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
Abstract:Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of di… Show more
“…Metagenomic studies have been previously conducted on stable dechlorinating consortia to shed light on the metabolic features of the microbial components and their role in the RD processes under different conditions ( Brisson et al, 2012 ; Maphosa et al, 2012 ; Dam et al, 2017 ; Wang et al, 2019 ; Kucharzyk et al, 2020 ). Similarly, some metagenomic studies have also been conducted on biological systems for Cr(VI) removal to explore the metabolic potential, including Cr(VI) remediation genes, primarily in wastewater treatment systems or microbial consortia ( Miao et al, 2015 ; Sun et al, 2019 ; Pei et al, 2020 ; Rahman and Thomas, 2021 ). To the best of our knowledge, no metagenomic studies have been conducted on a bioelectrochemical system for simultaneous TCE/Cr(VI) reduction.…”
Bioelectrochemical systems (BES) are attractive and versatile options for the bioremediation of organic or inorganic pollutants, including trichloroethylene (TCE) and Cr(VI), often found as co-contaminants in the environment. The elucidation of the microbial players’ role in the bioelectroremediation processes for treating multicontaminated groundwater is still a research need that attracts scientific interest. In this study, 16S rRNA gene amplicon sequencing and whole shotgun metagenomics revealed the leading microbial players and the primary metabolic interactions occurring in the biofilm growing at the biocathode where TCE reductive dechlorination (RD), hydrogenotrophic methanogenesis, and Cr(VI) reduction occurred. The presence of Cr(VI) did not negatively affect the TCE degradation, as evidenced by the RD rates estimated during the reactor operation with TCE (111±2 μeq/Ld) and TCE/Cr(VI) (146±2 μeq/Ld). Accordingly, Dehalococcoides mccartyi, the primary biomarker of the RD process, was found on the biocathode treating both TCE (7.82E+04±2.9E+04 16S rRNA gene copies g−1 graphite) and TCE/Cr(VI) (3.2E+07±2.37E+0716S rRNA gene copies g−1 graphite) contamination. The metagenomic analysis revealed a selected microbial consortium on the TCE/Cr(VI) biocathode. D. mccartyi was the sole dechlorinating microbe with H2 uptake as the only electron supply mechanism, suggesting that electroactivity is not a property of this microorganism. Methanobrevibacter arboriphilus and Methanobacterium formicicum also colonized the biocathode as H2 consumers for the CH4 production and cofactor suppliers for D. mccartyi cobalamin biosynthesis. Interestingly, M. formicicum also harbors gene complexes involved in the Cr(VI) reduction through extracellular and intracellular mechanisms.
“…Metagenomic studies have been previously conducted on stable dechlorinating consortia to shed light on the metabolic features of the microbial components and their role in the RD processes under different conditions ( Brisson et al, 2012 ; Maphosa et al, 2012 ; Dam et al, 2017 ; Wang et al, 2019 ; Kucharzyk et al, 2020 ). Similarly, some metagenomic studies have also been conducted on biological systems for Cr(VI) removal to explore the metabolic potential, including Cr(VI) remediation genes, primarily in wastewater treatment systems or microbial consortia ( Miao et al, 2015 ; Sun et al, 2019 ; Pei et al, 2020 ; Rahman and Thomas, 2021 ). To the best of our knowledge, no metagenomic studies have been conducted on a bioelectrochemical system for simultaneous TCE/Cr(VI) reduction.…”
