In Situ Remediation of DNAPLs by coupling cosolvent flushing and hydrogen peroxide: contribution of reductive reactions on contaminant transformation

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In a report released in 2014, the Parliamentary Budget Officer of Canada estimated that, despite two decades of investment in remediation efforts, Canada still has over 22,000 federal hazardous waste sites that will require an additional $4.9 billion of remediation cost. The report also indicated that Dense Non-Aqueous Phase Liquids (DNAPLs), such as chlorinated solvents and polychlorinated biphenyls, were among the most prevalent contaminants at those sites. To date, however, the remediation of DNAPLs has been challenging because these compounds are often located far below the surface, sparingly soluble in water, and relatively recalcitrant. Thus, our research program aims to develop an innovative approach that can expedite DNAPLs removal and reduce remediation cost. The proposed research investigates the efficiency and practicality of a technology that combines cosolvent flushing with hydrogen peroxide (H2O2)-based remediation. In the past, although these two technologies have been used separately for DNAPLs remediation, the idea of combining them into a single treatment technology has received little attention as it was often assumed that they are incompatible (i.e., the oxidant produced from H2O2 will not oxidize the contaminants but will react with the cosolvent instead). However, our kinetics model, built based on a careful review of organic and radical chemistry literature, suggested that in a combined cosolvent/H2O2 system DNAPLs could be effectively removed through unexpected reductive transformation processes. In particular, the model indicated that these transformation processes could be initiated by a series of radical chain reactions whose importance were overlooked in the past. Thus, we propose laboratory experiments to examine whether this is truly the case, and if so, to find ways to make the combined technology more effective and robust for field application. The outcome of this research will be an innovative technology capable of effectively removing DNAPLs, which would reduce remediation cost and human exposure to DNAPLs.