Evidence for the production of surfactants accompanying the chemical oxidation of hydrocarbons in soils

A hydrocarbon-contaminated soil was treated in laboratory slurry reactors using modified Fenton (MF) chemistry and biodegradation. Treatment with liquid hydrogen peroxide (HP) plus Fe3+ was compared with a calcium peroxide (CaO2)-based MF oxidant (Cool-Ox(TM)). 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 over 4 times the critical micelle concentration, but that surfactants were completely removed by the end of treatment. Removal of surfactants was complete within 2 hours with liquid HP vs. 2 days for the CaO2-based oxidant. For both chemical oxidants, hydrocarbon concentrations in filtrate were 3 to 4 orders of magnitude greater than in the biological control. Both oxidants showed enhanced removal of the high molecular weight fractions of the petroleum hydrocarbons relative to biological treatment, though this effect was greater with the CaO2-based oxidant than with liquid HP. The chemical treatments did not considerably reduce numbers of culturable hydrocarbon-degrading microorganisms suggesting that chemical and biological oxidation can occur simultaneously in soils.