The impact of functional membrane covering on nitrogen and sulfur transformation of sludge composting and its microbial action mechanism

Nitrogen and sulfur are essential nutrients for promoting plant growth. Investigating the transformation mechanisms of nitrogen and sulfur during composting has substantial guiding significance for enhancing the fertility of composting products. Functional membrane-covered aerobic composting systems have consistently demonstrated their ability to accelerate compost maturation. However, the transformation mechanisms of nitrogen and sulfur within this system, as well as the associated microbial processes, remain inadequately understood. In this study, the impact of functional membrane coverage (FM) on the transformation of nitrogen and sulfur compounds during sludge composting was studied, along with an investigation into the microbial mechanisms underlying nitrogen and sulfur cycling. The results showed that nitrite ammonification, nitrite oxidation, and nitrate reduction were the main nitrogen transformation steps during the early days of composting. In the middle and later stages, the denitrification intensified, leading to a decrease in available nitrogen content. Sulfate reduction, sulfide oxidation, and thiosulfate dispropotionation constituted the primary sulfur transformation steps, with thiosulfate oxidation intensity gradually increasing. FM inhibited denitrification, sulfite reduction, and thiosulfate dispropotionation, thereby reducing nitrogen and sulfur loss by 14.1 % and 8.1 %, respectively, and increasing available nitrogen and available sulfur content by 14.9 % and 9.6 %, respectively. The main participants involved in nitrogen cycle were Nitrospira, Luteimonas, Streptomyces, Pseudoxanthomonas, Actinomadura, and Pseudomonas. A wide variety of functional microorganisms were involved in the sulfur cycle, with their succession during composting being especially prominent. In summary, the FM system can serve as an effective approach to enhance the fertility of sludge compost products.