Reductive/Oxidative Sequential Bioelectrochemical Process for Perchloroethylene Removal

Abstract

An innovative bioelectrochemical reductive/oxidative sequential process was developed and tested on a laboratory scale to obtain the complete mineralization of perchloroethylene (PCE) in a synthetic medium. The sequential bioelectrochemical process consisted of two separate tubular bioelectrochemical reactors that adopted a novel reactor configuration, avoiding the use of an ion exchange membrane to separate the anodic and cathodic chamber and reducing the cost of the reactor. In the reductive reactor, a dechlorinating mixed inoculum received reducing power to perform the reductive dechlorination of perchloroethylene (PCE) through a cathode chamber, while the less chlorinated daughter products were removed in the oxidative reactor, which supported an aerobic dechlorinating culture through in situ electrochemical oxygen evolution. Preliminary fluid dynamics and electrochemical tests were performed to characterize both the reductive and oxidative reactors, which were electrically independent of each other, with each having its own counterelectrode. The first continuous-flow potentiostatic run with the reductive reactor (polarized at −450 mV vs SHE) resulted in obtaining 100% ± 1% removal efficiency of the influent PCE, while the oxidative reactor (polarized at +1.4 V vs SHE) oxidized the vinyl chloride and ethylene from the reductive reactor, with removal efficiencies of 100% ± 2% and 92% ± 1%, respectively.

Effects of the Feeding Solution Composition on a Reductive/Oxidative Sequential Bioelectrochemical Process for Perchloroethylene Removal

“…The working electrode of the reductive reactor was also constituted by graphite granules, while in the oxidative reactor, the working electrode was a commercial mixed metal oxides (MMO) electrode (Magneto Special Anodes, The Netherland). The mineral medium solution utilized as feeding solution in the first operational period was the same as previously reported [23]. The synthetic groundwater feeding solution consisted of a tap water solution whose composition is reported in Table 1.…”

“…The reductive reactor was polarized with the cathode (i.e., the working electrode) at −450 mV vs. standard hydrogen electrode (SHE), while the oxidative reactor anode was polarized at +1.4 V vs. SHE. The mineral medium solution utilized as feeding solution in the first operational period was the same as previously reported [23]. The synthetic groundwater feeding solution consisted of a tap water solution whose composition is reported in Table 1.…”

“…As a further advancement, a new configuration was recently proposed where the system was split into two membrane-less independent reactors, respectively, for reductive and oxidative reaction, each one having its own counter electrode. This approach makes it possible to independently tune electrical conditions for each reaction, and the absence of separation membrane makes reactor realization simpler and cheaper, especially in a scaling-up perspective [23,24].…”

“…In this experimental study, the PCE-contaminated feeding solution used for the investigation of the latter process has been shifted from the previously investigated [23,25] mineral medium to a synthetic groundwater. The main novelty here is that the synthetic groundwater was designed based on the anion content of a real contaminated groundwater, i.e., containing sulphate and nitrate species that can introduce competitive processes for the reducing power [25].…”

Ammonium Recovery and Biogas Upgrading in a Tubular Micro-Pilot Microbial Electrolysis Cell (MEC)

“…The electron exchange between the electroactive biofilm and the electrodic material can be directly performed by specialized membrane proteins or by the utilization of mediators, which have the function of electrons shuttles between the biofilm and the electrode surface [22,23]. Biocathode utilization has been investigated for several environmental applications, which includes biofuel production [24,25], CO 2 fixation into VFA (Volatile Fatty Acid) [26,27], and groundwater bioremediation [28,29]. The bioelectrochemical reduction of CO 2 into CH 4 , named the bioelectromethanogenesis reaction, is obtained by using an electrodic material for the reducing power supply to mixed methanogenic consortium, which adopts the electrodic material as an electron donor.…”