Remediation of LNAPLs by In Situ Chemical Oxidation: The Case of Toluene Oxidation by Activated Persulfate

Abstract:

The importance of groundwater to the prosperity of North American societies is profound, since a large percentage of the population relies on this valuable resource. However, groundwater is often contaminated by leaking underground storage tanks; the latter is the primary cause of LNAPL contamination. Toluene is a common industrial solvent and a main component in gasoline, which is often found at LNAPL contaminated sites.

A prominent technology to remediate LNAPL contaminated sites is in situ chemical oxidation (ISCO), whereby oxidants are delivered to the subsurface to transform the dissolved contaminant to benign products and restore the environment. Recently, persulfate has been proposed as an effective and persistent oxidant. Persulfate can be activated to produce stronger oxidants, namely sulfate radicals, that enhance the degradation rates of contaminants in solution.

The aim of this work was to improve our understanding of ISCO by unraveling the underlying mechanisms of toluene degradation using thermally activated persulfate. We conducted a series of batch experiments to estimate the toluene degradation kinetics and to identify the degradation by-products. Further, to understand the application of ISCO, we studied toluene LNAPL degradation in a glass replicate of a fractured rock.

Hereby, we report on the formation of solid and gaseous by-products as well as the potential for sequestration of toluene LNAPL due to these by-products, hindering remediation efforts. Our findings allow us to better design and apply ISCO and, thus, remediate the subsurface.