Abstract
Groundwater is the environmental matrix that is most frequently affected by anthropogenic hexavalent chromium contamination. Due to its carcinogenicity, Cr(VI) has to be removed, using environmental-friendly and economically sustainable remediation technologies. BioElectrochemical Systems (BESs), applied to bioremediation, thereby offering a promising alternative to traditional bioremediation techniques, without affecting the natural groundwater conditions. Some bacterial families are capable of oxidizing and/or reducing a solid electrode obtaining an energetic advantage for their own growth. In the present study, we assessed the possibility of stimulating bioelectrochemical reduction of Cr(VI) in a dual-chamber polarized system using an electrode as the sole energy source. To develop an electroactive microbial community three electrodes were, at first, inserted into the anodic compartment of a dual-chamber microbial fuel cell, and inoculated with sludge from an anaerobic digester. After a period of acclimation, one electrode was transferred into a polarized system and it was fixed at −0.3 V (versus standard hydrogen electrode, SHE), to promote the reduction of 1000 µg Cr(VI) L−1. A second electrode, served for the set-up of an open circuit control, operated in parallel. Cr(VI) dissolved concentration was analysed at the initial, during the experiment and final time by spectrophotometric method. Initial and final microbial characterization of the communities enriched in polarized system and open circuit control was performed by 16S rRNA gene sequencing. The bioelectrode set at −0.3 V showed high Cr(VI) removal efficiency (up to 93%) and about 150 µg L−1 day−1 removal rate. Similar efficiency was observed in the open circuit (OC) even at about half rate. Whereas, purely electrochemical reduction, limited to 35%, due to neutral operating conditions. These results suggest that bioelectrochemical Cr(VI) removal by polarized electrode offers a promising new and sustainable approach to the treatment of groundwater Cr(VI) plumes, deserving further research.
Highlights
Extensive use of chromium (Cr) and its compounds in many industrial process [1] and refractory production has made it a major pollutant [2]
Purely electrochemical reduction, limited to 35%, due to neutral operating conditions. These results suggest that bioelectrochemical Cr(VI) removal by polarized electrode offers a promising new and sustainable approach to the treatment of groundwater Cr(VI) plumes, deserving further research
The2 between anolyte and catholyte was achieved by a proton exchange membrane
Summary
Extensive use of chromium (Cr) and its compounds in many industrial process [1] and refractory production has made it a major pollutant [2]. The mobility, bioavailability and toxicity of chromium depend on its oxidation states. Cr(III) is most immobile, less soluble and. Cr(VI) is highly mobile, soluble and bioavailable. Compared with Cr(III), Cr(VI) is extremely toxic (by 100 times) to living organisms and it is internationally recognized as a human carcinogen, mutagen and teratogen. To reduce its impact on human health and the environment, appropriate remedial measures and remediation interventions are needed. The recovery and removal of chromium from wastewater or groundwater is traditionally carried out by adsorption, [3,4], chemical or electrochemical reduction to
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