title: Influence of nitrate and sulfate reduction in the bioelectrochemically assisted dechlorination of cis-DCE.
abstract: This paper investigated the reductive dechlorination (RD) of cis-dichloroethylene (cis-DCE) (average influent 14.2±0.7 μM) by a bioelectrochemical system (BES), in the presence of real contaminated groundwater containing high levels of nitrate and sulfate. The BES enhanced both the RD and competing reactions, such as nitrate and sulfate reductions, which occurred with neither an external organic carbon source nor any inoculum other than the indigenous microbial consortia in the real groundwater. In preliminary batch tests, RD and full nitrate removal occurred after a short lag phase, whereas sulfate reduction occurred slowly and alongside the RD. Under continuous flow conditions (hydraulic retention time, HRT, 1.4 d), the competition of different electron acceptors was strongly affected by the cathodic potential in the range -550 to -750 mV vs. standard hydrogen electrode (SHE). Nitrate reduction was driven to completion at all tested cathodic potentials, whereas sulfate reduction and the RD rate increased as the cathodic potential became more negative. At -750 mV vs. SHE, strong methanogenesis was also observed and became the most important sink of electrons. The overall coulombic efficiency decreased while the potential became more negative. The RD contribution was always less than 1%. Hence, greater energy consumption was required to obtain higher RD rate and better conversion. Anodic oxidation was only observed at -750 mV vs. SHE where almost 39% of residual vinyl chloride (VC) was oxidized and the sulfate was formed back from sulfide (further contributing to electric waste).
authors.affiliation: Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Agnese
authors.initials: A
authors.lastname: Lai
authors.affiliation: Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy. Electronic address: roberta.verdini@uniroma1.it.
authors.forename: Roberta
authors.initials: R
authors.lastname: Verdini
authors.affiliation: Water Research Institute (IRSA-CNR), National Research Council, 00016 Monterotondo, RM, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Aulenta
authors.affiliation: Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Majone
mesh_terms: D001673:Biodegradation, Environmental; D004000:Dichloroethylenes / Q000378:metabolism*; D055664:Electrochemical Techniques / Q000379:methods; D060587:Groundwater / Q000737:chemistry*; D054879:Halogenation; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D013431:Sulfates / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000378:metabolism*; D018508:Water Purification / Q000379:methods*
chemical_list: D004000:Dichloroethylenes; D009566:Nitrates; D013431:Sulfates; D014874:Water Pollutants, Chemical
keywords: Bioelectrochemical remediation; Chlorinated solvents; Groundwater; Reductive dechlorination