Remediation of chlorinated aliphatic hydrocarbons in groundwater using ZVI and low-voltage DC field: Long-term...

A promising approach for in situ treatment of chlorinated aliphatic hydrocarbons (CAHs) in groundwater combines zero-valent iron (ZVI) with a low-voltage direct current (DC) field. This study compared DC-assisted ZVI remediation with conventional ZVI treatment for tetrachloroethene (PCE) degradation in two identical 3.1m³ sand-filled reactors simulating a three-dimensional aquifer under field-like conditions. Monitoring of PCE, its aqueous and gaseous degradation products, and chloride ions showed consistently higher performance in the DC-assisted system. Total PCE removal was 1.4 times greater, based on chloride mass balance as a robust dechlorination indicator. Cumulative acetylene production, a diagnostic of the β-elimination pathway, was twice as high under DC assistance, confirming a mechanistic enhancement of the more efficient abiotic degradation. Mössbauer spectroscopy indicated a 50% higher content and reduced formation of passivating iron phases. Multiple lines of evidence suggested that the applied electric field enhanced iron reactivity, regulated pH, and facilitated electron transfer, collectively accelerating dechlorination processes. By scaling-up beyond typical laboratory setups, this rare long-term, large-scale study provides critical insights into DC-assisted ZVI performance under realistic subsurface conditions and highlights its potential as a scalable, energy-efficient, and mechanistically optimized technology for in situ remediation of CAH-contaminated aquifers. Environmental Implications Chlorinated aliphatic hydrocarbon (CAH) contamination of aquifers remains a global concern due to the persistence and toxicity of these compounds in groundwater. This study demonstrates that integrating zero-valent iron with a low-voltage direct current field can substantially enhance in situ remediation of CAHs. Large-scale, long-term experiments under field-conditions showed higher PCE degradation and an enhancement of the β-elimination pathway. Acetylene proved a sensitive indicator of enhanced degradation, while chloride mass balance supported improved performance. The ability to manipulate subsurface pH and redox potential offers opportunities for process optimization, supporting DC-assisted ZVI remediation as a scalable, energy-efficient field technology.