Laboratory Testing of the Potential for the Influence of Suspended Sediments on the Electrochemical Remediation of Karst Groundwater

Due to the complicated nature of karst aquifers, many groundwater treatment technologies are difficult to implement successfully. A particular challenge arises because sediments are ubiquitous and mobile in karst systems and may either facilitate contaminant transport or act as long-term substrates for storage via sorption. However, electrochemical remediation is a promising technology to be optimized for karst aquifers due to easy manipulation and control of groundwater chemistry, low cost, ability for in situ application, and performance under alternative power sources. This study investigates the effects of suspended karst sediments on the groundwater electrochemical remediation via electro-Fention (EF) mechanism. The EF mechanism relies on electrochemical (i.e. water electrolysis and ferrous iron release) and electrochemically-induced processes (i.e. Pd catalyzed H2O2 production) to produce hydrogen peroxide and support its activation to hydroxyl radicals - a powerful oxidant capable of degrading and transforming of wide range of contaminants (e.g., chlorinated solvents). Sediments were obtained from different karst locations with a range of concentrations of Fe, Mn and buffering capacities; these sediments were characterized to provide a “library” of substrates for laboratory testing. When the sediments were introduced into the EF experiments, there were adverse effects on the electro-generation of hydrogen peroxide: at steady state (120 min), Pd catalyzed formation of hydrogen peroxide decreased by 60%, 57%, and 75% in the presence of sediment leaching respectively 32, 37, and 33 ppb Fe and 4, 2, and 48 ppb Mn. Presented results imply that while sediments’ presence influences EF mechanism in electrochemical systems, the technology can be optimized in terms of electrode materials, current intensities and current regimes to address these challenges.