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A novel sorbent based on 2% grape stalk wastes encapsulated in calcium alginate beads was investigated for the removal of Cr(VI) and Cr(III) from aqueous solutions. The sorbent proved to be efficient for chromium removal in both hexavalent and trivalent forms from aqueous solution at pH 3.0. In binary mixtures, the presence in solution of one of the forms enhances the sorption of the other which results in an increase of the amount of total chromium removed. This study suggests that the proposed sorbent can be used for the removal of chromium from wastewaters through a cost-effective and environmentally friendly process. [ABSTRACT FROM AUTHOR]

The Cr(VI) reducing capability of an acclimated indigenous culture cultivated from primary sludge was evaluated in batch and packed-bed bioreactor systems. Performance evaluation was carried out in unmodified cultures, cultures modified by substituting terminal organisms in the consortium by a known Cr(VI)-reducing organism (Escherichia coil ATCC 33456), and pure cultures of Cr(VI)-reducing organisms. A high Cr(VI) reduction rate was observed in modified cultures and in the pure culture of the Cr(VI)-reducing bacteria (Bacillus sp.). Furthermore, the Bacillus sp. pure culture outperformed both the unmodified and modified consortium cultures in reducing Cr(VI). Abiotic Cr(VI) reduction activity was evaluated in heat-killed and azide (N3-a) inactivated control cultures. No significant Cr(VI) reduction was observed in the controls. This study is part of the continuing research to identify synergistic culture systems for treating toxic compounds from polluted environments. [ABSTRACT FROM AUTHOR]

A novel biosorbent was prepared by chemically grafting of polyethylenimine (PEI) onto the fungal biomass of Penicillium chrysogenum through a two-step reaction. The modified biosorbent is favorable for the removal of anionic Cr(VI) species from aqueous solution due to the protonation of amine groups on the biomass surface. The sorption capacity for Cr(VI) increased by 7.2-fold after surface modification. Sorption kinetics results show that the pseudo-second order kinetic model described the experimental data well. During the sorption process, X-ray photoelectron spectroscopy (XPS) was used to analyze the chromium species on the biosorbent surface and the results indicate that part of the Cr(VI) ions were reduced to Cr(III) ions which can be chelated with the amine groups on the biomass surface. The reduced Cr(III) ions formed some aggregates on the surface at higher solution pHs. [ABSTRACT FROM AUTHOR]

Two chromate-resistant filamentous fungi, strains H13 and Ed8, were selected from seven independent fungal isolates indigenous to Cr(VI)-contaminated soil because of their ability to decrease hexavalent chromium levels in the growth medium. Morphophysiological studies identified strain H13 as a Penicillium sp. isolate and Ed8 as an Aspergillus sp. isolate. When incubated in minimal medium with glucose as a carbon source and in the presence of 50 µg/mL Cr(VI), these strains caused complete disappearance of Cr(VI) in the growth medium after about 72 h of incubation. Total chromium concentration in growth medium was constant during culture growth, and no accumulation of chromium in fungal biomass was observed. Quantitative determinations of oxidized and reduced chromium species during the reduction process revealed stoichiometric conversion of Cr(VI) to Cr(III). A decrease in Cr(VI) levels from industrial wastes was also induced by Ed8 or H13 biomass. These results indicate that chromate-resistant filamentous fungi with Cr(VI)-reducing capability could be useful for the removal of Cr(VI) contamination. [ABSTRACT FROM AUTHOR]

Abstract: The removal of trivalent chromium from a combined tannery effluent in horizontal settling tanks and subsequent Advanced Integrated Wastewater Pond System (AIWPS) reactors was investigated. The raw combined effluent from Modjo tannery had pH in the range of 11.2–12. At this pH, a trivalent chromium removal of 46–72% was obtained in the horizontal settling tanks after a one-day detention time. Trivalent chromium precipitated as chromium hydroxide, Cr(OH)3. 58–95% Cr(III) was removed in the advanced facultative pond (AFP) where the water column pH of 7.2–8.4 was close to pH 8, which is the optimum precipitation pH for trivalent chromium. Chromium removals in the secondary facultative pond (SFP) and maturation pond (MP) were 30–50% and 6–16%, respectively. With Cr(III) concentration of 0.2–0.8mg/l in the final treated effluent, the AIWPS preceded by horizontal settling tanks produced effluent that could easily meet most of the current Cr(III) discharge limits to receive water bodies. [Copyright &y& Elsevier]

