Influences of carbonate and chloride ions on persulfate oxidation of trichloroethylene at 20 °C

Application of in situ chemical oxidation (ISCO) involves application of oxidants to contaminants such as trichloroethylene (TCE) in soil or groundwater in place. Successful application of ISCO at a hazardous waste site requires understanding the scavenging reactions that could take place at the site to better optimize the oxidation of target contaminants and identification of site conditions where ISCO using persulfate may not be applicable. Additionally, estimation of the oxidant dose at a site would need identification of groundwater constituents such as alkalinity and chlorides that may scavenge radicals and therefore use up the oxidant that is targeted for the contaminant(s). The objective of this study was to investigate the influence of various levels of chloride and carbonates on persulfate oxidation of TCE at 20 °C under controlled conditions in a laboratory. Based on the results of the laboratory experiments, both chloride and alkalinity were shown to have scavenging effects on the rate of oxidation of TCE. It was found that at a neutral pH, persulfate oxidation of TCE was not affected by the presence of bicarbonate/ carbonate concentrations within the range of 0–9.20 mM. However, the TCE degradation rate was seen to reduce with an increase in the level of carbonate species and at elevated pHs. TCE degradation in the presence of chlorides revealed no effect on the degradation rate especially at chloride levels below 0.2 M. However, at chloride levels greater than 0.2 M, TCE degradation rate was seen to reduce with an increase in the chloride ion concentration. Prior to application of persulfate as an oxidant, a site should be screened for the presence of scavengers to evaluate the potential of meeting target cleanup goals within a desirable timeframe at the site.