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.
Highlights
Hexavalent Cr(VI) and trivalent Cr(III) chromium are the most common forms of this element in the environment
The pump and treat (P&T) method, which involves the extraction of contaminated water from the aquifer and above-ground treatment, tends to be poorly efficient when dealing with contaminated plumes at relatively low Cr(VI) concentrations [17]
This review provides a comprehensive analysis of the current knowledge and experiences in bio-electrochemical treatment of Cr(VI) contaminated water streams, in order to explore bioelectrochemical systems (BESs) opportunities for in situ groundwater bioremediation
Summary
Hexavalent Cr(VI) and trivalent Cr(III) chromium are the most common forms of this element in the environment. Hexavalent chromium in industrial wastewater is typically treated by reduction, and subsequent precipitation, to the non-toxic Cr(III) by means of reductants (for instance, FeSO4 , Na2 S2 O5 , and SO2 ) [11] or electrochemical processes (including electrocoagulation, electro-reduction, electrodialysis, and electro-deionization) [12] These processes are easy to implement and efficient at high or moderate Cr(VI) concentrations. The use of reductants produces a large amount of metallic sludge, and both the above-mentioned approaches are either ineffective or not cost-effective when applied for trace Cr(VI) treatment Adsorption on adsorbents, such as activated carbons or zeolites, is adopted, since this process exhibits several advantages of simple operation, low cost, and high efficiency [13,14].
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