A transient-state model was developed to simulate simultaneous Cr(VI) reduction and phenol degradation by a coculture of Cr(VI)-reducing/phenol-degrading bacteria growing on glass bead surfaces in a fixed-film bioreactor. The coculture consisted of the Cr(VI) reducers, Escherichia coli ATCC 33456, and the phenol degraders, Pseudomonas putida DMP-1. Phenol was supplied as the sole added carbon source and electron donor. The model simulated cell growth kinetics with E. coli utilizing metabolites formed from phenol degradation in P. putida as carbon sources. Substrate utilization and Cr(VI) reduction in the fixed-film bioreactor was 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 by the second-order Crank–Nicholson and backward Euler methods. A heuristic procedure, genetic search algorithm, was used to optimize the model against experimental data. The model predicted effluent concentration with 98.6% confidence for Cr(VI), 93.4% confidence for phenol, and 88.3% confidence for metabolites. Parameters determined showed higher Cr(VI) and phenol removal kinetics in the biofilm system than previously observed in batch systems. [ABSTRACT FROM AUTHOR]

Eleven columns were set up under various groundwater geochemistry conditions to investigate the competitive effect of trichloroethylene (TCE) on hexavalent chromium [Cr(VI)] removal by zero-valent iron (Fe0). They were found to be electron competitors in the redox reactions. In the presence of TCE, the Cr(VI) removal capacities of Fe0 were decreased by about 40% when compared with their respective Cr(VI) removal capacities with identical groundwater geochemistry but without TCE. The specific reaction rate constant (kSA) of TCE was decreased by about 50% when Cr(VI) was singly applied. The kSA of TCE was further decreased by 75% in the presence of both Cr(VI) and carbonate. However, there was no apparent effect on the kSA of TCE when Cr(VI), hardness and carbonate were all present. It revealed that TCE was a stronger electron competitor of Cr(VI) and the degradation of TCE became more favorable when both hardness and carbonate were present. This suggests that the passivated precipitates formed on the Fe0 surface in the presence of both hardness and carbonate may significantly affect the Cr(VI) removal by Fe0 but has insignificant effect on the TCE removal. [ABSTRACT FROM AUTHOR]

In this work, experiments in a 16 L operating volume laboratory pilot plant with ring iron rotary electrodes were performed, obtaining an overall kinetic equation rate of hexavalent chromium reduction concentration and current density-dependent. Other scale-up criteria such as Reynolds' number were also evaluated to ensure a completely stirred reactor at low energy expenditure. A dimensionless NE is a relationship between liquid properties and the electric charge supplied to the system. The number, which depends on the rotation iron ring electrode speed number and the current density, is proposed to be used as scale-up criterion. It was found that at NRe = 42,179 (130 rpm rotation electrodes rate) and at NE = 9.8 x 105 (current density of 113 A/m²), complete mixing was reached at minimum energy spent and the process becomes more efficient. In addition, it was found that the higher the current density, the less treatment time and less energy spent on agitation. After the electrochemical treatment the CrVI concentration in the rinsing wastewater was less than 0.5 mg/L. [ABSTRACT FROM AUTHOR]

A horizontal subsurface flow reed bed, Pragmites australis, constructed wetland system was operated continuously for one year at 5 different hydraulic retention times between 5 days-11 days with real tannery industry effluent to investigate mainly NH4-N and COD removal performance of the system. The bed was also operated at different initial NH4-N concentrations between 10-30 mg/L by adding NH4Cl into the tannery effluent. The results indicated that ammonia-nitrogen removal is significantly affected by hydraulic retention time while COD is not. The optimum HRT was determined as 8 days with over 95% NH4-N and around 30% COD removal efficiency. The system shows higher removal performance at high initial NH4-N concentrations. Almost complete (99%) NH4-N removal and over 40% COD removal was obtained at (NH4-N)0 = 20 mg/L and HRT = 7 days. PO4-P and total chromium removal were not significantly affected by operating conditions [ABSTRACT FROM AUTHOR]

