Use of benzoate to establish reactive buffer zones for enhanced attenuation of BTX migration: Aquifer column experiments

Flow-through aquifer columns were used to evaluate the efficacy of using benzoate as a biostimulatory substrate to enhance the aerobic biodegradation of benzene, toluene, and o-xylene (BTX), fed continuously at low concentrations (about 0.2 mg/L each). When used as a cosubstrate, benzoate addition (1 mg/L) enhanced BTX degradation kinetics and attenuated BTX breakthrough relative to acetate-amended (2 mg/L) or unamended control columns. The benzoate-amended column also experienced an increase in predominance of pseudomonad species capable of degrading BTX. The feasibility of injecting benzoate to enhance the growth of BTX degraders and establish a buffer zone downgradient of a BTX plume was also investigated. Using pristine aquifer material without previous exposure to BTX, aquifer columns were fed benzoate (2 mg/L), acetate (4 mg/L), or mineral medium without supplemental substrates during a 2-day acclimation stage. All columns were subsequently fed BTX alone, and their breakthrough was monitored. Previous exposure to benzoate, but not to acetate, shortened the acclimation period to BTX degradation and enhanced the short-term bioattenuation potential of the indigenous consortium. This suggests that benzoate could potentially be used to establish and sustain in situ reactive zones to attenuate BTX migration and protect downgradient groundwater resources.