Bioreduction Of Hexavalent Chromium Research Articles

Phosphomolybdic acid enhancing hexavalent chromium bio-reduction in long-term operation: Optimal dosage and mechanism analysis

The bio-reduction of Cr(VI) is regarded as a feasible and safe strategy to treat Cr pollution. The optimal concentration of phosphomolybdic acid (PMo12) for Cr(VI) reduction and the catalytic mechanism of electron behavior (electron production, electron transport and electron consumption) were revealed in denitrifying biofilm systems. The results showed that 0.1 mM PMo12 could achieve 92.5 % removal efficiency of 90 mg/L Cr(VI), which was 47.7 % higher than that of PMo12-free system, and improve the extracellular fixation capacity of Cr(III). The activity of peroxidase (POD) was significantly promoted by PMo12 to repair oxidative stress damage caused by Cr(VI) reduction. Additionally, analysis of electron behavior demonstrated that PMo12 could enhance key indicators of electron production, transport and consumption. This led to rapid activation of the electron pathway inhibited by Cr(VI), enabling simultaneous efficient nitrogen removal and Cr(VI) reduction in the biofilm system. This discovery will provide an efficient technique for Cr-containing wastewater treatment.

Hexavalent chromium bioreduction by chromium-resistant sporulating bacteria isolated from tannery effluent

The main polluting source of heavy metal contamination of water is the leather tanning industry, which uses chrome powder and discharges it into the nearby ecosystem. In this investigation, chromium-resistant bacterial strains were isolated and characterized from tannery effluent. Based on morphological and biochemical characterization, the predominant sporulating Bacillus sp. was isolated and identified as Bacillus subtilis based on 16S rRNA gene sequencing. Chromium degradation by the bacterial strain was evaluated using the flask culture method at three different concentrations (300, 600, and 900 µg/ml) of Cr (VI), and the reduction potential of the isolated bacterium was analyzed by Atomic Absorption Spectrophotometry. A maximum reduction of approximately 78% was found at 24 hrs of incubation at pH 7 and at a constant temperature of 30°C. More than 50% of the Cr(VI) was decreased in 24 hours when the Cr(VI) concentration varied from 300 to 900 g/ml. FTIR analysis showed the involvement of hydroxyl and amine groups in chromium adsorption. As an outcome, this strain could be a promising bioagent for the environmentally friendly elimination of toxic Cr(VI) from polluted environments.

Bioreduction of hexavalent chromium via Bacillus subtilis SL-44 enhanced by humic acid: An effective strategy for detoxification and immobilization of chromium

As an organic macromolecule, humic acid (HA) has been extensively used as the protectant for bacteria applied in Cr(VI) microbial remediation. However, the effect of the structural properties of HA on the reduction rate of bacteria and the respective contribution of bacteria and HA to soil Cr(VI) management remained uncertain. In this paper, the structural differences between two kinds of humic acid (AL-HA and MA-HA) were explored by means of spectroscopy and electrochemical characterization, and the potential influence of MA-HA on Cr(VI) reduction rate and physiological characteristics of bacteria (Bacillus subtilis, SL-44) also were analyzed. The results showed that the phenolic groups and carboxyl on the surface of HA are firstly complex with Cr(VI) ions, and the fluorescent component with more п-п conjugate structure in HA is the most sensitive species. Compared with single bacteria, the application of SL-44 and MA-HA complex (SL-MA) not only enhanced the reduction of 100 mg/L Cr(VI) to 39.8 % within 72 h and formation rate of intermediate Cr(V), but also reduced the electrochemical impedance. Moreover, the addition of 300 mg/L MA-HA also relieved the Cr(VI) toxicity and decreased the accumulation of glutathione to 94.51 % in bacterial extracellular polymeric substance, furthermore down-regulated the gene expression related to amino acid metabolism and polyhydroxybutyric acid (PHB) hydrolysis in SL-44. Finally, the application of SL-MA also enhanced the stability of chromium in soil and decreased its phytoavailability to 86.09 %, which further reduced chromium enrichment in cabbage organs. These findings provide new insights into Cr(VI) removal, which is also critical for evaluating the application potential of HA for enhancing Cr(VI) bio-reduction.