Cr(VI) removal from water was evaluated using waste iron particles in batch experimental mode. The reaction rates were inversely proportional to the initial Cr(VI) concentrations, and the reaction rates of Cr(VI) removal with the waste iron metal were faster than those with Peerless iron, a commercial zero-valent iron. The loss in iron reactivity due to the oxidation, from Fe(0) to Fe(II), ultimately to Fe(III), could be recovered by adding iron-reducing consortium (IRC) to the oxidized iron. Bacterial reduction of Cr(VI) also helped to decrease the aqueous concentration of Cr(VI), but the reduction of oxidized iron by IRC and the consequent reduction of Cr(VI) to Cr(III) by the reduced iron was more significant. Thus, reusing waste iron metal for Cr(VI) removal can reduce the cost of reactive media. Furthermore, the addition of IRC to the waste iron metal can accelerate the removal rate of Cr(VI), and can recover the reactivity of irons which were oxidized by Cr(VI). [Copyright &y& Elsevier]

A bacterial consortium with representatives of sulfate-reducing and denitrifying bacteria was selectively enriched. Model experiments under microaerobic conditions showed that it precipitated chromium from Cr (VI)-containing waters (area of a former electroplating factory, Leipzig, Germany) by two different mechanisms: by sulfate reduction and precipitation as sulfide, and by some direct reduction. Sulfate reduction needed fatty acids as organic substrates and resulted at the first stage in no sulfide accumulation. In the absence of the fatty acids but with straw as organic substrate, the direct reduction of chromium was observed without sulfate reduction. In this case Cr (VI)-reduction rate correlated with that of the denitrification. [Copyright &y& Elsevier]

The effect of hexavalent chromium, Cr(VI), on the maximum specific growth rate, μm and biomass yield, YH, of heterotrophic biomass was studied in batch tests conducted under high (=10) and low (=1.5) substrate-to-biomass ratios (S0/X0). The effects of sludge age and biomass acclimatization to Cr(VI) on the bacterial kinetics were also studied. The μm values were determined by measuring oxygen uptake rate (OUR) and volatile suspended solids (VSS) increase. Cr(VI) concentrations equal or greater than 10 mg l-1 inhibited the growth of unacclimatized activated sludge and caused a significant decrease in μm and YH values. The acclimatization of biomass and the selection of a high operating sludge age reduced the inhibitory effect of Cr(VI). At a sludge age of 20 days, Cr(VI) concentrations of <10 mg l-1 stimulated bacterial growth as evidenced by an increase in both the μm and YH values. Determining μm values by OUR and VSS methods, revealed that the presence of Cr(VI) in unacclimatized biomass caused an inhibitory effect mostly on substrate oxidation, while in acclimatized biomass, anabolic pathways were inhibited more. [Copyright &y& Elsevier]

Describes a method developed for removing chromium from alkaline high-level radioactive tank waste. Importance of removing chromium from the wastes; Caustic leaching; Use of ferrate in chromium removal; Concentrations of transuranic elements from the ferrate leachate solutions.

A cellulose-g-poly-(acrylamide-co-sulfonic acid) polymeric bio-adsorbent (CASA) was prepared by grafting copolymerization, and used to adsorb Cr(III) from leather wastewater. The SEM, XRD, FTIR, and XPS results showed that CASA contains many spherical particles and functional groups such as NH 2 , C O, and HSO 3. The adsorption experiments revealed that CASA presented excellent adsorption performance for Cr(III) (274.69 mg/g of max adsorption capacity) from high-salinity wastewater, which was much better than other reported adsorbents with different structures. Meanwhile, adsorption equilibrium could be reached within 10 min due to the introduction of abundant sulfonic acid groups on its surface. In addition, the adsorption process followed the Langmuir adsorption isotherm, and the experimental data conformed to the pseudo-second-order kinetics model. Moreover, the main adsorption mechanisms include chelation, electrostatic interactions, and cation exchange, which provide an important theoretical basis for the removal of toxic inorganic pollutants from leather wastewater. [Display omitted] • Bio-adsorbent was prepared through grafting copolymerization. • Adsorbent showed better Cr(III) removal from high-salt solution than water samples. • The sulfonated bio-adsorbent could reach adsorption equilibrium within 10 min. • The adsorption capacity reached 274.69 mg/g and mechanism was further discussed. [ABSTRACT FROM AUTHOR]

