Temperature effects for tetrachloroethylene removal with NZVI between 10 and 55 °C in flow-through column experiments

Subsurface utilization for underground thermal energy storage (UTES) in urban areas can promote a sustainable and climate-neutral heat supply. Meanwhile, frequent subsoil contamination raises the question of whether the stored heat could be used for remediation, which can benefit from increased temperatures (e.g., by increased reactivity and desorption processes or enhanced microbial degradation). We focus on nanoscale zerovalent iron (NZVI), which is suitable for chlorinated hydrocarbon remediation. However, the potential benefits or drawbacks of increased temperatures for groundwater remediation, including accelerated contaminant degradation, declining long-term reactivity, or influenced passivation processes by mineral precipitation, remain largely unexplored. Herein, we investigate the effect of temperature changes (10-55 °C) on NZVI's long-term degradation of tetrachloroethylene (PCE) using column experiments to assess the approach's suitability for coupling with UTES. Using demineralized water (DW), maximum PCE removal rates (k_PCE) between 10 and 55 °C increased from 0.13 to 2.3 h^-1. With tap water (TW), k_PCE increased between 10 and 40 °C from 0.18 to 0.75 h^-1. Due to the higher PCE removal rates in combination with increasing H₂ generation caused by enhanced anaerobic corrosion, long-term corrosion reactivity decreased between 10 and 55 °C from ∼275 to 14 d with DW and from 150 to 30 d between 10 and 40 °C with TW, whereby the increased H₂ formation is beneficial for microbial degradation. Accelerated passivation of the NZVI due to carbonate precipitation was not observed for the examined temperatures. Therefore, the experiments revealed that combining UTES with NZVI for remediation purposes is practicable, offering clear remediation advantages.