Microbial Waste Biomass for Removal of Chromium(VI) from Chrome Effluent

ABSTRACT

Microbial waste biomass, a by-product of the fermentation industry, was developed as a biosorbent to remove hexavalent chromium (Cr) from the acidic effluent of a metal processing industry. In batch sorption, 100% Cr(VI) removal was achieved from aqueous solution in 30 min contact at pH 4.0–5.0. The Cr(VI) sorption equilibrium was evaluated using the Langmuir and Freundlich models, indicating the involvement of ion exchange and physicochemical interaction. Fourier transform infrared (FTIR) analysis revealed the presence of amine, hydroxyl, and imine functional groups present on the surface of microbial biomass that are involved in Cr binding. In a continuous sorption system, 95 mg L^?1 of Cr(VI) was adsorbed before the column reached a breakthrough point of 0.1 mg L^?1 Cr(VI) at the column outlet. An overall biosorption capacity of 12.6 mg Cr(VI) g^?1 of dry microbial waste was achieved, including the partially saturated portion of the dynamic sorption zone. Insignificant change in metal removal was observed up to 10 cycles. In pilot-scale studies, 100% removal of Cr(VI) was observed up to 5 weeks, and the method was found to be cost-effective, commercially viable, and environmentally friendly, as it does not generate toxic chrome sludge.     

Removal of Humic Substances from Aqueous Solution by Fungal Pellets

The removal of humic substances from aqueous solution at pH=4.8 and 6.0 and 25 °C by pure culture of Aspergillus niger has been examined. The removal of humic substances from aqueous phase was monitored by following the decrease in absorbance at 370 nm. COD and fungal growth were also measured. The initial concentration of humic and fulvic acids, pH and diameter of fungal pellets were found to be the most important parameters. The results suggested that decolorization of batch culture was a consequence of several processes. In the first 5 hours for pellets with diameter 1-3 mm and 10 hours for pellets with diameter 2-5 mm adsorption of humic substances was dominant. Afterwards, desorption of slightly bound humic substances and their degradation, as well as degradation of remaining humic substances in the solution, continued simultaneously through the period of 10 days.     

The Suitability of Jatropha Seed Press Cake as a Biosorbent for Removal of Hexavalent Chromium from Aqueous Solutions

Jatropha seed press cake (JPC), a biodeisel waste, was investigated for its use as biosorbent for Cr(VI) removal from wastewater. The acid-pretreated biomass exhibited 1.9-fold higher biosorption efficiency for Cr(VI). The Cr(VI) biosorption efficiency was found to increase with decrease in pH of aqueous medium. The adsorption capacity of biosorbent for Cr(VI) increased with increasing concentration of Cr(VI). The biosorption of Cr(VI) by acid-treated JPC followed a pseudo-second-order kinetics. The results of equilibrium studies showed that the biosorption process fitted the Langmuir isotherm model, with a maximum adsorption capacity of 22.727 mg of Cr(VI)/g of biosorbent at 30°C. The activation energy was found to be 27.114 kJ/mol, suggesting that the adsorption process was mainly a physical process. The important thermodynamic parameters of adsorption (ΔG, ΔH, andΔS) were determined, which indicated that the Cr(VI) sorption by JPC is a spontaneous and endothermic process.     

絮凝酵母吸附Cr(VI) 的机理

絮凝酵母SPSC01为酿酒酵母Saccharomyces cerevisiae和粟酒裂殖酵母Schizosaccharomyces pombe的融合菌株,用其吸附水溶液中的重金属Cr(VI),可以大大降低生物吸附的固液分离成本。为了探讨SPSC01菌体絮凝蛋白对Cr(VI) 还原吸附的影响,对SPSC01与其亲本菌株的吸附行为进行了比较。结果表明,SPSC01和其具有絮凝性状的亲本S. pombe的Cr(VI) 去除速率基本同步,远优于无絮凝性状的亲本S. cerevisiae;达到吸附平衡时,S. pombe、SPSC01和S. cerevisiae对总Cr去除率分别达68.8％、48.6％和37.5％;从而证明了絮凝有利于Cr(VI) 的还原、吸附,絮凝蛋白在Cr(VI) 的还原吸附过程中起促进作用。通过化学屏蔽方法和傅立叶变换红外光谱 (FTIR) 分析,对SPSC01菌体表面吸附Cr(VI) 的机理进行了研究,结果表明SPSC01菌体表面吸附Cr(VI) 起主要作用的基团是氨基、羧基和酰胺基。     

