Catalyzed hydrogen peroxide combined with CO2 sparging for the treatment of contaminated groundwater

• A combined treatment of catalyzed H2O2 oxidation and CO2 sparging is investigated.
• CO2 sparging into the oxidizing solution increases the lifetime of hydrogen peroxide.
• CO2 sparging can enhance the contaminant removal due to stripping.
• The combined process ensures removal rates higher than the traditional process.

In this work we propose and investigate an innovative groundwater remediation option based on the combination of catalyzed hydrogen peroxide (H2O2) with CO2 sparging. The effectiveness of this new process was evaluated by carrying out lab-scale tests on a soil–water system spiked with Methyl Tertiary Butyl Ether (MtBE). The results achieved with the combined process, evaluated in terms of H2O2 lifetime and MtBE residual concentration in the liquid phase, were then compared with those obtained using H2O2 only or amended with KH2PO4 as stabilizing agent. The experimental results showed that the combined H2O2–CO2 process has basically two beneficial effects. On the one hand, fluxing CO2 into the oxidizing solution can lead to a pH decrease to acidic values that enhance the H2O2 stability. Indeed, from the results obtained in the stability tests carried out, it was observed that the hydrogen peroxide lifetime in the combined H2O2–CO2 process proved to be longer than the one achieved in the tests carried out with H2O2 only, although slightly lower than the one achieved using KH2PO4 as stabilizing agent. On the other hand, it was observed that with respect to a traditional chemical oxidation application, the CO2 sparging can further enhance the overall effectiveness of the process as a result of contaminant stripping by CO2. Indeed, the residual MtBE concentration observed after application of the combined H2O2–CO2 process was slightly lower than the ones obtained using H2O2 only or comparable to the one achieved using H2O2 amended with KH2PO4. Overall, these results showed that the combined H2O2–CO2 process could represent a promising alternative to traditional formulations, avoiding the use of chemical amendments, while leading to comparable residual contaminant’s concentration.