Progress Towards Bioelectrochemical Remediation of Hexavalent Chromium

Abstract

Chromium is one of the most frequently used metal contaminants. Its hexavalent form Cr(VI), which is exploited in many industrial activities, is highly toxic, is water-soluble in the full pH range, and is a major threat to groundwater resources. Alongside traditional approaches to Cr(VI) treatment based on physical-chemical methods, technologies exploiting the ability of several microorganisms to reduce toxic and mobile Cr(VI) to the less toxic and stable Cr(III) form have been developed to improve the cost-effectiveness and sustainability of remediating hexavalent chromium-contaminated groundwater. Bioelectrochemical systems (BESs), principally investigated for wastewater treatment, may represent an innovative option for groundwater remediation. By using electrodes as virtually inexhaustible electron donors and acceptors to promote microbial oxidation-reduction reactions, in in situ remediation, BESs may offer the advantage of limited energy and chemicals requirements in comparison to other bioremediation technologies, which rely on external supplies of limiting inorganic nutrients and electron acceptors or donors to ensure proper conditions for microbial activity. Electron transfer is continuously promoted/controlled in terms of current or voltage application between the electrodes, close to which electrochemically active microorganisms are located. Therefore, this enhances the options of process real-time monitoring and control, which are often limited in in situ treatment schemes. This paper reviews research with BESs for treating chromium-contaminated wastewater, by focusing on the perspectives for Cr(VI) bioelectrochemical remediation and open research issues.

Metagenomic Analysis Reveals Microbial Interactions at the Biocathode of a Bioelectrochemical System Capable of Simultaneous Trichloroethylene and Cr(VI) Reduction

“…have been reported ( Horitsu et al, 1987 ; Turick and Apel, 1997 ; Desai et al, 2008 ; Sarangi and Krishnan, 2008 ; Elangovan et al, 2010 ; Beretta et al, 2018 ; Kabir et al, 2018 ). Several studies also demonstrated that indirect Cr(VI) bioreduction is achievable through injections of biodegradable organic substrates that prompt anaerobic conditions and reductant production such as iron and sulfur species capable of mediating Cr(VI) reduction to Cr(III) ( Kim et al, 2001 ; Somenahally et al, 2013 ; Beretta et al, 2018 , 2019 ). Further, under anaerobic conditions, direct Cr(VI) reduction can be mediated by membrane-bound reductases encoded by mtrA , mtrB , mtrC genes, and soluble enzymes (e.g., soluble cytochrome c3; Belchik et al, 2011 ; Thatoi et al, 2014 ).…”

Improved performance of Cr(vi)-reducing microbial fuel cells by nano-FeS hybridized biocathodes

“…First, the cathode EET remains low, especially with Cr( vi ) reduction that produces cathode passivation via nonconductive Cr( iii ) deposition. 13,14 Second, cathodic microbial activity remains low, especially after exposure to high concentrations of Cr( vi ) that releases toxic attack. 3,15…”

“…First, the cathode EET remains low, especially with Cr(VI) reduction that produces cathode passivation via nonconductive Cr(III) deposition. 13,14 Second, cathodic microbial activity remains low, especially aer exposure to high concentrations of Cr(VI) that releases toxic attack. 3,15 Nano-FeS is an environmentally friendly iron-based material with high specic surface area, high reactivity, high electrical conductivity, and good biocompatibility.…”

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

“…Especially, Cr(VI) reduction by microorganisms is being recognized as an eventual treatment. Despite successful outcomes, certain disadvantages such as low efficiency and poor compatibility due to limited availability of electron donors and other inducers often hamper the prominence of Cr(VI) bioremediation in large-scale implementation ( Malaviya and Singh, 2016 ; Beretta et al, 2019 ; Wang et al, 2020 ). These limitations can be subdued by introducing low concentrations of suitable chemicals in the medium ( Figure 1 ).…”