PHASE DISTRIBUTION OF HEXACHLOROBENZENE IN A SUSPENDED-GROWTH CULTURE AMENDED WITH A POLYSORBATE SURFACTANT

The effect of a nonionic 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 and HCB-dechlorinating culture were used in this work. The sorption of HCB on the biomass, sorption and aggregation/precipitation of Tween 60, as well the HCB solubilization capacity of Tween 60 were experimentally assessed. 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 is 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- 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 can be used for the development of a model, which describes the bioavailability and reductive dechlorination of HCB in a surfactant/biomass system.