Simultaneous removal of nitrate and phosphate in groundwater using Ca-citrate complex

Eutrophication can be caused by excessive input of nutrients, such as nitrate and phosphate, to surface water. Nutrients in groundwater can enter surface water by means of base flow, requiring treatment before they reach surface water bodies. While some studies have attempted to remove nitrate and phosphate, methods for simultaneous removal in groundwater have rarely been reported. In this study, we propose an innovative treatment method to simultaneously remove nitrate and phosphate in groundwater based on an injection of Ca-citrate complex. A total of five batch experiments with different conditions were conducted to identify the removal mechanisms of nitrate and phosphate and to evaluate the use of alternative organic materials, such as lactate. The results showed that Ca-citrate complex can remove nitrate and phosphate simultaneously. Nitrate was removed through denitrification by denitrifying bacteria which used citrate as a carbon source. The removal mechanisms for phosphate were precipitation of phosphate minerals (e.g., hydroxyapatite) and adsorption. The results also showed that reactive materials based on Ca-lactate complex were able to remove nitrate and phosphate. This study suggests that nitrate and phosphate in groundwater can simultaneously be removed using organic-based calcium complexes, proposing a promising remedial method to alleviate potential eutrophication in surface water as well as groundwater contamination.