An evaluation of the green chelant EDDS to enhance the stability of hydrogen peroxide in the presence of aquifer solids

Hydrogen peroxide is a widely used in situ chemical oxidation reagent which relies on catalysts to generate the suite of reactive species that are required to aggressively remediate contaminated soils and groundwater. In the subsurface environment these catalysts are usually transition metals that are added to the injected solution, or are naturally occurring. Chelating agents are widely used to maintain an adequate dissolved transition metal concentration in near-neutral pH conditions; however, they can also be used to improve the persistence of H2O2 in situations when the aquifer solids have sufficient transition metal content. Ethylenediamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) have been considered to be the most effective chelants and therefore are the most widely used. While previous research efforts have focused on the chelating agent efficiency, the long-term fate of these chelants in the natural subsurface environment is a concern since both EDTA and NTA are non-readily biodegradable. The focus of this investigation was to evaluate the potential of using the environmentally friendly or green chelating agent ethylenediaminedisuccinate (EDDS) as an alternative to EDTA or NTA to suppress the catalytic activity of naturally-occurring transition metals. A series of batch reactor and column experiments were performed using five different aquifer materials and the results demonstrate that EDDS has a comparative chelating efficiency to that of EDTA. The addition of EDDS was able to reduce the H2O2 decomposition rates in the presence of the aquifer materials used in this investigation by 24–97% in well-mixed batch systems, and by 20% and 38% in the column trials where H2O2 was detected in the effluent.