Enhancement of hexavalent chromium reduction by Shewanella oneidensis MR-1 in presence of copper nanoparticles via stimulating bacterial extracellular electron transfer and environmental adaptability

The bioreduction of hexavalent chromium (Cr(VI)) depends highly on bacterial activity, while the release of copper nanoparticles (Cu NPs) poses threats to microorganisms in the environment. This work demonstrated that Cr(VI) reduction efficiency of Shewanella oneidensis MR-1 was remarkably enhanced by 83.7% under 20 mg/L Cu NPs exposure. Cu NPs improved the electron migration capacity of Shewanella oneidensis MR-1 by enhancing bioelectrochemical performance and flavin mononucleotide secretion. Moreover, key genes related to extracellular electron transfer pathways, including direct electron transfer through outer-membrane proteins, flavin-mediated electron transfer, and conductive flagella, were generally upregulated under Cu NPs exposure. In addition, environmental adaptability of Shewanella oneidensis MR-1 was enhanced under Cu NPs exposure by improving environmental information processing and energy and reducing power production, promoting Cr(VI) reduction by Shewanella oneidensis MR-1. This work indicated that Cu NPs could enhance Cr(VI) reduction by Shewanella oneidensis MR-1 through regulating extracellular electron transfer and environmental adaptability.

Bio-immobilization and recovery of chromium using a denitrifying biofilm system: Identification of reaction zone, binding forms and end products

Chromium is an important resource in strategic metals. Different from most studies focusing on the bio-reduction of hexavalent chromium [Cr(VI)], this study aims to achieve the immobilization and recovery of chromium using a sequencing batch biofilm reactor. Results showed that Cr(VI) removal efficiency remained more than 99%, and 97% of reduced Cr(III) was immobilized in the biofilm. Immobilization zone, chromium forms and extracellular polymeric substances composition changes were combined to reveal the mechanism of Cr(VI) reduction and immobilization. The chromium distribution in biofilm demonstrated that intercellular layer was the main active zone with an immobilization amount of 891.70±126.32 mg/g-VSS. The reduced products analysis confirmed that trivalent chromium [Cr(III)] chelated with carboxyl, amino and other functional groups and immobilized in the form of organic Cr(III). The digestion method realized a chromium recovery efficiency of 74.59%. This study provides an alternative method for the bioremediation and resources recovery in chromium polluted wastewater.

Investigation on mechanism of Hexavalent chromium bioreduction by Escherichia sp. TH-1 and the stability of reduction products

Hexavalent chromium (Cr(VI)) was proved to be a carcinogen to organisms and threaten health of human beings through food chains. In order to detect a more economical and efficient method to remove Cr(VI) from contaminated sites, a Cr(VI) reducing strain named TH-1 was isolated from aerobic activated sludge and identified as Escherichia sp. by 16 S rDNA sequence analysis. The Cr(VI) removing performance of TH-1 was elucidated under different environmental conditions (temperature, pH, initial Cr (VI) concentration and metal ions) to detect the optimum condition, and the potential mechanisms of Cr(VI) reduction were explained including micro-characterization and stability test of reduction product. As the result, while inhibited by Cd2+ existence, TH-1 could grow and remove Cr(VI) in a wide range of temperature and pH (optimum at 37 ℃ and pH7.0), with the process being promoted by Cu2+, Ni2+ and Fe3+. The results of X-ray Diffraction, X-ray photoelectron spectroscopy confirmed that the reduced Cr(VI) product was mainly organic-Cr (III) complex, and Fourier Transform infrared spectroscopy showed that functional groups such as –OH, -COOH and CO etc. were Cr binding sites. Afterwards, the stability of the organic-Cr (III) complex reduced by strain TH-1 were much more stable than Cr (III) chemically reduced by FeS, the stability of which decreased significantly from pH 9 to pH 14, but rarely changed under near-neutral and acidic condition. Hence, TH-1 had great prospects for reducing Cr (VI) under different environmental conditions with long-term effect, which was significant for the remediation of Cr (VI) influenced environmental sites.

Bioreduction of hexavalent chromium by a novel haloalkaliphilic Salipaludibacillus agaradhaerens strain NRC-R isolated from hypersaline soda lakes.