絮凝酵母吸附Cr(VI)的机理

絮凝酵母SPSC01为酿酒酵母Saccharomyces cerevisiae和粟酒裂殖酵母Schizosaccharomyces pombe的融合菌株,用其吸附水溶液中的重金属Cr(VI),可以大大降低生物吸附的固液分离成本。为了探讨SPSC01菌体絮凝蛋白对Cr(VI)还原吸附的影响,对SPSC01与其亲本菌株的吸附行为进行了比较。结果表明,SPSC01和其具有絮凝性状的亲本S.pombe的Cr(VI)去除速率基本同步,远优于无絮凝性状的亲本S.cerevisiae;达到吸附平衡时,S.pombe、SPSC01和S.cerevisiae对总Cr去除率分别达68.8%、48.6%和37.5%;从而证明了絮凝有利于Cr(VI)的还原、吸附,絮凝蛋白在Cr(VI)的还原吸附过程中起促进作用。通过化学屏蔽方法和傅立叶变换红外光谱(FTIR)分析,对SPSC01菌体表面吸附Cr(VI)的机理进行了研究,结果表明SPSC01菌体表面吸附Cr(VI)起主要作用的基团是氨基、羧基和酰胺基。     

Comparative Study of Cr(VI) Removal by Exiguobacterium sp. in Free and Immobilized Forms

Cr(VI) is a toxic environmental pollutant. To determine the potential role of microbes towards chromate bioremediation, two bacterial strains, E1 and E4, that could tolerate Cr(VI) at levels up to 2250 μg ml^?1 were isolated from the soil of a tannery. They were identified as Exiguobacterium sp. To estimate the removal of Cr(VI) using immobilized bacterial cells, 2% sodium alginate and 2.5% agar were used as immobilizing matrices. In the case of sodium alginate, 89% and 93% of Cr(VI) removal by E1 and E4, respectively, were observed. When agar beads were used as an immobilizing matrix, removal was recorded as 39% and 48% for E1 and E4, respectively. Removal of Cr(VI) was also estimated in sterile and nonsterile tannery effluent. More Cr(VI) removal was noted in the nonsterile effluent than in the sterile effluent. The maximum uptake of Cr(VI) of bound cells of E1 and E4 was found to be 17.54 and 20.04 μg ml^?1, respectively. Fourier transform infrared (FTIR) spectra of cells of E4 with Cr(VI), without Cr(VI), and immobilized cells depicted several absorption peaks, mainly for P?OH group, C?H bending, C?O bond, and amide II groups, reflecting the complex nature of the bacterial cells and the contribution of these functional groups to the Cr(VI) binding process.     

Effects of Reductants on Phytoextraction of Chromium (VI) by Ipomoea aquatica

Reductants are often used to reduce Cr(VI) in chemical treatments, yet the effects of the reductants on Cr(VI) phytoremediation are not fully understood. This study investigates the effects of different reductants on Cr(VI) phytoremediation by Ipomoea aquatica in simulated solution with 3 mg L^?1 of Cr(VI), pH₀ of 6, and an incubation time of 5 days. Results indicate that the applications of S₂O₃^2?, Fe⁰, and Fe²⁺ at low doses notably increased root Cr concentrations, which were obviously higher than that those in the control (Cr⁶⁺ alone). However, high reductant concentrations decreased bioaccumulation of Cr in the roots and shoots of the plant.

Statistical results indicate that Cr concentrations were significantly and negatively correlated with Fe concentrations in the roots and shoots of the plant (p < 0.05). This suggest that Fe accumulation inhibited Cr accumulation in the plant. A Cr(VI) concentration of 3 mg L^?1 caused short, brown lateral roots with tip necrosis, leaf chlorosis, and noticeable shoot wilting. The leaf necrosis and shoot wilting is caused by oxidative damage of lateral roots by Cr(VI) rather than by the reactive oxygen species generated by the oxidative stress. Addition of the reductants effectively reduced these plant injuries.     

