Modeling and Optimization of Phosphate Recovery from Industrial Wastewater and Precipitation of Solid Fertilizer using Experimental Design Methodology

Phosphorus (P) is one of the primary nutrients generating eutrophication in aquatic systems1. To prevent eutrophication, municipal or agricultural wastewaters are treated to reduce the phosphorus concentrations in the wastewater reaching surface water streams. While unregulated P is a pollutant in a water body, phosphorous is a useful resource in agricultural fertilizers, food supply, and industrial raw materials1–3. Unfortunately, phosphorous resources have mostly been obtained from minerals that will definitely be limited by the recent enormous utilization. Based on a previous study4, phosphorous mineral resources are economically feasible for only 50 years. Therefore, P recovery from wastewater can be advantageous with respect to preventing water pollution, removing scales on the inner surface of pumps and pipes, facilitating successive treatment steps, and preventing the devastation of mineral resources4,5. Successful P recovery should require an effective nucleation and growth of struvite crystals so that desirable amounts of precipitated struvite can be recovered typically through the gravitational settling process. However, there are challenges to overcome; for example, calcium ions (Ca2+), of which the typical concentrations are 30–60 mg L–1 in municipal wastewater plants, are known as representative ions that hamper struvite crystal nucleation and growth6. Calcium ions actively react with phosphate to form calcium phosphates. Previous studies on the influence of calcium on struvite crystallization reported that Calcium ions with struvite co-precipitation can retard the nucleation induction and inhibit the growth for struvite crystal formation6,7. However, calcium, as an impurity, could be a negative factor for struvite formation. Calcium presence at high levels in synthesized wastewater would inhibit struvite formation, because calcium-phosphorus precipitates could also be formed. In theory, struvite precipitation could occur in wastewater effluent if phosphorus were released into solution, as reactive phosphate ions, and become available for struvite formation. In this study, Modeling and Optimization of Phosphate Recovery from Industrial Wastewater and Precipitation of Solid Fertilizer using Experimental Design Methodology