Effects of agricultural and forestry wastes on humification and its microbially driven mechanisms in kitchen waste composting

Carbon-rich agroforestry auxiliary materials can be regulated to improve the humification and quality in aerobic composting of food wastes. However, it is still unclear on the effects of different auxiliary materials on the humification in food waste composting and their corresponding microbially driven mechanisms, thus limiting the effective selection and utilization of auxiliary materials. Herein, three typical carbon-rich agroforestry auxiliary materials were selected fromdifferent sources, including garden waste, corn straw, and watermelon vine. A systematic investigation was then implemented on their effects and mechanisms on the organic humification in food waste composting. Some parameters were then measured, such as the organic matter fraction, humic substances, and their precursors. Moreover, the high-throughput sequencing and Functional Annotation of Prokaryotic Taxa (FAPROTAX) database were also used to analyze the succession and function of the microbial community during composting. Results showed that the addition of 15% corn straw (wet weight) effectively adjusted the matrix structure to enrich the functional bacteria and thus enhance the compost maturity. Specifically, the watermelon vine with the high protein content was promoted the rapid temperature increase at the beginning of composting, but unfavorable to maintain the thermophilic stage for better product humification. In contrast, the garden waste and corn straw addition were enriching more bacteria (such as Ureibacillus, Bacillus, Oceanobacillus, and Flavobacterium) for the xylan and cellulose degradation at the thermophilic, cooling, and mature stages. Such enrichment in turn promoted the conversion of organic matter into humus precursors (i.e., polyphenols and amino acids) for stable humic acid production. Especially, the corn straw as an auxiliary material promoted the humification by 75%, indicating the accelerated degradation of organic matter. Anyway, the corn straw can be expected to effectively increase the bacteria with the lignocellulosic degradation function.