Chromate removal by yeasts isolated from sediments of a tanning factory and a mine site in Argentina

Twenty-one yeast-like microorganisms were isolated from tannery effluents and from a nickel–copper mine in Argentina. They were tested for their Cu(II), Ni(II), Cd(II) and Cr(VI) tolerance in qualitative assays on solid medium. Three isolates were selected for their multiple tolerance to the different heavy metals and highest tolerance to Cr(VI). According to morphological and physiological analysis and 26S rDNA D1/D2 domain sequences the isolates were characterized as: Lecythophora sp. NGV-1, Candida sp. NGV-9 and Aureobasidium pullulans VR-8. Resistance of the three strains to high Cr(VI) concentrations and their ability to remove Cr(VI) were assessed using YNB-glucose medium supplemented with 0.5 and 1 mM Cr(VI). Chromate removal activity was estimated by measuring remaining Cr(VI) concentration in the supernatant using the colorimetric 1,5-diphenylcarbazide method and total chromium was determined by flame atomic absorption spectroscopy. The results indicate that the initial Cr(VI) concentration negatively influenced growth and the specific growth rate but stimulated the metabolic activity of the three strains; resistance to Cr(VI) by these strains was mainly due to reduction of Cr(VI) rather than chromium bioaccumulation. This study showed the potential ability of these strains as tools for bioremediation of Cr(VI) from contaminated sites.     

Spectroscopic investigations of U(VI) species sorbed by the green algae Chlorella vulgaris

The green alga Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 40% of the uranium are bound by the algal cells. The uranium removal is almost complete at pH 5 and 6 under the given experimental conditions. Scanning electron microscopy and laser-induced fluorescence spectroscopy were used to characterize uranyl species formed in the selected pH range. The micrographs show a regular distribution of U(VI) on the cell surface. Fluorescence spectroscopic investigations of formed algal uranyl complexes indicate that the binding of U(VI) to carboxyl groups plays a dominating role at pH 3, whereas a minor impact of organic phosphate compounds on the U(VI) sorption cannot be excluded. In contrast, at pH 5 and 6 the phosphate groups are mainly responsible for the removal and binding of U(VI) by formation of organic and/or inorganic uranyl phosphates.     

Modeling hexavalent chromium removal in a Bacillus sp. fixed-film bioreactor

A one-dimensional diffusion-reaction model was developed to simulate Cr(VI) reduction in a Bacillus sp. pure culture biofilm reactor with glucose as a sole supplied carbon and energy source. Substrate utilization and Cr(VI) reduction in the biofilm was best represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the (fourth-order) Runge-Kutta method adjusted for mass transport resistance using the (second-order) Crank-Nicholson and Backward Euler finite difference methods. A heuristic procedure (genetic search algorithm) was used to find global optimum values of Cr(VI) reduction and substrate utilization rate kinetic parameters. The fixed-film bioreactor system yielded higher values of the maximum specific Cr(VI) reduction rate coefficient and Cr(VI) reduction capacity (kmc = 0.062 1/h, and Rc = 0.13 mg/mg, respectively) than previously determined in batch reactors (kmc = 0.022 1/h and Rc = 0.012 mg/mg). The model predicted effluent Cr(VI) concentration well with 98.9% confidence (sigmay2 = 2.37 mg2/L2, N = 119) and effluent glucose with 96.4 % confidence (sigmay(w)2 = 5402 mg2/L2, N = 121, w = 100) over a wide range of Cr(VI) loadings (10-498 mg Cr(VI)/L/d).     

Magnesium-induced biofilm development in Arthrobacter sp. SUK 1201 and removal of hexavalent chromium

This study reports the influence of Mg ions on the development and architecture of biofilms by a chromium resistant and reducing bacterium Arthrobacter sp. SUK 1201 and their utilization in the removal of toxic hexavalent chromium. Among the different metal ions tested, Mg(II) greatly influenced the biofilm growth in peptone yeast extract glucose medium. Both Scanning and Confocal Laser Scanning Microscopy revealed that biofilms formed under the induction of Mg(II) had characteristic higher cell densities. The cells remain embedded in thick porous layers of extracellular polymeric substances as evident from the fluorescein isothiocyanate labeled lectin concanavalin A and 4, 6- diamino-2-phenylindole staining. COMSTAT analysis also indicated maximum thickness and roughness coefficient of the biofilm grown in presence of Mg(II). Biofilms of Arthrobacter sp. SUK 1201 developed under such Mg (II) influenced condition showed complete removal of 0.5 mM Cr(VI) in mineral salts medium. The biofilm of this isolate grown in presence of Mg(II) was also able to remove 60µM Cr(VI) from mine seepage water suggesting its possible implication in effective bioremediation of chromium polluted environments.     

