Phase distribution of hexachlorobenzene in a suspended-growth culture amended with a polysorbate surfactant.

The effect of a non-ionic surfactant on the phase distribution of hexachlorobenzene (HCB) in a suspended-growth culture system was assessed. Tween 60, a polyoxyethylene sorbitan stearate ester surfactant, and an azide-inactivated, mixed, methanogenic, HCB-dechlorinating culture were used in this work. The sorption of HCB on the biomass as well as sorption and aggregation/precipitation of Tween 60 were experimentally quantified. The values of the HCB and Tween 60 distribution parameters were determined and the phase distribution of HCB in the presence of surfactant and biomass was described quantitatively. Both the HCB and surfactant distribution are highly dependent on the total amount of surfactant present in the system. At low initial surfactant concentrations, most of the HCB is associated with the biomass. As the surfactant concentration increases, the effect of surfactant sorption and precipitation diminishes and the higher pool of surfactant micelles shifts the distribution of HCB from the solid phase to the solution phase. The HCB phase distribution in the presence of the surfactant may have a significant effect on HCB bioavailability for reductive dechlorination. The quantitative description of the HCB phase distribution presented here was subsequently used as the basis for the development of a model that describes the bioavailability and reductive dechlorination of HCB in a surfactant/biomass system.