SORPTION OF AN ALCOHOL ETHOXYLATE SURFACTANT TO NATURAL SEDIMENTS

Abstract

U.S. consumer and industrial use of surfactants results in down the drain disposal and release after treatment in septic fields or sewage plants. Effluent may contain limited concentrations of surfactant, which may remain in receiving waters, and this residual surfactant could become associated with bottom sediments. To assess this phenomenon, we have examined the sorption of a radiolabeled alcohol ethoxylate (C15 alcohol with an average of 9 moles of ethylene oxide per mole of alcohol) to natural sediments under sterile conditions to assure that the surfactant was not biodegraded. Control experiments comparing sterilized systems with systems including 1% formalin indicated that formalin could be included in the sediment/surfactant/water mixture to prevent surfactant biodegradation yet not interfere in the sorption process. Four sediments with 0.3–2.2% organic carbon content were used in this study to determine the effect of various sediment properties on the sorption process. Equilibrium sorption was established in 2–4 h. The equilibrium sorption isotherms were determined to be nonlinear and described by the Freundlich model, and distribution ratios (ratio of surfactant concentration on sediment to aqueous concentration) at 1 mg/L surfactant ranged from 350 to 2,100 L/kg. The amount of sorption was better correlated to the percent clay content of the sediment than to the percent organic carbon content of the sediment.