Ca-citrate as a reagent for simultaneous removal of nitrate and phosphate from groundwater and surface water

Nutrients such as nitrate and phosphate can enter aquatic systems through surface runoff and groundwater flow, which may cause eutrophication. To alleviate this environmental problem, removal of nutrients from both groundwater and surface water is required. The purpose of this study was to develop a chemical reagent and to evaluate its effectiveness at removing nitrate and phosphate. Ca-citrate was proposed as a chemical reagent and was prepared in its solid form that can be applied to both groundwater and surface water. A batch experiment was conducted to confirm the feasibility of simultaneously removing nitrate and phosphate. The experimental results showed that nitrate concentrations were reduced from 11.16 mmol L⁻¹ to 0.01 mmol L⁻¹ after 48 h. The formation of nitrite suggested that denitrification is the mechanism by which nitrate is removed. The concentration of phosphate decreased from 10.35 mmol L⁻¹ to 0.53 mmol L⁻¹ over 120 h. Visual inspection of white precipitates and calculation of saturation indices indicated that phosphate was removed via precipitation of hydroxyapatite, a Ca-phosphate mineral. This study suggests that the solid form of Ca-citrate may be used as a reagent to simultaneously remove nitrate and phosphate from groundwater and surface water.