Optimization of phenanthrene contaminated soil washing using Response Surface Methodology

Background and Aims: Soil washing using surfactant is a promising technology for PAHs removal from soil transferring them into liquid phase. The performance of this process is influenced by several factors such as surfactant concentration, washing time, liquid:soil ratio (L/S) and the presence of natural organic matter, which in the present study was totally investigated using the nonionic surfactant Tween 80.Materials and Methods: Surfactant solution with three various concentrations of 500, 2750, 5000 mg/l, at liquid:soil ratios of 10, 20, 30 v/w (ml/g) containing three concentrations of 0, 10, 20 mg/l humic acid (asNOM) was added to phenanthrene contaminated soil samples. The samples were placed on a shaker for timeinterval of 2, 13 and 24 hours, then it was injected to HPLC for phenanthrene concentration analyze. This research was conducted on the basis of central composite design by using response surface method (RSM) in 29 experimental runs.Results: Maximum removal efficiency (77.35%) was achieved under the experimental conditions of 5000 mg/l surfactant concentration, 30 v/w liquid:soil ratio, absence of humic acid and 24 h washing time. Surfactant concentration with impact value of 82.03% was the most effective parameter in phenanthrene removal. L/S was also the other significant factor (P<0.0001), but humic acid and washing time were, statistically,insignificant. The interaction between surfactant concentration and L/S was significant too.Conclusion: Considering the conditions of Iran’s soils containing 3-6 percent organic matter and based on the suggestions of RSM with 95.10% desirability, the optimum conditions for washing high- phenanthrene soil (about 500 mg/kg) with minimum washing time of 2 hours were as 5000 mg/l surfactant concentration, 30 v/w (ml/g) liquid:soil ratio, and 2.1 mg/l humic acid concentration (6.30%).Key words: phenanthrene, soil washing, surfactant Tween 80, optimizatio