IMPROVEMENT OF DENITRIFICATION PERFORMANCE USING LIMESTONE IN THE ARTIFICIAL RECHARGE FACILITY

High nitrate concentrations are frequently observed in groundwater. Concentrations are generally high in the area where intensive infiltration takes place such as LID or artificial recharge facilities. Artificial introduction of nitrate-rich groundwater to the deep aquifer can also cause adverse effects due to geochemical disturbances . In this study, we performed experiments effectively removing nitrate in the infiltrating water using three columns packed with sand 100% (Column A), sand 97% + woodchip 3% (Column B), and sand 96.4% + woodchip 3% + limestone 0.6% (Column C). The sands used for these experiments were collected from the local coastal beach and treated with HCl solutions to completely remove CaCO₃ materials. Each column was filled with KNO₃ solution (20 mg-N/L) and the water level at the top of each column was maintained as constant. At designated times, 150 ml of pore water was sampled for measurement of pH, EC, Eh, DO, alkalinity, DOC, NO₃^-, NO₂^-, NH₄⁺, F^-, Cl^-, SO₄^2-, Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe, and Mn, and precisely investigated the chemical reactions influencing the denitrification. We found out that the decomposition of organic matter plays as the electron donor in inducing denitrification. However, the CO₂ generated from the organic matter lowers the pH to a level (<5.5), which can suppress the denitrification to a large extent (Column B). When limestone was used together with the organic matter (Column C), it avoids the severe decrease in pH and its denitrification was 3 times faster than that obtained from the column without limestone (Column B).

This work was supported by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry(IPET) through ‘Development of a low impact development facility customized in rural area using agricultural byproducts’ Program (or Project), funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (grant number 320052-3).