The online version contains supplementary material available at 10.1007/s13205-021-03082-2.

Bio-reduction of hexavalent chromium by an indigenous green alga and its impact on the germination of rice seed in chromium enriched environment

Rapid mining activities in Sukinda mining area have generated a huge amount of toxic Cr(VI) which accumulated and persisted in the soil for decades and reduced rice plant productivity in adjoining agricultural fields. Hence, for the bioremediation of rice field soil, a Cr(VI) resistant, thermotolerant and fast-growing native green algal strain SM1 was selected, which rendered resistance to 60 ppm of Cr(VI). DPC assay, ICP-OES and Raman-Spectroscopic analysis confirmed 92.765% of Cr(VI) reduction within 48 h by SM1 under optimized condition. Moreover, Cr(VI) adsorption by the green alga was also established by FTIR and SEM-EDX analysis. The alga (SM1) was identified as Chlorella thermophila by 18S rDNA sequencing (MN855377). Its application significantly improved rice (Oryza sativa var. Lalata) seed germination, seedling growth, seed vigor index, pigment and protein content. CHNS(O) and ICP-OES analysis of the algal biomass depicted the presence of several organic and inorganic compounds, which can be utilized as bio-fertilizer for the rice seedlings. Field experiments on rice plant growth characteristics should be conducted to utilize this potent algal strain in chromium contaminated rice fields for the bio-reduction of Cr(VI) and improvement of rice crop productivity.

Bioreduction of hexavalent chromium on goethite in the presence of Pseudomonas aeruginosa

The effective mineral absorption and bioreduction were considered as two preferred processes to alleviate the bioavailability and toxicity of toxic trace metals. In this study, the bioreduction of hexavalent chromium (Cr(VI)) on goethite (FeOOH) in the presence of Pseudomonas aeruginosa (P. aeruginosa) was investigated with different environmental factors, including carbon source concentrations, pH, temperature and initial Cr(VI) concentrations. The characterization of FeOOH–P. aeruginosa indicated that P. aeruginosa was surrounded by FeOOH, which could provide the essential iron for bacterial growth and reduce Cr(VI) to Cr(III). The optimal experimental conditions for Cr(VI) (initial concentration: 35 mg L−1) absorption (∼46%) and bioreduction (∼54%) involved a temperature of 45 °C and pH of 5.5. Meanwhile, extracellular polymeric substances (EPS) secreted by P. aeruginosa and its functional groups played important roles in the reduction of Cr(VI). They could reduce Cr(VI) to Cr(III) and transform to Cr(OH)3 or Fex-Cr(1-x)(OH)3 precipitation. These results of this study are of significant importance to better understand the environmental geochemical behavior of Cr(VI) with the interactions between soil minerals and microorganisms.

Bioreduction of hexavalent chromium: Effect of compost-derived humic acids and hematite

Composting can enhance the nutrient elements cycling and reduce carbon dioxide production. However, little information is available regarding the application of compost for the remediation of the contaminated soil. In this study, we assess the response of the redox capacities (electron accepting capacities (EAC) and electron donating capacities (EDC)) of compost-derived humic acids (HAs) to the bioreduction of hexavalent chromium (Cr(VI)), especially in presence of hematite. The result showed that the compost-derived HAs played an important role in the bioreduction of Cr(VI) in presence and absence of hematite under the anoxic, neutral (pH 7) and motionless conditions. Based on the pseudo-first order kinetic model, the rate constants of Cr(VI) reduction increased by 1.36–2.0 times when compost-derived HAs was added. The redox capacity originating from the polysaccharide structure of compost-derived HAs made them effective in the direct Cr(VI) reduction (without MR-1) at pH 7. Meanwhile, the reduction rates were inversely proportional to the composting treatment time. When iron mineral (Fe2O3) and compost-derived HAs were both present, the rate constants of Cr(VI) reduction increased by 2.35–5.09, which were higher than the rate of Cr(VI) reduction in HA-only systems, indicating that the hematite played a crucial role in the bioreduction process of Cr(VI). EAC and quinonoid structures played a major role in enhancing the bioreduction of Cr(VI) when iron mineral and compost-derived HAs coexisted in the system. The results can extend the application fields of compost and will provide a new insight for the remediation of Cr(VI)-contaminated soil.

