Experimental investigation of the removal of hydrophobic organic compounds from two Iowa soils using food grade surfactants and recovery of used surfactants

Abstract

The ability of food grade aqueous surfactant solutions to remove toluene or 1,2,4-trichlorobenzene entrapped in sand and two Iowa soils was evaluated in batch and column experiments. Also, the effects that environmental conditions have on contaminant solubilization and mobilization by surfactants and the technical viability of recovering the surfactants for possible reuse were studied. Synergism between the anionic Dowfax 8390 and the nonionic T-Maz 60 was not observed. A mixture of the two was less effective than Dowfax 8390 by itself. 1,2,4-trichloroben2ene removal enhancements via microemulsifiers were less effective than that by Dowfax 8390 for a sandy soil. Food grade surfactants were suitable for surfactant-aided remediation of Fruitfield Iowa soils contaminated with toluene or 1,2,4-trichlorobenzene. Based on the experimental results, optimal range for each environmental parameters was: 1) Surfactant solution pH: 10, 2) Surfactant solution concentration; 4%(v/v), 3) Surfactant solution average temperature: 33.4°C, 4) Surfactant solution flow rate: 4mL/min, 5) Surfactant solution volume to soil weight ratio: 4. The removal of 95% of 1,2,4-trichlorobenzene was obtained with optimal conditions. In addition, surfactant-assisted saturated hydraulic conductivity losses were observed experimentally and should be considered prior to in-situ surfactant remediation. Counter-current solvent extraction was investigated to determine its efficiency for used surfactant recovering. A simple counter-current extraction apparatus with a convex orifice system was used. Hexane, acetone, and methylene chloride were used as the counter-current solvent. Toluene was effectively removed from the anionic surfactant solution using methylene chloride solvent and 1,2,4trichlorobenzene was effectively removed from the anionic surfactant solution using hexane or methylene chloride. Removal of toluene was greatest at 30ml-/min of methylene chloride flow rate and 1,2,4-trichlorobenzene was greatest at 10mL/min of hexane flow rate. This study suggests that counter-current solvent extraction methods may help to recycle anionic surfactant solutions used for remediation of contaminated soil and groundwater.