A restoration strategy was developed for the treatment of two artificial liquid systems (Minimal Medium, MM, and Water Carbon Nitrogen, WCN) contaminated with Cr(VI), lindane (γ-HCH), phenanthrene (Phe), and reactive black 5 (RB5), through the use of an actinobacteria consortium, coupled with a physicochemical treatment using a column filled with nano-scale zero valent iron particles immobilized on dried Macrocystis pyrifera algae biomass. The Sequential Treatment A (ST A : physicochemical followed by biological method) removed the three organic compounds with different effectiveness; however, it was very ineffective for Cr(VI) removal. The Sequential Treatment B (ST B : biological followed by the physicochemical method) removed the four compounds with variable efficiencies. The removal of γ-HCH, Phe, and RB5 in both effluents did not present significant differences, regardless of the sequential treatment used. The highest removal of Cr(VI) and total Cr was observed in MM and WCN, respectively. Ecotoxicity tests (L. sativa) of the effluents treated with both methodological couplings demonstrated that the toxicity of WCN only decreased at the end of ST A , while that of MM decreased at all stages of both sequential treatments. Therefore, MM would be more appropriate to perform both treatments. [Display omitted] • Remediation was studied by coupling microbial and physicochemical treatments. • A versatile restoration strategy for treatment of co-contaminated systems was developed. • Physicochemical followed by biological treatment removed organic pollutants. • Biological followed by physicochemical method removed organic and inorganic pollutants. • Ecotoxicity tests of the treated effluents confirm the decrease in their toxicity. [ABSTRACT FROM AUTHOR]

Hexavalent Chromium (Cr(VI)) has long been known to be highly mobile and toxic when compared with the other stable oxidation state, Cr(III). Cr(VI)-soluble environmental pollutants have been detected in soils and water bodies receiving industrial and agricultural waste. The reduction of Cr(VI) by microbial organisms is considered to be an environmentally compatible, less expensive and sustainable remediation alternative when compared to conventional treatment methods, such as chemical neutralization and chemical precipitation of Cr. This study aims to isolate and identify the composition of the microbial consortium culture isolated from waste activated sludge and digested sludge from a local wastewater treatment plant receiving high loads of Cr(VI) from an abandoned chrome foundry in Brits (North Waste Province, South Africa). Furthermore, the Cr(VI) reduction capability and efficiency by the isolated bacteria were investigated under a range of operational conditions, i.e., pH, temperature and Cr(VI) loading. The culture showed great efficiency in reduction capability, with 100% removal in less than 4 h at a nominal loading concentration of 50 mg Cr(VI)/L. The culture showed resilience by achieving total removal at concentrations as high as 400 mg Cr(VI)/L. The consortia exhibited considerable Cr(VI) removal efficiency in the pH range from 2 to 11, with 100% removal being achieved at a pH value of 7 at a 37 ± 1 °C incubation temperature. The time course reduction data fitted well on both first and second-order exponential rate equation yielding first-order rate constants in the range 0.615 to 0.011 h−1 and second order rate constants 0.0532 to 5 × 10−5 L·mg−1·h−1 for Cr(VI) concentration of 50–400 mg/L. This study demonstrated the bacterial consortium from municipal wastewater sludge has a high tolerance and reduction ability over a wide range of experimental conditions. Thus, show promise that bacteria could be used for hexavalent chromium remediate in contaminated sites. [ABSTRACT FROM AUTHOR]

