Product characterization, application, and techno-economic aspects of phosphorus recovery as struvite from swine wastewater: A case of small-scale swine farm

This study investigated phosphorus recovery from swine wastewater using chemical crystallization, focusing on the quantity and quality of the recovered product, crystal characteristics, phosphate release, and techno-economic feasibility for small-scale swine farms. Phosphate recovery efficiency exceeded 80 % when the pH was above 8.0, with solid precipitates containing 9.5–12.8%P dry weight. Approximately 65 % of phosphorus was recovered as struvite at pH 8.5 with a Mg/P molar ratio of 1.95. Treating 15.47 m³·d⁻¹ of swine wastewater for struvite production yielded at 10.95 kg·d⁻¹ of struvite, equivalent to 1.28 kg P·d⁻¹. Recovered struvite exhibited a cumulative phosphate release at 50.56 % by day 30, making it suitable as a slow-release fertilizer compared to monoammonium phosphate (65.55 %) and triple superphosphate (61.96 %). The techno-economic assessment for small-scale swine farms covered five main components of the struvite production system and evaluated four scenarios. The results indicated the lowest total operating and capital costs were 2769.96 USD·y⁻¹ and 3943.10 USD, respectively. Revenue from struvite was estimated at 3778.04 USD, with a unit production cost of 6.56 USD·kg P⁻¹. The struvite production system on full-scale swine farms offers a moderate and competitive cost compared to other chemical precipitation processes. The shortest payback period for the struvite production system was 3.91 years. Sensitivity analysis revealed that increased costs or reduced income would extend the payback period by approximately 18 % for all scenarios. This study demonstrated a practical method for recovering phosphorus, promoting sustainable phosphorus management, environmental protection, and supporting the circular economy in human ecosystem and sustainable food security.