Modeling, simulation, and experimental validation for continuous Cr(VI) removal from aqueous solutions using sawdust as an adsorbent

Continuous adsorption experiments were performed in a fixed-bed adsorption column to evaluate the performance of low-cost adsorbent (sawdust) developed for the removal of Cr(VI) from aqueous solutions. The effects of influencing parameters such as flow rate, mass of adsorbent, initial Cr(VI) concentration were studied and the corresponding breakthrough curves were obtained. The fixed-bed adsorption process parameters such as breakthrough time, total percentage removal of Cr(VI), adsorption exhaustion rate and fraction of unused bed-length were obtained. A mathematical model for fixed-bed adsorption column was proposed by incorporating the effect of velocity variation along the bed-length in the existing model. Pore and solid diffusion models were used to describe the intra-particle mechanism for Cr(VI) adsorption. The proposed mathematical model was validated with the literature data and the experimental data obtained in the present study and the model was found to be good for explaining the behavior of breakthrough curves.     

‘Turn‐off’ fluorescence strategy for determination of hexavalent chromium ions based on copper nanoclusters

Cu nanoclusters (CuNCs) capped by tannic acid (TA) (CuNCs@TA) can be used as a highly sensitive fluorescent probe for Cr(VI) detection. Therefore, a fluorescence detection method for Cr(VI) can be established according to the fluorescence quenching of CuNCs@TA that is caused immediately after the addition of Cr(VI). The fluorescence quenching efficiency of CuNCs@TA was linearly correlated with Cr(VI) concentration within the range 0.03–60 μM, and the detection limit for Cr(VI) was 5 nM. This method was demonstrated to be suitable for detecting Cr(VI) in actual water samples. We found that sodium thiosulfate (ST) can redox with Cr(VI) and therefore restore the fluorescence of CuNCs@TA. The mechanism of CuNCs@TA fluorescence quenching and enhancement by Cr(VI) and ST was investigated in detail. The ‘turn‐on’ fluorescent sensor is of practical significance and has broad application prospects.     

Bioremoval of hexavalent chromium from water by a salt tolerant bacterium, Exiguobacterium sp. GS1

Pollution of terrestrial surfaces and aquatic systems by hexavalent chromium, Cr(VI), is a worldwide public health problem. A chromium resistant bacterial isolate identified as Exiguobacterium sp. GS1 by 16S rRNA gene sequencing displayed high rate of removal of Cr(VI) from water. Exiguobacterium sp. GS1 is 99% identical to Exiguobacterium acetylicum. The isolate significantly removed Cr(VI) at both high and low concentrations (1–200 μg mL⁻¹) within 12 h. The Michaelis–Menten K _m and V _max for Cr(VI) bioremoval were calculated to be 141.92 μg mL⁻¹ and 13.22 μg mL⁻¹ h⁻¹, respectively. Growth of Exiguobacterium sp. GS1 was indifferent at 1–75 μg mL⁻¹ Cr(VI) in 12 h. At initial concentration of 8,000 μg L⁻¹, Exiguobacterium sp. GS1 displayed rapid bioremoval of Cr(VI) with over 50% bioremoval in 3 h and 91% bioremoval in 8 h. Kinetic analysis of Cr(VI) bioremoval rate revealed zero-order in 8 h. Exiguobacterium sp. GS1 grew and significantly reduced Cr(VI) in cultures containing 1–9% salt indicating high salt tolerance. Similarly the isolate substantially reduced Cr(VI) over a wide range of temperature (18–45  °C) and initial pH (6.0–9.0). The T _opt and initial pH_opt were 35–40  °C and 7–8, respectively. Exiguobacterium sp. GS1 displayed a great potential for bioremediation of Cr(VI) in diverse complex environments.     

Uptake of hexavalent chromium by bovine erythrocytes and its interaction with cytoplasmic components; The role of glutathione

Hexavalent chromium (Cr(VI)) anion gradually penetrated into bovine erythrocytes and bound with cytoplasmic components. Its penetration was strongly inhibited by the NH₂-reactive agent, 4-acetamido-4′-isothiocyano-stilbene-2,2′-disulfonic acid (SITS) and the SH-reactive agent, N-ethylmaleimide (NEM). Gel filtration showed that the intracellular component that bound to chromium was hemoglobin.

