Abstract
Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to their improper use in several industrial activities. Specialized microorganisms are able to perform the reductive dechlorination (RD) of high-chlorinated CAHs such as perchloroethylene (PCE), while the low-chlorinated ethenes such as vinyl chloride (VC) are more susceptible to oxidative mechanisms performed by aerobic dechlorinating microorganisms. Bioelectrochemical systems can be used as an effective strategy for the stimulation of both anaerobic and aerobic microbial dechlorination, i.e., a biocathode can be used as an electron donor to perform the RD, while a bioanode can provide the oxygen necessary for the aerobic dechlorination reaction. In this study, a sequential bioelectrochemical process constituted by two membrane-less microbial electrolysis cells connected in series has been, for the first time, operated with synthetic groundwater, also containing sulphate and nitrate, to simulate more realistic process conditions due to the possible establishment of competitive processes for the reducing power, with respect to previous research made with a PCE-contaminated mineral medium (with neither sulphate nor nitrate). The shift from mineral medium to synthetic groundwater showed the establishment of sulphate and nitrate reduction and caused the temporary decrease of the PCE removal efficiency from 100% to 85%. The analysis of the RD biomarkers (i.e., Dehalococcoides mccartyi 16S rRNA and tceA, bvcA, vcrA genes) confirmed the decrement of reductive dechlorination performances after the introduction of the synthetic groundwater, also characterized by a lower ionic strength and nutrients content. On the other hand, the system self-adapted the flowing current to the increased demand for the sulphate and nitrate reduction, so that reducing power was not in defect for the RD, although RD coulombic efficiency was less.
Highlights
Chlorinated aliphatic hydrocarbons (CAHs), such as perchloroethylene (PCE) and trichloroethylene (TCE), are organic molecules in which chlorine atoms are directly linked to the carbon skeleton
PCE dechlorination products detected in reductive reactor effluent were predominantly vinyl chloride (VC) ethylene (Eth) and ethane (Eta), i.e., no high-chlorinated byproducts were detected in the reductive reactor effluent (Figure 2b)
The shift of the feeding solution from a well-balanced mineral medium to a simpler synthetic groundwater caused a temporary inhibition of the PCE removal efficiency, which dropped down from 99 ± 1 to 85 ± 2%
Summary
Chlorinated aliphatic hydrocarbons (CAHs), such as perchloroethylene (PCE) and trichloroethylene (TCE), are organic molecules in which chlorine atoms are directly linked to the carbon skeleton. Due to the peculiar chemical and physical proprieties, the CAHs were widely utilized in many industrial activities (e.g., dry cleaning devices, degreasing in the heavy industries) [1]. Due to their large use coupled with past uncontrolled handling and disposal, CAHs became ubiquitous contaminants in groundwater, soils, and sediments [2]. Each RD step consumes two electrons and provokes the substitution of a chlorine with a hydrogen to the ethene skeleton, i.e., four reductive steps (eight electrons) are required to convert PCE to ethylene (Eth). D. mccartyi activity is driven by strain-specific enzymes coded by reductive dehalogenase genes, including tceA, bvcA, and vcrA [5,6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
