Relationship between PCB desorption equilibrium, kinetics, and availability during land biotreatment

The purpose of this research was to study the changes in polychlorinated biphenyl (PCB) availability as measured by desorption equilibrium and kinetics from industrial lagoon sediments collected at different times during a 24-month period of pilot-scale land biotreatment. During biotreatment, reductions of the lower chlorinated PCB congeners in the industrial lagoon sediments were observed. On the basis of past work on soils and sediments, it was originally hypothesized that these reductions in PCB concentration would result in reduced PCB availability. To evaluate this hypothesis, equilibrium partitioning studies and desorption kinetic studies were conducted with the industrial lagoon sediments (containing 0.91% oil and grease) as a function of biotreatment duration. Contrary to initial expectations, equilibrium aqueous total PCB concentrations increased with PCB loss during land biotreatment. This behavior was attributed to the association of PCBs with a waste oil phase in the lagoon sediment and an oil phase loss rate greater than the PCB loss rate during the biodegradation study. Maximum PCB desorption rates for the lagoon sediments also changed with biotreatment. A two-phase desorption behavior characterized by fast and slow desorbing fractions were observed. The estimated fast pool fraction for each PCB homologue decreased with biotreatment time, suggesting preferential removal of the PCBs from the fast pool during the bioremediation process. Although PCB availability based on estimated fast pool fraction decreased with biotreatment, availability based on aqueous equilibrium measurements increased with biotreatment over the 24 months of study.