogen losses were reduced by 16.00-25.71% and 11.56-29.54%, respectively. Notably, the Sawdust group exhibited the highest carbon retention, whereas the Wheat_bran group demonstrated superior nitrogen retention. The succession of bacterial communities showed that sawdust enhanced the cellulolysis and xylanolysis functions while wheat bran promoted nitrogen fixation. Correlation analysis was further employed to speculate on potential interactions among carbon and nitrogen components. The incorporation of sawdust and rice husk improved humification partly due to the addition of lignocellulose and the accumulation of total dissolved nitrogen (DTN) in the substrate, respectively. In the process of ammonia assimilation, the addition of wheat bran promoted the accumulation of dissolved organic carbon (DOC), contributing to the synthesis of TON to a degree. These findings offer cost-effective strategies for conserving carbon and nitrogen from loss in food waste composting by selecting suitable bulking agents, ultimately producing high-quality fertilizer.