Preparation of Modified Chitin for the Removal of Chromium(VI)

Chitin was chemically modified into various forms for enhancing chromium sorption. The modified forms of chitin, viz., protonated chitin (PC), carboxylated chitin (CC), and grafted chitin (GC), possessed enhanced chromium sorption capacities (SCs) of 2812, 3010, and 3770 mg/kg, respectively, than the raw chitin (C), which showed the SC of 2316 mg/kg. The sorption experiments were carried out in batch mode to optimize various influencing parameters, viz., contact time, pH, common ions, and temperature. The sorbents were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The modified forms of chitin removes chromium by means of electrostatic adsorption coupled reduction and complexation. The adsorption data were fitted with Freundlich and Langmuir isotherms. The calculated values of thermodynamic parameters indicate the nature of chromium sorption. The dynamic studies demonstrated that the sorption process follows pseudo-second-order and intraparticle diffusion models. The suitability of these modified chitin has been tested with field sample collected from a nearby industrial area.     

Biosorption of Chromium(VI) and Lead(II): Role of Spirulina platensis in the Treatment of Industrial Effluent

Biosorption is the process of removal of any chemical molecules by the treatment of biological material. Industrialization resulted in the discharge of various toxic heavy metals into water bodies, which poses serious health hazards to humans and animals. In the present study, live Spirulina platensis was used as a biosorbent for the removal of the heavy metals chromium (Cr(VI)) and lead (Pb(II)) from the aqueous samples. S. platensis were cultured in the presence of different concentrations of heavy metals. The growth of the algal cells was found to be decreased by 59% and 36% in media containing 50 ppm Cr(VI) and Pb(II), respectively. To assess the biosorption of heavy metals, at different time intervals, the spent culture media were used to detect Cr(VI) by atomic absorption spectroscopy method and Pb(II) by 4-(2-pyridylazo)resorcinol indicator method. Results suggested that there was a significant uptake of Cr(VI) and Pb(II) from the medium by S. platensis, with corresponding decrease of metals in the medium. When metal salt solutions or industrial effluent samples were passed through the column containing immobilized live S. platensis in calcium alginate beads, the concentration of Cr(VI) was found to be reduced drastically. The present study indicates the application of S. platensis for the bioremediation of heavy metals from the samples obtained from industrial effluents.     

Biosorption of uranium(VI) by Aspergillus fumigatus

Aspergillus fumigatus removed uranium(VI) very rapidly and reached equilibrium within 1 h of contact of biomass with the aqueous metal solution. Biosorption data fitted to Langmuir model of isotherm and a maximum loading capacity of 423 mg U g^–1 dry wt was obtained. Distribution coefficient as high as 10,000 (mg U g^–1)/(mg U ml^–1) at a residual metal ion concentration of 19 mg l^–1 indicates its usefulness in removal of uranium(VI) from dilute waste streams. Optimum biosorption was seen at pH 5.0 and was independent of temperature (5–50°C ). Initial metal ion concentration significantly influenced uptake capacity which brought down % (w/w) uranium(VI) removal from 90 at 200 mg U l^–1 to 35 at 1000 mg U l^–1. Presence of 0.84 mmol Fe²⁺, Fe³⁺, Ca²⁺ and Zn²⁺ had no effect on uranium(VI) biosorption unlike Al³⁺ (0.84 mM) which was inhibitory.     

Removal of Chromium(VI) Ions from Synthetic Solutions by the Fungus Penicillium purpurogenum

The ability of Penicillium purpurogenum to bind high amounts of chromium(VI) from aqueous solutions is demonstrated. Cr(VI) adsorption capacity increases with time during the first four hours and then leveled off toward the equilibrium adsorption capacity. Biosorption of Cr(VI) ions reached equilibrium in four hours. Binding of Cr(VI) ions with Penicillium purpurogenum biomass was clearly pH dependent. Cr(VI) loading capacity increased with increasing pH. The adsorption of Cr(VI) ions reached a plateau value at a pH of approx. 6.0. The maximum capacity of adsorption of Cr(VI) ions onto the fungal biomass was 36.5 mg/g. Adsorption behavior of Cr(VI) ions can be approximately described with the Langmuir equation. When applying the Langmuir model, the maximum adsorption capacity (Q_max) and the Langmuir constant were found to be 40 mg/g and 3.9 × 10^–3 mg/L. Elution of Cr(VI) ions was performed by means of 0.5 M HCl. It was possible to use the biomass of Penicillium purpurogenum for six cycles for biosorption.     

