PROPERTIES OF FOOD GRADE (EDIBLE) SURFACTANTS AFFECTING SUBSURFACE REMEDIATION OF CHLORINATED SOLVENTS

In this research, several food grade (edible) surfactants are systemat ically evaluated for various loss mechanisms: precipitation, adsorptio n, and coacervation (for nonionic surfactants). Cloud points for the p olyethoxylate sorbitan (T-MAZ) surfactants are much higher than aquife r temperatures, and the effects on surfactant losses should be minimum . Precipitation boundaries of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium mono- and dimethylnaphthalene sulfonate (SMDNS) were established. Existing precipitation models successfully predicted prec ipitation boundaries for SMDNS but showed minor deviations for AOT res ults. AOT was more susceptible to precipitation than the cosurfactant evaluated, SMDNS. Nonionic polyethoxylate (POE = 20) sorbitan monostea rate (T-MAZ-60) and POE(80) sorbitan monolaurate (T-MAZ-28) formed liq uid crystal phases at high surfactant concentrations (> 0.5 wt %) whit e POE(20) sorbitan monolaurate (T-MAZ-20) and POE(20) sorbitan monoole ate (T-MAZ-80) remained in aqueous solution at concentrations up to 5 wt %. T-MAZ-60 and T-MAZ-28 also showed a continuous increase of ''ads orption'' at high surfactant concentrations (likely due to liquid crys tal formation). Other surfactants showed Langmuirian-shaped isotherms at high concentration, while the cosurfactant SMDNS experienced neglig ible adsorption. On a mass basis, the maximum adsorption (q(max) in mu mol/g) was higher for T-MAZ surfactants than for alkylphenol ethoxyla tes, AOT, and disulfonated surfactants.