Reduction of Nitrate in Agricultural Soils by Bio-electrokinetics

Abstract

High nitrate concentration in surface soils is a serious concern for the agricultural industry throughout the world. Nitrate reduction can be achieved by chemical or biological processes; however, these processes are difficult to achieve in-situ because of the low permeability of clays. This study evaluates bio-electrokinetic processes for nitrate treatment in low-permeability soils. The concept is based on using iron electrodes to generate an electric field and a reducing environment in the soil to facilitate nitrate reduction by existing bacteria. Experiments were conducted using starch as an additive for microbial activity in the anolyte. Three sets of experiments were conducted under 0.5, 1.0, and 2.0 V cm⁻¹ voltage gradient, and using starch as an anolyte for enhancing existing microbial activity in the soil. Initial nitrate concentration in the soil (agricultural soil collected from Jinju, Korea) was between 782 and 800 mg kg⁻¹. Removal of 100% nitrate was achieved in the soil under 0.5 and 1.0 V cm⁻¹ due to the combined effect of biological and iron reduction. A control experiment with iron electrodes, but without starch, was not as effective. Ammonium was also effectively removed by the combined action of starch and iron under 0.5 and 1.0 V cm⁻¹. The role of starch with iron on the nitrate and ammonium removal process is evaluated along with the role of transport by electro-osmosis and electro-migration. The bacterial action on denitrification and nitrification is assessed and the relationship between pH and the efficiency of nitrate reduction in the bio-EK systems is evaluated.

Keywords:

• Agricultural soil
• nitrate reduction
• iron electrode
• starch
• electrokinetics
• bacteria

Acknowledgements

This work was supported by a grant from the Korea government, Ministry of Knowledge Economy. Dr. S. Maruthamuthu thanks CSIR for partial financial support in 12th five year plan under Sustainable Environmental Technology for Chemical and Allied Industries (SETCA).