Bioelectrochemical systems (BES) are attractive and versatile options for the bioremediation of organic or inorganic pollutants, including trichloroethylene (TCE) and Cr(VI), often found as co-contaminants in the environment. The elucidation of the microbial players’ role in the bioelectroremediation processes for treating multicontaminated groundwater is still a research need that attracts scientific interest. In this study, 16S rRNA gene amplicon sequencing and whole shotgun metagenomics revealed the leading microbial players and the primary metabolic interactions occurring in the biofilm growing at the biocathode where TCE reductive dechlorination (RD), hydrogenotrophic methanogenesis, and Cr(VI) reduction occurred. The presence of Cr(VI) did not negatively affect the TCE degradation, as evidenced by the RD rates estimated during the reactor operation with TCE (111±2 μeq/Ld) and TCE/Cr(VI) (146±2 μeq/Ld). Accordingly, Dehalococcoides mccartyi, the primary biomarker of the RD process, was found on the biocathode treating both TCE (7.82E+04±2.9E+04 16S rRNA gene copies g−1 graphite) and TCE/Cr(VI) (3.2E+07±2.37E+0716S rRNA gene copies g−1 graphite) contamination. The metagenomic analysis revealed a selected microbial consortium on the TCE/Cr(VI) biocathode. D. mccartyi was the sole dechlorinating microbe with H2 uptake as the only electron supply mechanism, suggesting that electroactivity is not a property of this microorganism. Methanobrevibacter arboriphilus and Methanobacterium formicicum also colonized the biocathode as H2 consumers for the CH4 production and cofactor suppliers for D. mccartyi cobalamin biosynthesis. Interestingly, M. formicicum also harbors gene complexes involved in the Cr(VI) reduction through extracellular and intracellular mechanisms.
“…Under anaerobic conditions, several types of organic substrates have been reported to be able to reduce hexavalent chromium successfully, such as glucose, lactate, sucrose, milk whey, etc. [13]. Within the context of this study, molasses emulsified vegetable oil (EVO) and ferrous sulfate heptahydrate (FeSO 4 •7H 2 O) were used as electron donors, independently and as combinations.…”
Section: Microcosms Designmentioning
confidence: 99%
“…Microbial remediated Cr(VI) reduction can occur under both aerobic and anaerobic conditions and is mediated by a variety of enzymes, being cited extracellularly, intracellularly, or in the cytoplasmic membrane [13,14]. A reduction can also be induced by metabolic byproducts, such as bio-generated Fe(II), hydrogen, and/or sulfides [15][16][17].…”
Increased groundwater and soil contamination by hexavalent chromium have led to the employment of a variety of detoxification methods. Biological remediation of Cr(VI) polluted aquifers is an eco-friendly method that can be performed in situ by stimulating the indigenous microbial population with organic and inorganic electron donors. In order to study the effect of different redox conditions on microbial remediated Cr(VI) reduction to Cr(III), microcosm experiments were conducted under anaerobic, anoxic, and sulfate-reducing conditions and at hexavalent chromium groundwater concentrations in the 0–3000 μg/L range, with groundwater and soil collected from an industrial area (Inofyta region). As electron donors, molasses, emulsified vegetable oil (EVO), and FeSO4 were employed. To quantitatively describe the degradation kinetics of Cr(VI), pseudo-first-order kinetics were adopted. The results indicate that an anaerobic system dosed with simple or complex external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III), while the addition of Fe2+ can further increase Cr(VI) removal rate significantly. Furthermore, Cr(VI) microbial reduction is possible in the presence of NO3− at rates comparable to anaerobic Cr(VI) microbial reduction, while high sulfate concentrations have a negative effect on Cr(VI) bioreduction rates in comparison to lower sulfate concentrations.
“…Figure 5 depicts the intracellular and extracellular mitigation pathways for Cr (VI) by microalgae. Figure 5 Proposed biotransformation pathways of Cr(VI) developed from the finding of ( Deng et al., 2006 ; Lee et al., 2017 ; Rahman and Thomas, 2021 ; Yen et al., 2017 ). …”
Section: Mechanisms Of Hms Phycoremediation Using Living Microalgaementioning
confidence: 99%
“… Proposed biotransformation pathways of Cr(VI) developed from the finding of ( Deng et al., 2006 ; Lee et al., 2017 ; Rahman and Thomas, 2021 ; Yen et al., 2017 ). …”
Section: Mechanisms Of Hms Phycoremediation Using Living Microalgaementioning
Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.
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