Managing Storm Runoff Contamination Using Slow-Release Oxidants: Laboratory Investigations

Managing contamination by urban storm runoff is challenging because of numerous contaminant sources, the first flush phenomenon, and the fast drainage of stormwater by storm sewers. This paper presents the results of laboratory batch, column, and flow-through tests involving a novel in situ chemical oxidation scheme that combines oxidation and slow-release systems to reduce organic pollutants in urban storm runoff. In batch tests, the persulfate/iron system yielded the best overall removal efficiencies for benzene, toluene, ethylbenzene, xylene, and naphthalene, although the removal rates rapidly decreased after 2 to 3 min due to oxidation of ferrous iron in the solution. Slow-release persulfate (SRP), slow-release hydrogen peroxide (SRH), and slow-release Fe²⁺ (SRI) were created by dispersing salts in paraffin wax matrices in a cylindrical mold. Results of column tests indicated that the slow-release forms could release oxidants and Fe²⁺ in a controlled and continuing manner, and the release rates are constrained by the solubility of the dispersed salts and the mixing ratios of the salts and matrices. In the flow-through remedial tests, 89% of naphthalene, ethylbenzene, and xylene, 83% of toluene, and 73% of benzene were removed within 20 min when SRP and SRI were used together. These results suggested that the slow-release oxidants could be installed in multiple storm sewer inlets to rapidly reduce any oxidizable pollutants in storm runoff.