The binding affinity of Cr(VI) to hemoglobin in the absence of glutathione in vitro was found to be much less than in intact erythrocytes. However, in the presence of glutathione, the binding affinity of Cr(VI) to hemoglobin became much higher. This indicates that reduction of hemoglobin or Cr(VI) by glutathione is involved in the binding.

Cr(VI) interacted only weakly with the membrane and did not cause hemolysis of bovine erythrocytes, unlike heavy metals such as Hg²⁺.     

Identification of teratogenic polymethoxy-1-alkenes from Cylindrospermopsis raciborskii,and taxonomically diverse freshwater cyanobacteria and green algae

Cylindrospermopsis raciborskii is among the most commonly recognized toxigenic cyanobacteria associated with harmful algal blooms (HAB) in freshwater systems, and specifically associated with multiple water-soluble toxins. Lipophilic metabolites from C. raciborskii, however, were previously shown to exert teratogenicity (i.e. inhibition of vertebrate development) in the zebrafish (Danio rerio) embryo model, specifically suggesting the presence of additional bioactive compounds unrelated to the currently known toxins. In the present study, a series of known teratogenic polymethoxy-1-alkenes (PMA) were identified, purified and chemically characterized from an otherwise well-characterized strain of toxigenic C. raciborskii. Although PMA have been previously identified in other cyanobacteria, this is the first time they have been identified from this recognized HAB species. Following their identification from C. raciborskii, the taxonomic distribution of the PMA was additionally investigated by chemical screening of a freshwater algal (i.e. cyanobacteria, green algal) culture collection. Screening suggests that these compounds are distributed among phylogenetically diverse taxa. Furthermore, parallel screening of the algal culture collection, using the zebrafish embryo model of teratogenicity, the presence of PMA was found to closely correlate with developmental toxicity of these diverse algal isolates. Taken together, the data suggest PMA contribute to the toxicity of C. raciborskii, as well as apparently several other taxonomically disparate cyanobacterial and green algal genera, and may, accordingly, contribute to the toxicity of diverse freshwater HAB.     

Extraction and physico-chemical characterization of a versatile biodegradable polysaccharide obtained from green algae

During the last years, considerable attention has been given to different marine organisms, like algae, as potential sources of valuable materials. The continuous demand for novel materials and technologies is high and research on the underexploited marine green algae, including its polysaccharidic part—ulvan, has increased accordingly. In this research work, a novel method for extraction of ulvan from green algae is proposed and demonstrated successfully. Different characterization techniques were employed to characterize the isolated algal polysaccharide, namely, on what concerns its thermal trace and crystallinity. Upon heating, ulvan behaves as a non-meltable polysaccharide that is thermally stable before degradation at 220 °C. Ulvan is semi-crystalline in nature and possesses high hygroscopic features, as revealed in this research work. Due to its properties, ulvan can be considered, pure or modified, as a versatile biodegradable polymer for different applications, including tissue engineering and regenerative medicine.     

Contamination level and potential health risk assessment of hexavalent chromium in soils from a coal chemical industrial area in Northwest China

Abstract

This study aimed to evaluate the total Cr and Cr(VI) contamination levels and assess the possible health risk of Cr(VI) in soils from a coal chemical industrial area in Northwest China. The contamination factor (CF) was used to calculate the total Cr and Cr(VI) contamination levels in soils from the study area. The highest concentration of Cr(VI) (69.58?mg/kg) was found in the top soil (0–20?cm) with the distance of 10 m to the coal cinder heap. The carcinogenic risk (CR) and hazard quotient (HQ) were estimated for health risk to workers by using “Chinese Technical Guidelines for Risk Assessment of Contaminated Sites (HJ 25.3-2014).” The results showed that the soils from the study area were moderately polluted by the total Cr and Cr(VI). There was no serious non-CR (HQ < 1). However, the CR values of Cr(VI) were significantly higher than the threshold value, indicating that workers are facing serious threat of Cr(VI). Inhalation (70.32%) was the main exposure pathway to CR, followed by dermal contact (20.64%), and then ingestion (9.04%). These results provide basic information of Cr(VI) pollution control and environment management in coal chemical industrial areas.     

