Enhanced biodegradation of polycyclic aromatic hydrocarbons using nonionic surfactants in soil slurry

The effect of nonionic surfactants on the solubility and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the aqueous phase and in the soil slurry phase, as well as the fate of these surfactants, were investigated. The PAH solubility was linearly proportional to the surfactant concentration when above the critical micelle concentration (CMC), and increased as the hydrophile–lipophile balance (HLB) value decreased. Substantial amounts of the sorbed phenanthrene in the soil particles were desorbed by non-ionic surfactants into the liquid phase when the ratio of soil to water was 1:10 (g/ml). Brij 30 was the most biodegradable surfactant tested, showed no substrate inhibition up to a concentration of 1.5 g/l, and was definitely used as a C source by the bacteria. Naphthalene and phenanthrene were completely degraded by phenanthrene-acclimatised cultures within 60 h, but a substantial amount of naphthalene was lost due to volatilization. The limiting step in the soil slurry bioremediation was bioavailability by the micro-organisms for the sand slurry and mass transfer from a solid to aqueous phase in the clay slurry.