Mechanisms of DNA damage and insight into mutations by chromium(VI) in the presence of glutathione

The mechanisms of hexavalent chromium(VI) induced DNA damage were unveiled by detecting products of single- and double-stranded DNA in the presence of glutathione. The absence of a detectable hydroxyl radical in the reactions indicates that DNA damage was exclusively by hypervalent chromium species. Polyacrylamide gel electrophoresis (PAGE) experiments with 32-mer single-stranded oligonucleotide and its complementary duplex revealed cleavages largely at purine bases with significant enhancement of such cleavages in the presence of a base. Quantitative estimations of bases released by HPLC before and after enzymatic digestion with exonucleases unequivocally established the excessive release of purine bases. This release was accompanied by the concomitant formation of phosphoglycolate as characterized by liquid chromatography-mass spectrometry (LC-MS). These data connote that the preponderance DNA damage is due to an oxidation specifically at H4' of the ribose moiety leading to the formation of apurinic sites. In addition to the oxidation at H4', DNA oxidation was also initiated through H5' site as evidenced by the identification of furfural. This pathway appears to be non-selective and more abundant for ssDNA as cleavages were observed at both purine and pyrimidine bases. Finally, the detection of guanidinohydantoin as a minor product points the involvement of an oxygen activated hypervalent chromium species, perhaps a peroxo-chromium species. Both major and minor pathways lead to cleavages at purine sites for ds-DNA and are consistent with the observation that DNA cleavage was enhanced in the presence of a base. In contrast, when hydrogen peroxide was added to the reactions, random DNA cleavages were apparent indicating involvement of multiple species including a hydroxyl radical. These data pinpoint mutation mechanisms induced by chromium(VI) in the presence of glutathione due to transversion either by inserting the wrong bases opposite to the apurinic sites during replication or by purine-purine mismatch.     

Fluorescent sensing platform based on polyethyleneimine-protected copper nanoclusters for detection of chromium(VI) in real samples

A new type of polyethyleneimine-protected copper nanoclusters (PEI-CuNCs) is favorably developed by a one-pot method under mild conditions. The obtained PEI-CuNCs is characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, Fourier-transform infrared (FTIR) spectroscopy and other techniques. It is worth noting that the proposed PEI-CuNCs demonstrate a selective response to chromium(VI) over other competitive species. Fluorescence quenching of PEI-CuNCs is determined to be chromium(VI) concentrations dependence with a low limit of detection of 8.9 nM. What is more, the as-developed PEI-CuNCs is further employed in building a detection platform for portable recognition of chromium(VI) in real samples with good accuracy. These findings may offer a distinctive strategy for the development of methods for analyzing and monitoring chromium(VI) and expand their application in real sample monitoring.     

Moderate selenium dosing inhibited chromium (VI) toxicity in chicken liver

This study aimed to clarify the effect of selenium (Se) on chromium (VI) [Cr(VI)]‐induced damage in chicken liver. A total of 105 chickens were randomly divided into seven groups of 15. Group I received deionized water; group II received Cr(VI) (7.83 mg/kg/d) alone; and other groups orally received both Cr(VI) (7.83 mg/kg/d) and Se of different doses (0.14, 0.29, 0.57, 1.14, and 2.28 mg/kg/d). The levels of superoxide dismutase (SOD), glutathione (GSH), malondialdehyde (MDA), Ca²⁺‐ATPase, and mitochondrial membrane potential (MMP) were measured. Results showed that Cr(VI) increased MDA content and decreased GSH content, T‐SOD activity, Ca²⁺‐ATPase activity, and MMP level. Meanwhile, Se co‐treatment (0.14, 0.29, and 0.57 mg/kg/d) increased the viability of the above indicators compared with Cr(VI)‐treatment alone. In addition, histopathologic examination revealed that Cr(VI) can cause liver damage, whereas Se supplementation of moderate dose inhibited this damage. This study confirmed that Se exerted protective effect against Cr(VI)‐induced liver damage.     

