Scale-up of hybrid electrokinetic–adsorption technique for removal of heavy metals from contaminated saline-sodic clay soil

Abstract

Bench-scale removal of heavy metals from heavily contaminated saline-sodic soil using hybrid electrokinetic–adsorption (HEKA) cell that employed date palm pit waste based activated carbon have been reported recently. In this study, scale-up HEKA reactor (about 100 folds) was further employed for the removal of Zn, Pb, Cu, Cd, Cr and Hg (concentration ranged 8.82–76.5 mg/kg) from such a soil. The treatment process was operated at fixed voltage gradient of 0.2 V/cm and for a total period of 35 days. Respectively, the achievable heavy metal removal efficiencies of 31.9, 38.1, 55.7, 36.0, 70.2 and 47.4%, were mostly, lower than the respective bench scale removals. The cumulative energy consumption of scale-up reactor was 19.355 kWh, a drastic increase by a factor of 60.94 when compared to that of the bench-scale cell. In contrast, the specific energy consumption (SEC) decreased from 441.12 to 271.477 kWh/m3 due to the increase in the treated soil volume and comparative lower treatment period. Similarly, various parameters influencing the HEKA cell performances changed, significantly. Longer treatment time was expected to have closed the gap with the overall bench scale removal efficiencies, though it would have been at the expense of drastic increase in energy consumption. Rapid degradation of electrolytes at the electrode chambers suggests buffering the electrolyte during treatment to ensure effectiveness of the remediation. The results presented herein demonstrated the feasibility of using HEKA process for removal of heavy metals from saline-sodic soil at larger scale, suggesting its potential for remediation of real contaminated sites. However, site characteristics and complexity associated with EKR process would definitely pose a great challenge in real site implementation of the technique.