Reductive/oxidative sequential bioelectrochemical process for Perchloroethylene (PCE) removal: effect of the applied reductive potential and microbial community characterization

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In this paper, a bioelectrochemical process has been developed by the combination of two membrane-less reactors equipped with an internal graphite granules counterelectrode for the perchloroethylene (PCE) removal through a reductive/oxidative sequence. In the reductive reactor, the cathodic chamber supplied the reducing power to PCE dechlorinating biomass while a rutile electrode promoted the aerobic dechlorination of the less chlorinated PCE byproducts by oxygen in situ evolution. Two potentiostatic conditions, -350 and -550 mV vs SHE, were tested on the reductive reactor, which showed the capability to completely reduce the PCE into vinyl chloride (VC) and ethylene (Eth). These compounds were completely removed by the oxidative reactor with an average VC and Eth removal efficiency of 94 ± 1% and 98 ± 1%. The -350 mV vs SHE condition resulted in the higher coulombic efficiency for the reductive dechlorination which reached 22 ± 7 % while by increasing the reductive potential to -550 mV the coulombic efficiency drop down to 6 ± 1 % in favor of the methanogenesis reaction. Dehalococcoides mccartyi was found at high abundance in the reducing reactor while a heterogeneous bacterial consortium was observed in the oxidative reactor. Microbiome characterization of the reductive and oxidative reactors showed the concomitant presence of different redox niches in each compartment suggesting that the exchange of ionic species between the electrode and the counterelectrode allowed the co-existence of both reducing and oxidative reactions.