Nitrate pollution control in different soils by electrokinetic technology

Previous studies found that a small DC electrical current could attract anions to the anode in sandy soil, even with solute flow towards the cathode. Laboratory experiments were conducted in a vertical, partially saturated column with different soils to determine if nitrate transport could similarly be controlled using electrokinetic (EK) technology. Nitrate concentration, pH value, electrical potential difference, and soil water content were measured for three soils at selected times at different distances from the anode. Constant electrical current was applied to the system for 9 h, and measurements continued for a total of 48 h. The results demonstrated that nitrate can be strongly retained near the anode against gravity in sandy soil with an 80 mA (0.5 mA/cm2) current input. When the percentage of clay in the soil was increased, the EK effect on ion movement decreased; the transport of both ions and water were inhibited by fine clay particles. The loamy soil showed a slight increase in nitrate concentration near the anode, but the clayey soil showed no change. An increase in pH near the cathode was seen in all soils. Water content for sandy soil was higher at the bottom of the column and lower at the top of the column, but for loam and clay soils, the lowest water content was found above the cathode near the bottom of the column. Electrical potential difference between the two electrodes showed that the sandy soil required the highest electrical potential difference to obtain the desired current level; loamy and clayey soils required less. For sandy soil, the highest potential difference was found near the top of the column, but for loam and clay soils, the highest electrical potential difference was measured near the bottom, next to the cathode, suggesting that these locations were the critical zones limiting electrical ion transport.