Recovery of phosphorus and nitrogen from domestic wastewater by using dolomite rock through struvite precipitation

The increasing discharge of phosphorus (P) and nitrogen (N) from domestic wastewater contributes to eutrophication, resource loss, and environmental deterioration. Conventional nutrient removal Methods are expensive and rely on chemical inputs, emphasizing the need for low-cost and sustainable recovery options. This study investigates the possibilities of locally available Ethiopian dolomite rock as a natural magnesium source for recovering phosphorus and nitrogen through struvite precipitation. The objectives were to characterize the dolomite and wastewater, optimize struvite formation conditions, evaluate nutrient recovery efficiency, and assess the chemical composition and safety of the recovered product. To release Mg2⁺, dolomite was dissolved in 2 M HCl at a 25% solid-to-liquid ratio. The solution was then mixed with domestic wastewater at pH 8 in different volumetric ratios. The original wastewater included 1.65 mg/L PO₄3⁻−P and 19.4 mg/L NH₄⁺−N. The optimal nutrient ratio was 50:70 mL wastewater-to-dolomite solution, resulting in 100% phosphorus and 88.75% nitrogen removal. The recovered precipitate contained 2.66% P, 1.01% N, 2.58% Mg, and 11.77% Ca, indicating good nutrient capture but with calcium co-precipitation, reducing product purity. Heavy metals such as As, Ni, Cr, Zn, and Cu were below detection limits, indicating safe for agricultural application. Although large quantities of calcium and chloride remained in the filtrate, process demonstrated strong potential for producing a low-cost, eco-friendly fertilizer while reducing nutrient pollution. Overall, Ethiopian dolomite is a feasible magnesium source for nutrient recovery and promotes proper wastewater management in resource-limited settings.