Microbial Assisted Hexavalent Chromium Removal in Bioelectrochemical Systems

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.

Effect of hydraulic retention time on the electro-bioremediation of nitrate in saline groundwater

“…Most of the studies focus on the removal of one type of contaminant at a time (e.g., nitrate, organics, heavy metals, calcium, etc. ), which is useful for a deep understanding and optimisation of the processes involved (Beretta et al, 2020;Ceballos-Escalera et al, 2022Palma et al, 2018;Sevda et al, 2018;Verdini et al, 2015). However, groundwater matrices are highly complex and heterogeneous, influencing the behaviour of BES and representing a key aspect of process development and scale-up.…”

Cu(II) and Cr(VI) Removal in Tandem with Electricity Generation via Dual-Chamber Microbial Fuel Cells

“…Cu(II) gains one electron to produce Cu(I) (Cu 2 O), which then gains another electron to produce elemental copper [29]. In contrast, at pH > 2, Cr(VI) can directly gain electrons for reduction to Cr(III) in terms of Cr(OH) 3 or Cr 2 O 3 precipitated on the cathode electrode [31,34]. In this study, the weight percentage of chromium on the stainless steel increased from 19.04% to 24.34% as the chromium concentration increased from 10 to 150 mg/L, while that on the titanium sheet and graphite plate were even higher at 38.95% and 30.47% when the chromium concentration was 100 mg/L.…”

<em>In situ</em> Groundwater Treatment with Bioelectrochemical Systems (BES): Critical Review and Future Perspectives

“…A flow-through setup, similar to the one descripted by Pous et al (2017), may represent an option: in this case the contaminated stream would first be exposed to the anode, allowing oxidation processes, and then to the cathode where reduction would occur. Another option is the use of anocathodophilic bacteria that employ electrodes as both electron acceptors and donors based on redox conditions; some examples have been reported for biofilms capable of catalyzing organic matter oxidation and NO3or chromium reduction (Beretta et al, 2018;Molognoni et al, 2017;Pous et al, 2016).…”