Biochar-seeded struvite production from combination of on-farm and industrial wastewater: A review

Struvite (MgNH₄PO₄·6H₂O) is a sustainable, slow-release fertilizer with significant potential for nutrient recycling. However, its large-scale production remains economically constrained due to the high costs of primary components, mainly nitrogen (N), phosphorus (P), and magnesium (Mg). Biochar, on the other hand, is commonly used for soil enrichment and carbon sequestration, which typically lacks sufficient nutrient content to function as a standalone fertilizer. This review explores an integrated approach to struvite production by incorporating biochar and waste-derived resources, specifically, farm waste (rich in N and P) and industrial wastewater (rich in Mg). Surface-modified Mg-biochar functions both as a Mg source and an effective adsorbent, enhancing nutrient adsorption, struvite crystallization, and retention. The review highlights alternative nutrient sources, Mg-biochar preparation methods, nutrient recovery mechanisms on the biochar surface, and the agronomic potential of biochar-struvite composites. This review supports the principles of a circular economy by transforming waste into value-added, slow-release fertilizers. The resulting biochar-struvite composite offers a promising strategy for pollution mitigation, improved crop productivity and sustainable nutrient management.