In the current work we discuss the processes occurring along with the temperature treatment of the samples of chromium containing sludge. The results of powder X-ray diffraction and vibrational magnetometry show that magnetite forms in the samples with the increase of the calcination temperature higher than 500 °C. Its quantity increases with the heating, which is clearly visible from the value of saturation magnetization obtained for the samples after various temperature treatments. [ABSTRACT FROM AUTHOR]

A novel chitosan/grafted halloysitenanotubes@Znγmagnetite quaternary nanocomposite (Ch/g-HNTs@ZnγM) was fabricated using the chemical co-precipitation method to remove the ions of Cr (III), Fe (III), and Mn (II) from wastewater. The characteristics of the synthesized Ch/g-HNTs@ZnγM quaternary nanocomposite were investigated using FTIR, SEM, XRD, GPC, TGA, TEM, and surface zeta potential. The characterization analysis proved that the mentioned nanocomposite structure contains multiple functional groups with variable efficiencies. Additionally, they proved the existence of magnetic iron in the nanocomposite internal structure with the clarity of presentation of gaps and holes of high electron density on its surface. The results showed that the pH and time to reach an equilibrium system for all the studied metal ions were obtained at 9.0 and 60 min, respectively. The synthesized Ch/g-HNTs@ZnγM nanocomposite exhibited maximum adsorption removal of 95.2%, 99.06%, and 87.1% for Cr (III), Fe (III), and Mn (II) ions, respectively. The pseudo-second-order kinetic model and, for isotherm, the Langmuir model were best fitted with the experimental data. The thermodynamic parameters indicated the exothermic and spontaneous nature of the adsorption reaction as proven by the ΔH° and ΔG° values. Additionally, chemical adsorption by the coordination bond is supposed as the main mechanism of adsorption of the mentioned metal ions on the nanocomposite. Finally, Ch/g-HNTs@ZnγM displays prospected advantages, such as a low-expense adsorbent, high efficiency and availability, and an eco-friendly source, that will reduce the environmental load via an environmentally friendly method. [ABSTRACT FROM AUTHOR]

Evaluates the possible hazardous effects of tannery waste and sewage sludge application to the terrestrial environment. Chromium as pollutant in the terrestrial ecosystem; Focus on the determination of hexavalent chromium; Factors for the extent of chromium oxidation; Disposal of chromium-rich waste as a main environmental problem of the leather industry.

Studies the feasibility of utilizing iron-coated spent catalyst to adsorb chromium from aqueous solution. Adsorption of chromium onto iron-coated spent catalyst; Interference of anions on the adsorption; Zeta potential of colloidal systems.

Examines the process of chromium removal and recovery from chrome tan wastewater produced by chrome tanning operation. Characteristics of chromium removal at different slow mixing times; Impact of hydrogen-ion concentration and lime doses on the chromium removal efficiency; Effects of chromium concentration variation on chromium removal efficiency.

Wastewater generated from an industrial estate accommodating chrome as well as vegetable tanneries has a significant pollution potential with COD ranging from as low as 2000 mg/L to as high as 10,000 mg/L. This medium strength wastewater, if segregated from soak liquor and subjected to chromium removal/recovery, can very well be treated anaerobically with recourse to energy recovery. However, this anaerobic treatment is not sufficient and the post-anaerobic effluent requires further aerobic treatment to make the wastewater quality conformatory to ISI norms for inland water disposal. Bench scale studies were carried out on treated tannery effluent from a bench scale anaerobic fixed film fixed bed reactor to evaluate the feasibility of further treatment by the activated sludge process. This paper reports the experimental results of the studies and also highlights the performance evaluation and determination of kinetic constants for the ASP unit. [ABSTRACT FROM AUTHOR]

The article presents a study on the bioremediation of chromium-contained tannery effluent by aquatic macrophytes including Spirodela Rolyrrhiza, Bacopa monnieri, and Hydrilla verticillata. The study used a tannery effluent treated with the macrophytes and 2380 atomic absorption spectrophotometer from Perkin-Elmer Corp. was used in analyzing digested effluent and chromium concentration. Results showed that chromium levels were lessened by the three macrophytes, except S. polyrrhiza.