Bioreduction of hexavalent chromium by chromium resistant alkalophilic bacteria isolated from tannery effluent

Two chromium resistant alkalophilic bacterial strains (CRAB), namely Bacillus cohnii SR2 and Bacillus licheniformis SR3 were isolated and identified from tannery effluent. Bioreduction of chromium (VI) into chromium (III) by CRAB was investigated in the present study. Optimization of process parameters with respect to bioreduction percentage was studied by Response Surface Methodology (RSM) software, v12. Both the strains were found to achieve highest chromium (VI) bioreduction of 94 and 95% in 100 mg/L at the end of 25 h at pH 9.0. At an optimized concentration of 550 mg/L, a maximum bioreduction of 82 and 90% by SR2 and SR3 was noted within 25 h. In addition, both the strains showed tolerance to chromium until 1000 mg/L. Scale-up studies using Air lift bioreactor system by CRAB with real tannery effluent showed 100% bioreduction within 8 h. Therefore, this study signified the astonishing bioreduction capability of CRAB isolates that was quite evident in scale-up studies too.

Feasibility and mechanism of microbial-phosphorus minerals-alginate immobilized particles in bioreduction of hexavalent chromium and synchronous removal of trivalent chromium

Chromium(VI) contaminated groundwater has become an increasingly prominent problem due to its extensive application in industry. Based on the easy-loss defect of microbial in practical application and previous research on the coupling enhancement of Cr(VI) bioreduction by phosphorus minerals, Microbial-Phosphorus minerals-Alginate (MPA) immobilized particles were proposed and investigated in this study. The feasibility of MPA immobilized particles were proved, with the higher reduction efficiency, lower phosphorus surplus, significant 94% of total Cr reduction and 85% of intragranular fixation. These superiorities were also obtained at different pH and initial Cr(VI) concentration conditions. Furthermore, the mechanisms of the enhancement of MPA were investigated from microbial level (microbial biomass, antioxidase, gene expression and microbial community analysis) and physics level (adsorption kinetic and isotherm), where the speculation that the reduction mainly took place outside the particles was proposed. This research provides a new approach for the practical application of Cr(VI)-contaminated groundwater in-situ bioremediation.

Exploration of the reduction mechanism of Cr(VI) in anaerobic hydrogen fermenter

The bio-reduction of hexavalent chromium (Cr(VI)) by anaerobic fermentation is considered as a promising, low-cost and environment-friendly way. However, it is unclear for the reduction mechanisms of Cr(VI) in an anaerobic hydrogen fermenter, such as reduction kinetics, related electron donors, migration and transformation, reduction site and key components, and related microorganisms. To clarify these issues, a hydrogen fermenter was designed to reduce Cr(VI) at 55 °C with glucose as initial substrate. Results show that 100 mg/L Cr(VI) can be completely reduced (99.5%) to trivalent chromium (Cr(III) through chemical and biological reactions. Bio-reduction dominates Cr(VI) removal in a first-order exponential decay mode with both glucose and its metabolites (volatile fatty acids) as electron donors. Moreover, volatile fatty acids are more suitable as electron donors for Cr(VI) bio-reduction than glucose. Bacilli, Clostridia and Thermotogae in the fermenter dominated the reduction of Cr(VI) by regulating the production and composition of extracellular polymers (EPSs), in which carboxyl and hydroxyl groups play an important role for Cr(VI) reduction by coordination. The results can guide us to regulate the bio-reduction of Cr(VI), and provide reference for the development of bio-reduction technology of Cr(VI).