Biogeochemical Elimination of Chromium (VI) from Contaminated Water

Ferrous iron [Fe(II)] reductively transforms heavy metals in contaminated groundwater, and the bacterial reduction of indigenous ferric iron [Fe(III)] to Fe(II) has been proposed as a means of establishing redox reactive barriers in the subsurface. The reduction of Fe(III) to Fe(II) can be accomplished by stimulation of indigenous dissimilatory metal-reducing bacteria (DMRB) or injection of DMRB into the subsurface. The microbially produced Fe(II) can chemically react with contaminants such as Cr(VI) to form insoluble Cr(III) precipitates. The DMRB Shewanella algae BrY reduced surface-associated Fe(III) to Fe(II), which in batch and column experiments chemically reduced highly soluble Cr(VI) to insoluble Cr(III). Once the chemical Cr(VI) reduction capacity of the Fe(II)/Fe(III) couple in the experimental systems was exhausted, the addition of S. algae BrY allowed for the repeated reduction of Fe(III) to Fe(II), which again reduced Cr(VI) to Cr(III). The research presented herein indicates that a biological process using DMRB allows the establishment of a biogeochemical cycle that facilitates chromium precipitation. Such a system could provide a means for establishing and maintaining remedial redox reactive zones in Fe(III)-bearing subsurface environments.     

Biogeochemical Elimination of Chromium (VI) from Contaminated Water

Ferrous iron [Fe(II)] reductively transforms heavy metals in contaminated groundwater, and the bacterial reduction of indigenous ferric iron [Fe(III)] to Fe(II) has been proposed as a means of establishing redox reactive barriers in the subsurface. The reduction of Fe(III) to Fe(II) can be accomplished by stimulation of indigenous dissimilatory metal-reducing bacteria (DMRB) or injection of DMRB into the subsurface. The microbially produced Fe(II) can chemically react with contaminants such as Cr(VI) to form insoluble Cr(III) precipitates. The DMRB Shewanella algae BrY reduced surface-associated Fe(III) to Fe(II), which in batch and column experiments chemically reduced highly soluble Cr(VI) to insoluble Cr(III). Once the chemical Cr(VI) reduction capacity of the Fe(II)/Fe(III) couple in the experimental systems was exhausted, the addition of S. algae BrY allowed for the repeated reduction of Fe(III) to Fe(II), which again reduced Cr(VI) to Cr(III). The research presented herein indicates that a biological process using DMRB allows the establishment of a biogeochemical cycle that facilitates chromium precipitation. Such a system could provide a means for establishing and maintaining remedial redox reactive zones in Fe(III)-bearing subsurface environments.     

Biomonitoring of chromium(VI) deposited in pulmonary tissues: Pilot studies of a magnetic resonance imaging technique in a post-mortem rodent model

The biomonitoring of individuals exposed to chromium(VI) by inhalation is often based on determinations of chromium in body fluids such as blood, plasma or urine, or on assessments of DNA damage in non-lung surrogate tissues such as peripheral blood lymphocytes. These techniques are of some use as biomarkers of internal exposure or biological effect, mainly in the case of soluble chromium(VI) compounds, but they provide at best only indirect information about chromium(VI) concentrations in the main target organ of interest - the lung. An urgent need exists for a non-invasive technique to permit the visualization and quantification of chromium(VI) in the lung of exposed humans. This study details the development of a lung imaging technique based on the detection of paramagnetic chromium using magnetic resonance imaging (MRI). The intracellular reductive conversion of chromium(VI) is a crucial bioactivation step in its carcinogenicity, and the MRI method described here relies on the conversion of non-paramagnetic (MRI 'silent') chromium(VI) to detectable paramagnetic species such as chromium(III). Initial studies with chromium(III) revealed that a range of 2.5-5 μg chromium(III) instilled in rat lung is considered to be the lower limit of detection of this method. It was possible to demonstrate the presence of 30 μg chromium(VI) in our post-mortem rat model. The ultimate objective of this work is to determine whether this technique has applicability to the biomonitoring of chromium(VI) inhalation exposures that result in internalized lung doses in human subjects.     

