Enhanced desorption and biodegradation of phenanthrene in soil-water systems with the presence of anionic-nonionic mixed surfactants

The effects of anionic-nonionic mixed surfactants, sodium dodecyl sulfate (SDS) mixed with Triton X-100 (TX100), on the desorption and biodegradation of phenanthrene in soil-water system were investigated in an aim to improve the efficiency of surfactant bioremediation technology. Results indicated that the presence of SDS not only increased the solubilization of TX100 for phenanthrene, but also reduced the sorption of TX100 onto soils. As a result, the desorption efficiency of phenanthrene from the contaminated soil was greatly enhanced by mixed surfactant solutions compared with that by single TX100 solution and appeared to be positively related with the mole fraction of SDS in solution. Mixed surfactants with relatively smaller ratio promoted phenanthrene biodegradation, for example, the biodegradation percentage of phenanthrene in 1:9 SDS-TX100 mixed solutions was about 165% of that in the single TX100 solution at the same TX100 concentration of 1.6 mmol/L in 24 h. But the biodegradation was inhibited with larger ratio of SDS in the mixed solutions, which may be due to the preferential utilization of SDS by phenanthrene degraders. Thus, the selection of mixed surfactants should consider simultaneously the effects of SDS on desorption and biodegradation. The experimental results can be used to provide valuable information in designing the surfactant bioremediation technology for contaminated soils. (c) 2006 Elsevier B.V. All rights reserved.