Bioreduction of hexavalent chromium using a novel strain CRB-7 immobilized on multiple materials

In this study, a novel Cr(VI) tolerant strain CRB-7 identified as Bacillus sp., was isolated and characterized for its high Cr(VI) reduction. The strain CRB-7 grew well and effectively reduced Cr(VI) under various conditions including pH (7-9), temperature (30-40 °C) and Cr(VI) concentrations (50-250 mg L-1). It almost completely reduced 120 mg L-1 Cr(VI) within 48 h under optimized condition of pH 7 and 37 °C. Further characterization by SEM-EDS and FTIR analyses indicated Cr(VI) removal mechanism of CRB-7 was predominately via bioreduction with little amount of bioadsorption. Furthermore, the strain CRB-7 based immobilized biobeads were successfully synthesized using five different porous materials as bacterial loading carrier respectively to ascertain the optimal immobilization biocomposite for Cr(VI) removal. CRB-7 cells immobilized with 3% sodium alginate (SA) and 5% humic acid (HA) exhibited the highest Cr(VI) removal efficiency. Moreover, immobilized biobeads have the advantages over free cells in being more stable and easier to reuse. High Cr(VI) reducing ability of the free and immobilized CRB-7 cells suggest the strain CRB-7, especially the B-HA-SA biocomposite is promising for remediating Cr(VI)-contaminated sites.

Bioreduction of toxic hexavalent chromium by novel indigenous microbe Brevibacillus agri isolated from tannery wastewater

The present study is focused on the microbial bioreduction of hexavalent chromium generated from tannery waste. For the study, the treated and untreated tannery effluents were collected from an unexplored site of Manpura, Macheri, Jaipur (India). A few bacterial strains capable of tolerating and reducing hexavalent chromium were isolated, and the most capable one that reduced 85% of hexavalent chromium was identified to be Brevibacillus agri by 16S rDNA gene sequencing. This isolate could tolerate high concentrations of chromium up to 850 mg/l of potassium dichromate and showed maximum reduction of about 85% for 100 mg/l of hexavalent chromium at temperature 37 °C and pH 7.0 in 48 h. The potential of the partially purified enzyme to reduce hexavalent chromium was measured by diphenyl carbazide assay. Purified enzyme showed 0.26 units bioactivity to reduce Cr, in the presence of reduced nicotinamide adenine dinucleotide and Km and Vmax were observed to be 1.9 mM and 0.045 mM/min (mg protein), respectively. The current study, therefore, showed Brevibacillus agri capable of reducing hexavalent chromium without usage of toxic chemicals and, henceforth, prevented generation of harmful by-products.

Iron(III) minerals and anthraquinone-2,6-disulfonate (AQDS) synergistically enhance bioreduction of hexavalent chromium by Shewanella oneidensis MR-1

Bioreduction of hexavalent chromium (Cr(VI)) to sparingly soluble trivalent chromium (Cr(III)) is a strategy for the remediation of Cr(VI) contaminated sites. However, its application is limited due to the slow bioreduction process. Here we explored the potential synergistic enhancement of iron(III) minerals (nontronite NAu-2, ferrihydrite, and goethite) and electron shuttle anthraquinone-2,6-disulfonate (AQDS) on the bioreduction of Cr(VI) by Shewanella oneidensis MR-1. AQDS alone increased the bioreduction rate of Cr(VI) by accelerating electron transfer from MR-1 to Cr(VI). Iron minerals alone did not increase the bioreduction rate of Cr(VI), where the electron transfer from MR-1 to Fe(III) minerals was inhibited due to the toxicity of Cr(VI) to MR-1. AQDS plus NAu-2 or ferrihydrite significantly enhanced the bioreduction rate of Cr(VI) as compared to AQDS or NAu-2/ferrihydrite alone, demonstrating that AQDS plus NAu-2/ferrihydrite had the synergistic effect on bioreduction of Cr(VI). Synergy factor (kcells+Fe+AQDS/(kcells+Fe + kcells+AQDS)) was used to quantify the synergistic effect of AQDS and iron minerals on the bioreduction of Cr(VI). The synergy factors of AQDS plus NAu-2 were 2.09–4.63 (three Cr(VI) spikes), and the synergy factors of AQDS plus ferrihydrite were 1.89–4.61 (two Cr(VI) spikes). In the presence of Cr(VI), AQDS served as the electron shuttle between MR-1 and iron minerals, facilitating the reduction of Fe(III) minerals to Fe(II). The synergistic enhancement of AQDS and NAu-2/ferrihydrite was attributed to the generated Fe(II), which could quickly reduce Cr(VI) to Cr(III). Our results provide an attractive strategy to strengthen the bio-immobilization of Cr(VI) at iron-rich contaminated sites through the synergistic enhancement of iron(III) minerals and electron shuttle.

