Sustained release of persulfate from inert inorganic materials for groundwater remediation

Abstract

Groundwater has often been plagued by persistent contaminants such as dense nonaqueous phase liquids (DNAPLs). There is a need for sustained release technologies to ensure long-term treatment in these flow systems. Innovative methods involving sustained release of a selected reagent, persulfate, through pellets made from inorganic materials such as zeolite, diatomite, and silica flour are reported through a proof-of-concept study. Efficacy of the method relies on the preservation of the reagent without decreasing the treatment potential that would otherwise occur with organic matrices. Several methods and different matrix materials for pellet fabrication are described for sustained release of persulfate as a model reagent. Some pellets (diameter: 13 mm; thickness: 2.5–2.7 mm; mass: 0.5 g) show persulfate release of >25 h. Larger pellets are expected to provide longer release times. Different pellet types and fabrication methods offer a range of ease of pellet construction, as well as reagent release times for sustained release. Trichloroethylene (TCE), a DNAPL, was selected as the model contaminant for testing this sustained release approach. Treatment of 15 mg L−1 (ppm) TCE solutions showed 99% degradation, and the pellets remained intact afterwards. The current work demonstrates the potential feasibility of sustained persulfate release from inert matrices for groundwater treatment.