Advancing Nitrogen Recovery from Livestock Manure Processing toward a Circular Economy in Agriculture

Livestock manure is a concentrated waste stream that poses significant threats to environmental health. One of the major concerns is the large concentration of nutrients. For example, nitrogen discharged by livestock in feces and urine ranges from 80 to 131 Tg N yr^-1 globally. If harnessed entirely, this nitrogen resource could replace a significant portion of the global demand for fertilizer nitrogen applied to crop fields. However, current manure management practices are inefficient and subject to major losses. In this study, we articulate critical challenges in manure nitrogen management and processing, as well as present an overview of recent advancements in technologies aimed at nitrogen reclamation from livestock manure, including membrane-based technologies and electrochemical techniques. The former achieves excellent total ammoniacal nitrogen recoveries of up to 95%, and the latter can be integrated with membranes or used independently to further enhance nitrogen recovery. We analyze the principles of these novel technologies, present a comprehensive understanding of how they work, and provide a critical evaluation of their strengths and weaknesses. This review provides vital insights on nitrogen recovery from livestock manure, paving the way for a more sustainable future for manure management to achieve a circular economy in agriculture.