Surfactant-enhanced mobilization and biodegradation of polycyclic aromatic hydrocarbons in manufactured gas plant soil

The bioremediation of soil contaminated with polycyclic aromatic hydrocarbons (PAH) often is limited by a low bioavailability of the contaminants. The effect of two nonionic surfactants of the alkylphenolethoxylate type, Arkopal N-300 and Sapogenat T-300, on bioavailability of PAH in manufactured gas plant soil was evaluated in soil columns percolated by recirculating flushing water. Both surfactants enhanced the mass transfer rate of sorbed PAH into the aqueous phase due to solubilization. Solubilized PAH were available for biodegradation. Degradation of the surfactants themselves was monitored by counting cell numbers of surfactant degraders. It could be demonstrated that the rapid degradation of Arkopal N-300 resulted in a lack of oxygen and an inhibition of PAH degradation. Sapogenat T-300 was degraded more slowly, but a depletion of oxygen occurred after 54 d of incubation. Until then the surfactant-enhanced PAH mobilization resulted in an increased PAH degradation as compared to the treatment without surfactant. Therefore, biodegradability of the surfactants was shown to be one of the key functions for the use of surfactants in practice. Reduction of PAH content and toxicity of the contaminated soil was obtained in all cases. Decrease of soil toxicity as indicated by the bioluminescence test was most pronounced in case of the Sapogenat T-300-amended treatment. It is concluded that surfactants can be a useful tool for stimulating biodegradation of PAH in contaminated soil.