Integrated method of electrochemical dechlorination of chlorinated aliphatic hydrocarbons in combination with groundwater pumping in highly contaminated groundwater – field application

Abstract

The study deals with the electrochemical degradation of chlorinated aliphatic hydrocarbons (CAHs) at a highly contaminated site. After previous conventional remediation interventions with low efficiency, pilot test was conducted at the site using a progressive method of CAHs electrochemical dechlorination, along with technical optimizations to increase dechlorination efficiency. Pilot test was divided into two phases, each using a different electrode arrangement to identify the optimal configurations for enhancing remediation efficiency. Linear electrode arrangement with a predominance of anodes reached 70–98% degradation efficiency during the 1^st stage. Iron anodes proved more effective than iron cathodes, reaching maximum dechlorination efficiency of 78%. A significant increase in CAHs concentration in one of the most contaminated well indicated significant effects of direct current (DC) on dense non-aquatic phase liquids (DNAPL) movement and distribution, suggesting a link between electrokinetic phenomena and DNAPL migration. After certain time without DC, the 2^nd stage was implemented with triangular electrode arrangement along with pulsed pumping of highly contaminated groundwater. The triangular electrode arrangement was focused to decrease contamination around critically contaminated well where the presence of DNAPL was expected. Pumping sub-stage with anodes situated as outer electrode triangle confirmed the higher efficiency of anodes in the degradation of CAHs. The improvement by pumping increased the degradation rate by about 10–30% depending on the well compared to the non-pumped sub-stage. Nevertheless, triangular arrangement did not reach higher degradation efficiencies compared to linear arrangement. Oxidation-reduction potential (ORP) played a significant role in CAHs removal.