Relative contribution of set cathode potential and external mass transport on TCE dechlorination in a continuous-flow bioelectrochemical reactor

• A continuous flow bioelectrochemical system is used for bioremediation of chlorinated solvents.
• Both the flow-rate and the cathodic potential influence the reductive dechlorination (RD) rate.
• The RD rate increases at higher flow rate but conversion yield decreases.
• Mass transport phenomena influence the rate of RD at more reductive potential (−450 mV vs. SHE).
• At −250 mV the dechlorination rate was driven by direct extracellular electron transfer.

Microbial bioelectrochemical systems, which use solid-state cathodes to drive the reductive degradation of contaminants such as the chlorinated hydrocarbons, are recently attracting considerable attention for bioremediation applications. So far, most of the published research has focused on analyzing the influence of key (bio)electrochemical factors influencing contaminant degradation, such as the cathode potential, whereas only few studies have examined the potential impact of mass transport phenomena on process performance. Here we analyzed the performance of a flow-through bioelectrochemical reactor, continuously fed with a synthetic groundwater containing trichloroethene at three different linear fluid velocities (from 0.3 m d−1 to 1.7 m d−1) and three different set cathode potentials (from −250 mV to −450 mV vs. the standard hydrogen electrode). The obtained results demonstrated that, in the range of fluid velocities which are characteristics for natural groundwater systems, mass transport phenomena may strongly influence the rate and extent of reductive dechlorination. Nonetheless, the relative importance of mass transport largely depends on the applied cathode potential which, in turn, controls the intrinsic kinetics of biological reactions and the underlying electron transfer mechanisms.