Recognizing the challenges of composting: Critical strategies for control, recycling, and valorization of nitrogen loss

Composting is a simple, efficient, and low-cost resource treatment technology for organic solid waste, which can yield high-quality organic fertilizers and soil conditioners rich in humus. However, inevitable nitrogen loss during nitrogen transformation in composting process results in environmental pollution and product quality reduction. To address this issue, researchers have been focusing on understanding the nitrogen transformation process and implementation measures to enhance nitrogen conservation. Although these studies have reduced the amount of nitrogen loss, the nitrogen that inevitably escapes from the composting system still causes secondary pollution and waste of resources. It is necessary to introduce a comprehensive nitrogen loss control strategy to further solve the problem of nitrogen loss during composting. Therefore, this paper comprehensively reviewed the nitrogen transformation process during composting, nitrogen loss routes, nitrogen loss control strategies, nitrogen recycling and valorization methods, and also suggested the future development trend of composting nitrogen loss control and recycling technology. Finally, this review proposed a new comprehensive nitrogen loss control and recycling strategy for organic solid waste composting including "in-situ control + ectopic recycling + nitrogen valorization", which could provide some guidance for nitrogen resource recovery and secondary pollution control in organic solid waste composting.