Surfactant production accompanying the modified Fenton oxidation of hydrocarbons in soil

A hydrocarbon-contaminated soil was treated in laboratory slurry reactors using two types of modified Fenton (MF) chemistry. Liquid hydrogen peroxide (HP) with Fe3+ was compared with a calcium peroxide (CaO2)-based oxidant (Cool-Ox™). Bioslurry treatment served as a control. During oxidation, samples of slurry filtrate were tested to quantify hydrocarbon concentrations and bulk surfactant concentrations, using the critical micelle dilution method. The results showed that both oxidants resulted in the temporary accumulation of surfactants to maximum levels of four times the critical micelle concentration, but that surfactants were completely removed by the end of treatment. Removal of surfactants was complete within 2 h for liquid HP treatment versus 2 days for the CaO2-based oxidant. For both MF oxidants, hydrocarbon concentrations in filtrate were 3–4 orders of magnitude greater than in the biological control. Both MF oxidants also showed enhanced removal of the high molecular weight fractions of the petroleum hydrocarbons relative to biological treatment, though this effect was considerably greater with the CaO2-based oxidant. The chemical treatments did not considerably reduce numbers of culturable hydrocarbon-degrading microorganisms relative to the bioreactor, suggesting that chemical and biological oxidation may have occurred simultaneously in the slurry.