Hexavalent Chromium Bioreduction and its Functional Characterization Using Vigna radiata

Hexavalent Chromium Bioreduction and its Functional Characterization Using Vigna radiata

Recent bioreduction of hexavalent chromium in wastewater treatment: A review

Abstract Hexavalent chromium (Cr(VI)) in water is a proven carcinogen to different internal and external organs of the living organisms. There are different human activities incorporated to the anthropogenic sources in the environment enriching Cr(VI) of high concentration in the water system above the regulatory level. The physical, chemical and biological properties of chromium favour the dissolution in the water environment. This concerns the environmental researcher to tackle and mitigate. Chemical or biological techniques or a combination of the two have been used to remove Cr(VI) from polluted waters. Biological techniques include integrated bioremediation, such as the primary processes of direct bioreduction and biosorption, and secondary processes of microbial fuel cell, biostimulation, surface modified dry biomass and biochar adsorption, and engineered biofilm and cell free reductase. These techniques are used by a wide range of living organisms including bacteria, fungi, plants, plant leaves, plant nuts and algae. This group of living organisms transform and remove Cr(VI) from water during the cellular metabolisms, extracellular activities, physical and chemical adsorptions on the cell surface, and photosynthesis. Variation of different physical, chemical and environmental parameters affecting the efficiency of the bioremediation process have impacted on the design of bioreactors. There has been a recent development of a microbial fuel cell which use the proximity of Cr(VI) reduction as a cathode half cell for the generation of renewable energy and simulation of its’ removal from water.

Hexavalent chromium bioreduction and chemical precipitation of sulphate as a treatment of site-specific fly ash leachates

Most of the power generation globally is by coal-fired power plants resulting in large stockpiles of fly ash. The trace elements associated with the ash particles are subjected to the leaching effects of precipitation which may lead to the subsequent contamination of surface and groundwater systems. In this study, we successfully demonstrate an efficient and sustainable dual treatment remediation strategy for the removal of high levels of Cr6+ and SO42- introduced by fly ash leachate generated by a power station situation in Mpumalanga, South Africa. The treatment consisted of a primary fixed-bed bioreactor kept at a reduction potential for Cr6+ reduction. Metagenome sequencing clearly indicated a diverse bacterial community containing various bacteria, predominantly of the phylum Proteobacteria which includes numerous species known for their ability to detoxify metals such as Cr6+. This was followed by a secondary BaCO3/dispersed alkaline substrate column for SO42- removal. The combination of these two systems resulted in the removal of 99% Cr6+ and 90% SO42-. This is the first effective demonstration of an integrated system combining a biological and chemical strategy for the remediation of multi-contaminants present in fly ash leachate in South Africa.

Nano-sized Fe2O3/Fe3O4 facilitate anaerobic transformation of hexavalent chromium in soil–water systems

The purpose of this study is to investigate the effects of nano-sized or submicro Fe2O3/Fe3O4 on the bioreduction of hexavalent chromium (Cr(VI)) and to evaluate the effects of nano-sized Fe2O3/Fe3O4 on the microbial communities from the anaerobic flooding soil. The results indicated that the net decreases upon Cr(VI) concentration from biotic soil samples amended with nano-sized Fe2O3 (317.1±2.1mg/L) and Fe3O4 (324.0±22.2mg/L) within 21days, which were approximately 2-fold of Cr(VI) concentration released from blank control assays (117.1±5.6mg/L). Furthermore, the results of denaturing gradient gel electrophoresis (DGGE) and high-throughput sequencing indicated a greater variety of microbes within the microbial community in amendments with nano-sized Fe2O3/Fe3O4 than the control assays. Especially, Proteobacteria occupied a predominant status on the phylum level within the indigenous microbial communities from chromium-contaminated soils. Besides, some partial decrease of soluble Cr(VI) in abiotic nano-sized Fe2O3/Fe3O4 amendments was responsible for the adsorption of nano-sized Fe2O3/Fe3O4 to soluble Cr(VI). Hence, the presence of nano-sized Fe2O3/Fe3O4 could largely facilitate the mobilization and biotransformation of Cr(VI) from flooding soils by adsorption and bio-mediated processes.