Significance of temperature as a key driver in ZVI PRB applications for PCE degradation

We report on the potential of elevated groundwater temperatures and zero-valent iron permeable reactive barriers (ZVI PRBs), for example, through a combination with underground thermal energy storage (UTES), to achieve enhanced remediation of chlorinated hydrocarbon (CHC) contaminated groundwater. Building on earlier findings concerning deionized solutions, we created a database for mineralized groundwater based on temperature dependence of tetrachloroethylene (PCE) degradation using two popular ZVIs (i.e., Gotthart-Maier cast iron [GM] and ISPAT sponge iron [IS]) in column experiments at 25 °C-70 °C to establish a temperature-dependent ZVI PRB dimensioning approach. Scenario analysis revealed that a heated ZVI PRB system in a moderate temperature range up to 40 °C showed the greatest efficiency, with potential material savings of ~55% to 75%, compared to 10 °C, considering manageability and longevity. With a 25 °C-70 °C temperature increase, rate coefficients of PCE degradation increased from 0.4 ± 0.0 h^-1 to 2.9 ± 2.2 h^-1 (GM) and 0.1 ± 0.1 h^-1 to 1.8 ± 0.0 h^-1 (IS), while TCE rate coefficients increased from 0.6 ± 0.1 h^-1 to 5.1 ± 3.9 h^-1 at GM. Activation energies for PCE degradation yielded 32 kJ mol^-1 (GM) and 56 kJ mol^-1 (IS). Temperature-dependent anaerobic iron corrosion was key in regulating mineral precipitation and passivation of the iron surface as well as porosity reduction due to gas production.