Senna auriculata L. flower petal biomass: An alternative green biosorbent for the removal of fluoride from aqueous solutions

Fluoride contamination in groundwater is a major concern in many parts of India and all over the world. Researches paying attention for the removal of fluoride through the application of biosorbents prepared from different parts of plants are finding greater scope and importance. The present research work focuses on Senna auriculata L., flower petal biomass as biosorbent, and evaluated its feasibility for fluoride ion elimination from aqueous solutions. Batch experiments were conducted to remove fluoride under different experimental conditions have been optimized for the maximum removal of fluoride; 80% removal was observed at pH: 6, sorbent dosage: 0.25 g/100 mL, time of agitation: 90 min, and initial concentration of the fluoride ions: 5 mg/L. Characterization studies of the biosorbent revealed its favorability towards the sorption of fluoride. In the isothermal modeling studies, Langmuir isotherm model was obeyed by the biosorption process with R² value of 0.98 and from a kinetic perspective, the biosorption of fluoride onto the biosorbent observed the pseudo-second-order reaction with R² value of 0.98. The developed biosorbent has been applied to real field fluoride-contaminated water samples and found to be successful.     

Fabrication of hybrid biosorbent nanoscale zero-valent iron-Sargassum swartzii biocomposite for the removal of crystal violet from aqueous solution

A novel nanoscale zero-valent iron-Sargassum swartzii (nZVI-SS) biocomposite was synthesized and evaluated for its ability to adsorb crystal violet (CV) from aqueous solutions. Involvement of various functional groups of the biosorbent in preferential adsorption of cationic dye was observed using Fourier transform infrared (FTIR) spectroscopy. Morphological changes occurring on the biocomposite materials were characterized using scanning electron microscopy (SEM). Significant increase (～90%) in the biosorption of cationic dye was observed with gradual increase in pH of the medium from 3 to 12. The effect of biosorbent concentration, initial pH, temperature, agitation rate, adsorption time, and initial dye concentration was studied for the biosorption of CV using nZVI biocomposite. During the optimization study, maximum biosorption capacity was observed at pH of 8. At various initial CV concentrations (20–100 mg/L), attainment of batch sorption equilibrium was observed within 120 min of reaction time. The Langmuir isotherm model expressed high coefficient of determination (R² = 0.999). The maximum dye uptake of 200 mg/g was reported at pH 8. Kinetics and temperature profiles were evaluated and reported. Desorption study was carried out with 0.1 M HCl. Investigations proved that nZVI-SS is an excellent biosorbent for the sequestration of CV in aqueous media.     

Removal of hexavalent chromium by fungal biomass of <Emphasis Type="Italic">Mucor racemosus</Emphasis>: influencing factors and removal mechanism

This study reported the hexavalent chromium removal by untreated Mucor racemosus biomass and the possible mechanism of Cr (VI) removal to the biomass. The optimum pH, biomass dose, initial Cr (VI) concentration and contact time were investigated thoroughly to optimize the removal condition. The metal removal by the biomass was strongly affected by pH and the optimum pH ranged from 0.5 to 1.0. The residual total Cr was determined. It was found that dichromate reduction occurred at a low very low pH value. At biomass dose 6 g/l, almost all the Cr (VI) ions were removed in the optimum condition. Higher removal percentage was observed at lower initial concentrations of Cr (VI) ions, while the removal capacity of the biomass linearly depended on the initial Cr (VI) concentration. More than half of Cr (VI) ions were diminished within 1 h of contact and removal process reached a relative equilibrium in approximately 8 h. Almost all of the Cr (VI) ions were removed in 24 h when initial concentrations were below 100 mg/l. The equilibrium data were fitted in to the Langmuir and the Freundlich isotherm models and the correlated coefficients were gained from the models. A Fourier transform infrared spectra was employed to elucidate clearly the possible biosorption mechanism as well.     

Simultaneous bioremediation of Cr(VI) and lindane in soil by actinobacteria

Environments co-contaminated with metals and organic compounds are difficult to remediate. Actinobacteria is an important group of microorganisms found in soils, with high metabolic versatility and potential for bioremediation. In this paper, actinobacteria were used to remediate soil co-contaminated with Cr(VI) and lindane. Five actinobacteria, tolerant to Cr(VI) and lindane mixture were selected: Streptomyces spp. A5, A11, M7, and MC1, and Amycolatopsis tucumanensis DSM 45259. Sterilized soil samples were inoculated with actinobacteria strains, either individually or as a consortium, and contaminated with Cr(VI) and lindane, either immediately or after 7 days of growth, and incubated at 30 °C during 14 days. All actinobacteria were able to grow and remove both contaminants, the consortium formed by Streptomyces spp. A5, M7, MC1, and A. tucumanensis showed the highest Cr(VI) removal, while Streptomyces sp. M7 produced the maximum lindane removal. In non-sterile soil samples, Streptomyces sp. M7 and the consortium removed more than 40% of the lindane, while Streptomyces sp. M7 demonstrated the greatest Cr(VI) removal. The most appropriate strategy for bioremediation of Cr(VI) and lindane co-contaminated soils would be the inoculation with Streptomyces sp. M7.     

