Evaluation of Acetate Thresholds Under Various Terminal Electron-Accepting Conditions: Application to Bioremediation Monitoring

Abstract

A major challenge associated with intrinsic bioremediation is demonstrating its success. The consumption of electron acceptors during bioremediation of hydrocarbons and other contaminants can result in shifts in the predominant terminal electron-accepting processes (TEAPs), which may be useful for monitoring. Because traditional assessment tools have disadvantages, an accurate indicator of TEAPs is still needed. Acetate thresholds were evaluated to test the hypothesis that characteristic ranges of acetate thresholds may exist for different TEAPs and be useful as a bioremediation monitoring tool. Acetate thresholds established by pure microbial batch cultures using different TEAPs were measured experimentally. Furthermore, the factors controlling acetate thresholds were investigated using a microbial respiration model. Acetate thresholds increased in the order: Fe(III)<Mn(IV)=nitrate<sulfate<CO2. Modeling results indicated that acetate thresholds were controlled by kinetics under Mn(IV)-, nitrate- and sulfate-reducing conditions and by thermodynamics under methanogenic conditions. The results suggested that acetate thresholds could be a potentially useful bioremediation indicator.