Electrochemically assisted remediation of a highly chlorinated organic polluted sludge: a full-scale case study

Abstract

Electrochemical technology has emerged as an effective method to remediate soils in a laboratory environment. However, its practical application is often challenging due to the complexity of adopting small-scale parameters and identifying all the potential problems during the operation of electrokinetic plants. Here, a prototype demonstration in a space environment (Technology Readiness Level 7) is reported to remediate a 5×5 m² plot of a leachate pond from a landfill containing dense sludge contaminated with chlorinated organic compounds. Bench-scale tests (50 kg per mock-up) were initially carried out to evaluate the effects of the key parameters (electric field, surfactants, and electrode materials) and demonstrated the feasibility of reducing contaminant concentrations in the sludge through dehalogenation and volatilisation. The average electro-osmotic flux was 0.23 cm day^-1, comparable to that reported for silty soils. Iron electrodes enhanced electrokinetic water transport and reduced acidification, while glassy carbon electrodes increased water volatilisation, acidity near the anode, and dehalogenation of chlorinated hydrocarbons. Based on these findings, the full-scale design and operating conditions were selected. After 590 h of operation, the total pollutant concentration was reduced by 34%, mainly due to volatilisation, using a sequence of six iron-electrode arrays at 1 V cm^-1, which increased the sludge temperature over 60 °C. An evaporation rate of 0.021 cm d^-1 and an electro-osmotic flux of 0.62 cm d^-1 were achieved, consistent with the bench tests. These findings demonstrate the potential of electrokinetic plants for the remediation of sludges and provide expertise applicable to future remediation at other contaminated sites.