Bioelectrochemical Chlorinated Aliphatic Hydrocarbons Reduction in Synthetic and Real Contaminated Groundwaters

Abstract

The widespread contamination of chlorinated aliphatic hydrocarbons (CAHs) as Perchloroethylene (PCE) and Trichloroethylene (TCE) over the past recent years and their uncorrected disposal and storing brought these substances to become one of the most common contaminants of subsoils and groundwater in the world. In recent years, more sustainable remediation and cost-effective technologies involving groundwater’s indigenous microorganism such as the dehalorespiring microorganisms. Dehalorespiring microorganisms can reduce PCE and TCE via reductive dechlorination (RD) while aerobic dechlorinating microorganisms oxidized low chlorinated compound such as cis-dichloroethylene (cDCE) and vinyl chloride (VC) into non harmful products. The integration of reductive dechlorination and aerobic dechlorination results in an efficient approach for the complete mineralization of high chlorinated compounds, which usually led to a build-up of VC. Bioelectrochemical systems, which exploit the capability of microorganisms to interact with a polarized electrode, provide an effective strategy to promote reductive and oxidative environments by the regulation of the applied potentials. Indeed, the complete mineralization of high chlorinated CAHs, can be obtained by a sequential reductive/oxidative bioelectrochemical process which allows for the optimization of the reductive and oxidative dechlorinating conditions. In this study the performances of the reductive reactor, devoted to the reductive dechlorination has been presented with three different contaminated feeding solutions. The three different feeding solutions included an optimized mineral medium, a synthetic groundwater (constituted by tap water added with nitrate and sulphate) and a real contaminated groundwater. Moreover, different operating conditions like hydraulic retention time (HRT) and applied cathodic potential have been investigated to assess the performance of the reductive dechlorination and on side reactions. The analysis of the coulombic efficiencies for the reductive dechlorination in the reductive reactor showed an important effect of the feeding solution composition and operating conditions (applied potential and HRT), namely strongly decreasing under when using real contaminated groundwater. Despite the progressive decrease of the coulombic efficiency obtained using more complex matrixes, the CAHs removal rates along with the energetic consumption of the process showed an advantageous perspective in the adoption of the bioelectrochemical process for the stimulation of the reductive dechlorination reaction.