Hotspots and future trends of phosphorus recycling from livestock manure: A bibliometric review

In recent decades, the importance of managing the earth's dwindling phosphorus (P) has grown exponentially, as have efforts to develop a circular economy. Livestock manure represents a P-rich waste product, so recycling P from livestock manure has garnered the attention of scholars worldwide. Based on a global database from 1978 to 2021, this study presents the current status of recycling P from livestock manure and proposes strategies for efficient P utilization. Unlike traditional review articles, this work establishes a visual collaborative network on P recycling from livestock manure of research areas, countries, institutions, and authors through a bibliometric analysis using Citespace and VOSviewer software. The co-citation analysis of literature revealed the development of the main research content in this field, and further clustering analysis illustrated the current key research directions. Keyword co-occurrence analysis identified the hotspots and new frontiers of research in this field. According to the results, the United States was the most influential and actively contributing nation, and China was the country with the tightest international ties. The most popular research area was environmental science, and the Bioresource Technology published the largest number of papers in this area. The research priority was the technologies development of P recycling from livestock manure, of which the most used method was struvite precipitation and biochar adsorption. Subsequently, evaluation is also essential, including the economic benefits and environmental impacts of the recycling process by life cycle assessment and substance flow analysis, as well as the agronomic efficiency of the recycled products. New directions for technological innovation in recycling P from livestock manure and potential risks in the recycling process are explored. The results of this study may provide a framework for understanding the mechanisms of P utilization in livestock manure, and support the overall popularization of P recycling technology from livestock manure.