Remediation of Weathered Crude Oil Contaminated Soil with a Green Surfactant, Alkyl Polyglucoside |
In present study, a green surfactant, alkyl polyglucoside, was tested in washing weathered crude oil contaminated soil. Weathered crude oil contaminated soils, which are much more difficult to remediate than freshly contaminated soils, are widespread all over the world especially at the sites of oil fields ,refineries and many other chemical industries. Surfactant enhanced ex-situ soil washing can be used to remediate crude oil contaminated soils. However, the toxicity of the surfactant is one of the major concerns of the technology. In present paper, the washing of weathered crude oil contaminated soil collected From Hugochem, was studied using solutions of alkyl polyglucosides ( APGs).
APGs are a Group of nonionic surfactants which are produced from naturally occurring renewable resources and readily biodegradable with little environmental toxicity. Solutions of two APG products, APG0810 and APG1214 (0.5 to 2.0%), were tested in washing the weathered crude oil contaminated soil. APG1214, with longer alkyl chain, was much more effective in removing crude oil from the weathered soil than APG0810. The oil removal was improved by adding inorganic sodium salts into APG1214 solutions, and a best inorganic salts formula was obtained using the simplex-lattice design and its corresponding model. To optimize the washing conditions, the effects of temperature (40 to 90℃), washing time (5 t0 60 min) , agitation speed (130 to 450 rpm) and solution/soil ratio (2. 5 t0 25mLg-l) were investigated respectively, and the values of the parameters were optimized with an orthogonal experimental design.
At the optimum conditions, 81.0% 0f the crude oil was removed with 1.5% APG1214 solution, while the crude oil removal efficiency of the deionized water was only 30.1%; the addition of inorganic salts further improved the removal efficiency to 97.4%, and the BET surface area of the soil increased from 0.79 to 4.16 m2g-1. An interesting result was got when analyzing the n-hexane extracts of the washed soil samples with GC/MS that the APG1214 and the inorganic salts both preferentially removed small n-alkanes in crude oil when they were added individually, however, once they were added together they tended to remove more large n-alkanes. The reason of this phenomenon is still under investigation.
The influence of washing time on crude oil components remaining in soil was also investigated. The results showed that the large n-alkanes (from C24 to C33) to small n-alkanes ( from nC16 to nC23) ratio (abundance) decreased as the washing time increased from 1 to 30 min; and after 30 min the ratio of small n-alkanes to large n-alkanes was higher compared to that in the original contaminated soil before washing, which was unexpected. Researches are undergoing to find the reason for this result. The present study confirmed that APG1214, as a green surfactant, shows a bright future in the remediation of weathered crude oil contaminated soil. |
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