The present study refers to the use of an environmental pollutant generated during the removal of hexavalent chromium from aqueous media. This pollutant is a material with catalytic properties suitable for application in the oxidative degradation of problematic organic compounds. The material, initially used as an adsorbent, is a composite prepared by modifying the crystalline phases of iron oxides together with the chitosan (CT-FeCr). Chemical and morphological characterizations of the materials were performed using SEM analysis coupled with EDS, XRD and DSC. The CT-FeCr beads were used in the degradation of methylene blue dye (MB) and showed excellent degradation potential (93.6%). The presence of Cr on the surface of the catalyst was responsible for the increase in catalytic activity compared to the CT-Fe and pure magnetite materials. The product of the effluent treatment and the presence of the catalyst itself in the environment do not pose toxic effects. In addition, the CT-FeCr beads showed catalytic stability for several consecutive reaction cycles with possible technical and economic viability. The concept of "industrial symbiosis" may be applied to this technology, with that term relating to the reuse of a byproduct generated in one particular industrial sector by another as a raw material. [ABSTRACT FROM AUTHOR]

The removal of chromium (Cr) from wastewater by various adsorbents has been investigated. As compared with the commercial activated carbon, the biosorbents with inexpensive and high adsorption capacities are developed from lignocellulosic wastes. Lignin, existing in lignocellulosic biomass, is the second most abundant resource in nature. Recently, lignin-based bio-sorbents were served as an advanced novel material for the metal ions and dye adsorption from wastewater. It has showed several advantages in the wastewater treatments because of the low-cost, high adsorption capacity, easy recover, and possibility of metal recovery. In this review, the isolation of lignin from lignocellulosic biomass was summarized, and the structural characteristics of lignin were comparably analyzed. The modification of lignin was performed to obtain a large surface area, strong binding-site, and high and quick adsorption properties of lignin-based adsorption materials. The adsorption efficiency of Cr ions was found to be strongly dependent on the pH of the wastewater. To further illustrate the adsorption process, the structural changes and the interactions between the metal ions and the functional groups of the lignin-based biosorbents in the adsorption process should be further investigated. Once the cost-effective and high-efficiency modification techniques are developed, lignin-based adsorbents can be expected to be the most suitable alternatives for Cr ions removal from wastewater in industry. Fractionational and structural characterization of lignin and its modification as biosorbents for efficient removal of chromium from wastewater. [ABSTRACT FROM AUTHOR]

The hollow polyaniline (PANI) micro/nanospheres are obtained through a simple monomer polymerization in alkaline solution with Triton X-100 Micelles as soft templates. The hollow PANI micro/nanospheres demonstrate rapid and effective removal ability for Chromium (VI) (Cr (VI)) in a wide pH range, and the maximum removal capacity can reach 127.88 mg/g at pH 3. After treated with acid, the used hollow PANI micro/nanospheres have about the similar removal capacity of Cr (VI) from wastewater. [ABSTRACT FROM AUTHOR]

A novel bio-adsorbent was fabricated via grafting an amino-terminated hyperbranched polymer (HBP-NH2) onto bagasse cellulose. The morphology and microstructure of the HBP-NH2-grafted bagasse cellulose (HBP-g-BC) were characterized and its adsorption capacity for Cr(VI) ions in aqueous solutions was investigated. The rough surface structure of HBP-g-BC that is beneficial for improving the adsorption capacity was observed by scanning electron microscopy (SEM). The grafting reaction was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The adsorbent performance was shown to be better with a lower pH value, a higher adsorbent dosage, or a higher initial Cr(VI) concentration. Moreover, the kinetics study revealed that the adsorption behavior followed a pseudo-second-order model. The isotherm results showed that the adsorption data could be well-fitted by the Langmuir, Freundlich, or Temkin models. Moreover, HBP-g-BC could maintain 74.4% of the initial removal rate even after five cycles of regeneration. Thus, the high potential of HBP-g-BC as a bio-adsorbent for heavy metal removal has been demonstrated. [ABSTRACT FROM AUTHOR]

