Reuse of Unavailable Phosphate in Soils Using Solar Cell-Powered Electrokinetic Treatment

Abstract

Electrokinetic treatment (ET) is widely used for soil remediation, specifically for removing heavy metals from soil. Till date, we have focused on the nutrients released in soils using a solar cell-powered ET, which contributes to increasing the productivity of organic farming. Previously, when a 1.5 V solar cell was used in ET, the release of ammonium ions and the growth of microorganisms were observed. However, no release of phosphate ions was observed. Thus, it is presumed that a 1.5 V solar cell is insufficient to release phosphate in soils. Therefore, this study aims to examine the effects of solar cell voltage on the release of phosphate in soils. In laboratory experiments, an anode (oxidation reaction) and a cathode (reduction reaction) were installed in andosol mixed with cow manure compost, and a 3 or 6 V solar cell was used to produce an electric current between the two electrodes. Sixty-two days after the current generation, the chemical properties of the soil were measured. The results suggest that soil redox conditions can be controlled by changing the solar cell voltage. From the pH distributions, a higher voltage of solar cells was used and a large change in pH was obtained. Furthermore, a decrease in soil redox potential was obtained by increasing the solar cell voltage. From the phosphate distributions, a 6 V solar cell is required to release phosphate in soils. It is recommended that applying ET powered by a 6 V solar cell (potential gradient: 0.12 V/cm) facilitates nutrient release in soils, which is the most important factor in organic farming.