Evaluation of simultaneous removal of nitrate and phosphate in groundwater under flow-through conditions

Nitrate and phosphate in groundwater can be transferred to surface water through base flow, causing environmental problems such as eutrophication. Therefore, it is necessary not only to manage these contaminants in surface water, but also to remove them in groundwater. This study aimed to evaluate the applicability of a treatment method, which uses Ca-citrate complex to simultaneously remove nitrate and phosphate in groundwater, and column experiments were conducted under flow-through conditions. A total of two columns were operated: one column was composed of pure sand and the other was composed of soil, which was collected near Deokjin pond in Jeonju-si, Korea. The influent of the columns contained nitrate and phosphate as contaminants and Ca-citrate complex as a reagent, and changes in geochemistry under flow-through conditions were evaluated. Experimental results showed that nitrate and phosphate were removed in both columns. Nitrate was removed within averages of 0.5 and 0.8 days in the pure sand and soil columns, respectively. Phosphate was not completely removed within the columns; however, it decreased steadily for 88-100% in the first 13 days and 40-45% after 688 days while passing through the columns. It is considered that nitrate was removed by denitrification process, and phosphate was mainly removed by precipitation of hydroxyapatite. In conclusion, nitrate and phosphate can be simultaneously removed under flow-through conditions using Ca-citrate complex. The results from the experiments can be used as a basis for applying Ca-citrate complex to actual field sites.