To remove chromium from wastewater effectively, two types of nitrogen-containing fabric adsorbents, having amidoxime ligand groups and quaternary ammonium anion exchange groups, respectively, were prepared by radiation grafting. In brief, the amidoxime adsorbent is obtained by grafting of acrylonitrile (AN)/methacrylic acid (MAA) onto a nonwoven fabric and subsequent amidoximation with hydroxylamine, while the ammonium adsorbent is obtained by grafting of chloromethylstyrene (CMS) followed by quaternization with trimethylamine. The AN/MAA-grafting reaches a high degree of grafting more than 100%, and the resulting amidoxime adsorbent reaches a high amidoxime density of 4.53 mmol/g. On the other hand, the CMS-grafting reaches a much higher degree of grafting above 200%, and the resulting ammonium adsorbent reaches a high ammonium density of 3.51 mmol/g. FTIR/ATR and TGA/DTA are used for the characterization of the grafted fabrics as well as the relevant fabric adsorbents. Furthermore, the chromium removal of the prepared fabric adsorbent is tested in both batch and column modes. It has been confirmed that the chromium removal was largely dependent on the pH of the solution. At pH 5.0, the amidoxime adsorbent shows a high Cr(III) adsorption capacity of 31.68 mg/g, while the ammonium adsorbent shows a much higher Cr(VI) adsorption capacity of 130.65 mg/g. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate some advantages and potential risks of application of sewage sludge from the Municipal Wastewater Treatment Plant in Sokółka to urban soils. The sewage sludge used in the research was free of Salmonella and viable helminth ova--Ascaris sp., Trichuris sp., Toxocara sp. The study also included the determination of concentrations of Cd, Cr, Cu, Mn, Ni, Pb and Zn in soil and in the aboveground parts of lawn grasses and selected physical and chemical properties of soils fertilized with different doses of sludge. The narrow ratio of carbon to nitrogen on test areas provides conditions for rapid decomposition of the organic matter and may cause a gradual release of metals into the soil solution, thus making them more available to the plants. The bioconcentration factor of heavy metals in the plants along the main streets of Białystok is characterized by considerable local variation. Based on these results, it was found that plants absorbed small amounts of Mn, Ni and Pb, while Zn, Cr, Cu and Cd were easily consumed, which may indicate their high mobility. [ABSTRACT FROM AUTHOR]

In this study, an artificial neural network (ANN) based techniques is applied for the prediction of the percentage removal of Cr(VI) ions from aqueous solution using eight different natural biosorbents. The effects of operating parameters such as initial pH, initial Cr(VI) ion concentration, adsorbent dosages, and contact time are studied to optimize the conditions for maximum removal of Cr(VI) ions. The ANN with a single hidden layer trained with Leven- berg-Marquardt algorithm predicted the percentage removal of Cr(VI) ions from aqueous solution accurately. [ABSTRACT FROM AUTHOR]

Chromium is a well-known highly toxic metal, considered as a priority pollutant. In this study, a series of experiments were conducted to investigate the effect of the properties of clay minerals and organic carboxylic acids on the reduction of Cr(VI) in aqueous solution under UV illumination. Two common clay minerals (montmorillonite, kaolinite) and two typical organic carboxylic acids (oxalate and citrate) were utilized in our system. The experimental results confirmed that the existence of oxalate or citrate can markedly accelerate the Cr (VI) photoreduction reaction on the clay minerals in aqueous solution compared with clay minerals alone. This process of photo-reduction follows approximately zero-order kinetics. The effects of pH, dissolved oxygen, and initial Cr(VI) concentration, and clay minerals dose on removal ratio were also investigated. The photoreduction ratio of chromium was favorable under acidic pH than in the weakly alkaline pH. Furthermore, it was found that the dissolved oxygen exerted an inhibition effect on Cr(VI) removal. [ABSTRACT FROM AUTHOR]

Reports on B.T. Nivas and co-workers' development of a method to remediate chromate-contaminated subsurface environments. Characteristic of Cr(VI).