Techno-Economic and Environmental Assessment of Magnesium-Impregnated Rice Husk Biochar for Nutrient Removal: A...

This study evaluates the techno-economic and environmental performance of a sequential system based on fixed-bed column adsorption using magnesium-impregnated rice husk biochar (RHB-Mg) for nutrient removal from wastewater, coupled with a prospective assessment of its reuse as a soil amendment in irrigated rice systems. Scale-up based on laboratory data resulted in a treatment capacity of 4.32 m³/day and a biochar requirement of 56.91 kg/day. The system effectively reduced nitrate and phosphate concentrations below regulatory limits under continuous operation, demonstrating high adsorption performance. The techno-economic analysis over a 20-year period revealed that operational costs are primarily driven by magnesium chloride consumption, which strongly influences overall economic feasibility. Life cycle assessment (LCA) identified biochar production as the main environmental hotspot, contributing the highest impacts across multiple categories due to energy demand. Furthermore, literature-supported and LCA-based evidence indicates that the reuse of nutrient-enriched biochar could potentially reduce fertilizer demand (prospective scenario), decrease irrigation requirements, and contribute to a potential climate change benefit through carbon storage, with an estimated reduction of -1.34-kg CO₂ eq per kg of RHB-Mg applied to soil. However, this stage was evaluated as a prospective scenario and was not experimentally validated. Overall, the proposed system demonstrates strong potential within a circular-economy framework; however, process optimization-particularly in reagent consumption and energy integration-is required to enhance large-scale sustainability and economic viability.