Cathodic reduction of hexavalent chromium [Cr(VI)] coupled with electricity generation in microbial fuel cells

A novel approach to Cr(VI)-contaminated wastewater treatment was investigated using microbial fuel cell technologies in fed-batch mode. By using synthetic Cr(VI)-containing wastewater as catholyte and anaerobic microorganisms as anodic biocatalyst, Cr(VI) at 100 mg/l was completely removed during 150 h (initial pH 2). The maximum power density of 150 mW/m² (0.04 mA/cm²) and the maximum open circuit voltage of 0.91 V were generated with Cr(VI) at 200 mg/l as electron acceptor. This work verifies the possibility of simultaneous electricity production and cathodic Cr(VI) reduction.     

Isolation and first EPR characterization of the [FeFe]-hydrogenases from green algae

Hydrogenase expression in Chlamydomonas reinhardtii can be artificially induced by anaerobic adaptation or is naturally established under sulphur deprivation. In comparison to anaerobic adaptation, sulphur-deprived algal cultures show considerably higher expression rates of the [FeFe]-hydrogenase (HydA1) and develop a 25-fold higher in vitro hydrogenase activity. Based on this efficient induction principle we have established a novel purification protocol for the isolation of HydA1 that can also be used for other green algae. From an eight liter C. reinhardtii culture 0.52 mg HydA1 with a specific activity of 741 μmol H₂ min^− 1 mg^− 1 was isolated. Similar amounts were also purified from Chlorococcum submarinum and Chlamydomonas moewusii. The extraordinarily large yields of protein allowed a spectroscopic characterization of the active site of these smallest [FeFe]-hydrogenases for the first time. An initial analysis by EPR spectroscopy shows characteristic axial EPR signals of the CO inhibited forms that are typical for the H_ox-CO state of the active site from [FeFe]-hydrogenases. However, deviations in the g-tensor components have been observed that indicate distinct differences in the electronic structure between the various hydrogenases. At cryogenic temperatures, light-induced changes in the EPR spectra were observed and are interpreted as a photodissociation of the inhibiting CO ligand.     

花生壳粉生物吸附水溶液中阴离子染料的研究

An untried,low cost, locally available biosorbent for its anionic dye removal capacity from aqueous solution was investigated. Powder prepared from peanut hull had been used for hiosorption of three anionic dyes, amaranth (Am), sunset yellow (SY) and fast green FCF (FG). The effects of various experimental parameters (e.g.initial pH and dye concentration, sorbent dosage, particle size, ion strength, contact time etc.) were examined and optimal experimental conditions were decided. At initial pH 2.0, three dyes studied could be removed effectively.When the dye concentration was 50 mg" L-1 the percentages of dyes sorbed was 95.5 % in Am, 91.3 % in SY and 94.98 % in FG, respectively. The ratios of dyes sorbed had neared maximum values in all three dyes whensorbent dose of 5.0 g·L^-1 and the sorbent particle size in 80—100 mesh was used. The increasing the ion strength of solution caused the decrease in biosorption percentages of dyes. The equilibrium values arrived at about 36 hour for all three dyes. The isothermal data of biosorption followed the Langmuir and Freundlich models. The biosorption processes conformed the pseudo-first-order rate kinetics. The results indicated that powdered peanut hull was an attractive candidate for removing anionic dyes from dye wastewater.     

花生壳粉作为生物吸附剂去除水溶液中偶氮染料的研究

用低值的花生壳粉作为生物吸附剂对苋菜红、日落黄两种偶氮染料进行了吸附研究,目的是寻求经济的染料废水处理方法。考察了PH、染料浓度、吸附剂量、吸附剂粒径、离子强度和吸附时间等因素对染料吸附的影响,确定了最佳吸附条件。结果显示,初始pH2,两种偶氮染料的去除率较高。吸附等温线符合Langmuir和Freondlich模式,吸附过程符合准一级反应动力学方程。研究结果表明,花生壳是一种很有前途的偶氮染料废水处理生物材料。