Pilot-scale study on in situ electrokinetic removal of nitrate from greenhouse soil

Abstract

In greenhouses, excessive nutrients generally accumulate in the soil, which may induce adverse effects on crop yield and quality. In situ electrokinetic (EK) tests were conducted on a pilot-scale to remove nitrate from greenhouse soil for 64 days using a specially designed electrode module. When a pair of electrodes was installed horizontally in the furrows (EK pilot test I), a significant amount of nitrate was removed by electromigration towards the anode although the electroosmotic flow was not obtained. In the other test (EK pilot test II), where two anodes and one cathode were placed in the furrows and under the ridge, respectively, the efficiency of nitrate removal was comparable with that in the EK pilot test I. However, the removal pattern was asymmetric with respect to the cathode because soil heterogeneity affected the main transport mechanism, electromigration or electroosmosis, depending on location. After the EK treatment the overall efficiency of the nitrate removal was >90% in both tests. The main cation, K + was also removed, and thereby the electrical conductivity of the soil was reduced up to 87%. The energy consumed for the EK pilot test I operation was much lower than that used in the EK pilot test II. During the EK tests, indigenous nitrate reducing bacteria were introduced to enhance nitrate biodegradability but the effect of bio-augmentation was insignificant. From the results it can be concluded the EK technology is feasible to remove salts from greenhouse soils and the EK pilot system I is more applicable to greenhouse soil remediation. However, there is still a room for improvement to achieve a successful field application.