Biomonitoring of chromium(VI) deposited in pulmonary tissues: Pilot studies of a magnetic resonance imaging technique in a post-mortem rodent model

The biomonitoring of individuals exposed to chromium(VI) by inhalation is often based on determinations of chromium in body fluids such as blood, plasma or urine, or on assessments of DNA damage in non-lung surrogate tissues such as peripheral blood lymphocytes. These techniques are of some use as biomarkers of internal exposure or biological effect, mainly in the case of soluble chromium(VI) compounds, but they provide at best only indirect information about chromium(VI) concentrations in the main target organ of interest – the lung. An urgent need exists for a non-invasive technique to permit the visualization and quantification of chromium(VI) in the lung of exposed humans. This study details the development of a lung imaging technique based on the detection of paramagnetic chromium using magnetic resonance imaging (MRI). The intracellular reductive conversion of chromium(VI) is a crucial bioactivation step in its carcinogenicity, and the MRI method described here relies on the conversion of non-paramagnetic (MRI ‘silent’) chromium(VI) to detectable paramagnetic species such as chromium(III). Initial studies with chromium(III) revealed that a range of 2.5–5 μg chromium(III) instilled in rat lung is considered to be the lower limit of detection of this method. It was possible to demonstrate the presence of 30 μg chromium(VI) in our post-mortem rat model. The ultimate objective of this work is to determine whether this technique has applicability to the biomonitoring of chromium(VI) inhalation exposures that result in internalized lung doses in human subjects.     

Preparation and Characterization of Chemically Modified Silk Cotton Hull Activated Carbon and Its Effects on Cd(II) Removal from Aqueous Solutions

The novel biosorbent silk cotton hull, an agrowaste material, has been successfully utilized for the removal of cadmium(II) from aqueous solutions. The adsorption of cadmium onto three kinds of activated biosorbent has been studied: modified by concentrated sulfuric acid alone (AC), a mixture of concentrated sulfuric acid and hydrogen peroxide (AC1), and a mixture of concentrated sulfuric acid and ammonium persulfate (AC2). The adsorption studies were carried out to optimize the process parameters such as pH, adsorbent dosage, contact time, and initial metal ion concentration. Maximum metal removal was observed at pH 7.0 with a contact time of 90 min at stirring speed of 200 rpm with an adsorbent dosage of 4.0 g L^?1. The sorption isotherms were studied using the Langmuir, Freundlich, and Tempkin isotherm models. The maximum adsorption capacities were 100.00, 142.86, and 142.87 mg g^?1 for AC, AC1, and AC2, respectively. Accordingly, the surface modification of the activated carbons AC1 and AC2 enhanced cadmium removal greatly. The experiments demonstrated that the removal of metal ions followed the pseudo-second-order kinetic model. The sorption mechanism is discussed in terms of the activated surface properties. A relationship between the oxygen content and sorption was found in this novel material. Desorption experiments were carried out using hydrochloric acid with a view to generate the spent adsorbent and to recover the adsorbed metal ions.     

Evaluation of Cr(VI) Exposed and Unexposed Plant Parts of Tradescantia pallida (Rose) D. R. Hunt. for Cr Removal from Wastewater by Biosorption

Phytoremediation is an efficient method for the removal of heavy metals from contaminated systems. A productive disposal of metal accumulating plants is a major concern in current scenario. In this work, Cr(VI) accumulating Tradescantia pallida plant parts were investigated for its reuse as a biosorbent for the removal of Cr(VI) ions. The effect of pH, contact time, sorbent dosage, Cr(VI) concentration and temperature was examined to optimize these process parameters. Results showed that Cr(VI) exposed/unexposed T. pallida leaf biomass could remove 94% of chromium with a sorption capacity of 64.672 mg g^?1. Whereas the kinetics of Cr(VI) biosorption was well explained by the pseudo second-order kinetic model, the Langmuir model better described the data on Cr(VI) sorption isotherm compared with the Freundlich model. The changes in the free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) were found to be ?5.276 kJ mol^?1, 0.391 kJ mol^?1 K^?1 and 11.346 kJ mol^?1, respectively, which indicated the process to be spontaneous, feasible and endothermic in nature. FTIR spectra of T. pallida leaf biomass revealed the active participation of ligands, such as ?NH, amide, hydroxyl and sulphonate groups present in the biomass for Cr(VI) binding, SEM analysis revealed a porous structure of the biosorbent for an easy uptake of Cr(VI).