Adsorption of chromium from aqueous solution by activated alumina and activated charcoal

Cr(VI) is considered to be potentially carcinogenic to humans. Removal of Cr(VI) ions from aqueous solution under different conditions was investigated using activated alumina (AA) and activated charcoal (AC) as adsorbents. Batch mode experiments were conducted to study the effects of adsorbent dose, contact time, pH, temperature and initial concentration of Cr(VI). Results showed that the adsorption of Cr(VI) depended significantly on pH and temperature. Equilibrium studies showed that Cr(VI) had a high affinity for AA at pH 4 and AC at pH 2. For AA, maximum adsorption was found at 25 degrees C, indicating exothermic adsorption, while for AC, maximum adsorption was at 40 degrees C. Freundlich and Langmuir adsorption isotherms were also applied and they showed good fits to the experimental data. The results suggest that both AA and AC could be used as effective adsorbents for the removal of Cr(VI) ions.     

Development of a new Cr(VI)-biosorbent from agricultural biowaste

Among useless but abundant agricultural biowastes such as banana skin, green tea waste, oak leaf, walnut shell, peanut shell and rice husk, in this study, banana skin was screened as the most efficient biomaterial to remove toxic Cr(VI) from aqueous solution. X-ray photoelectron spectroscopy (XPS) study revealed that the mechanism of Cr(VI) biosorption by banana skin was its complete reduction into Cr(III) in both aqueous and solid phases and partial binding of the reduced-Cr(III), in the range of pH 1.5-4 tested. One gram of banana skin could reduce 249.6 (+/-4.2)mg of Cr(VI) at initial pH 1.5. Namely, Cr(VI)-reducing capacity of banana skin was four times higher than that of a common chemical Cr(VI)-reductant, FeSO(4).7H(2)O. To diminish undesirable/serious organic leaching from the biomaterial and to enhance removal efficiency of total Cr, its powder was immobilized within Ca-alginate bead. The developed Cr(VI)-biosorbent could completely reduce toxic Cr(VI) to less toxic Cr(III) and could remove almost of the reduced-Cr(III) from aqueous phase. On the basis of removal mechanisms of Cr(VI) and total Cr by the Cr(VI)-biosorbent, a kinetic model was derived and could be successfully used to predict their removal behaviors in aqueous phase. In conclusion, our Cr(VI)-biosorbent must be a potent candidate to substitute for chemical reductants as well as adsorbents for treating Cr(VI)-bearing wastewaters.     

Adsorption of chromium from aqueous solution on treated sawdust

The adsorption of Cr(VI) from aqueous solutions on formaldehyde treated sawdust (SD) and sulphuric acid treated sawdust carbon (SDC) of Indian Rosewood, a timber industry waste, was studied at varying Cr(VI) concentrations, adsorbent dose, pH and agitation time. Similar experiments were conducted with commercially available coconut based activated carbon to compare the results. The Cr(VI) adsorption efficiency on SDC was higher than SD. The adsorption followed first order rate expression and Lagergren equation. An initial pH of 3.0 was most favorable for Cr(VI) removal by both the adsorbents. Maximum Cr(VI) was sequestered from the solution within 60 min after the beginning for every experiment. It is proposed that SDC and SD can be potential adsorbents for Cr(VI) removal from dilute solutions.     

Removal of chromium from industrial waste by using eucalyptus bark

Several low cost biomaterials such as baggase, charred rice husk, activated charcoal and eucalyptus bark (EB) were tested for removal of chromium. All the experiments were carried out in batch process with laboratory prepared samples and wastewater obtained from metal finishing section of auto ancillary unit. The adsorbent, which had highest chromium(VI) removal was EB. Influences of chromium concentration, pH, contact time on removal of chromium from effluent was investigated. The adsorption data were fitted well by Freundlich isotherm. The kinetic data were analyzed by using a first order Lagergren kinetic. The Gibbs free energy was obtained for each system and was found to be -1.879 kJ mol(-1) for Cr(VI) and -3.885 kJ mol(-1) for Cr(III) for removal from industrial effluent. The negative value of deltaG0 indicates the feasibility and spontaneous nature of adsorption. The maximum removal of Cr(VI) was observed at pH 2. Adsorption capacity was found to be 45 mg/g of adsorbent, at Cr(VI) concentration in the effluent being 250 mg/l. A waste water sample containing Cr(VI), Cr(III), Mg, and Ca obtained from industrial unit showed satisfactory removal of chromium. The results indicate that eucalyptus bark can be used for the removal of chromium.     

Effect of organic Cr(III) complexes on chromium speciation

Abstract

Chromium speciation in the presence of organic chromium(III) complexes was investigated using solid-phase extraction. The adsorptions of Cr(VI) and Cr(III) on alumina and pumice powder were studied. Maximum sorption of Cr(VI) was obtained by alumina (90.22%), while Cr(III) was highly adsorbed onto pumice powder (86.65%). This result shows that pumice may be a new and promising adsorbent for Cr(III). The experimental equilibrium data for Cr(VI) adsorption onto alumina and Cr(III) sorption onto pumice were analysed using Langmuir and Freundlich isotherms. The separation and adsorption of Cr(VI), Cr(III) and five organic chromium(III) complexes onto pumice and alumina at different pH values were evaluated. Ethylenediaminetetraacetate (EDTA), oxalate, citrate, glycine, alanine and 8-hydroxyqinoline were used as ligands. Sorption of alanine and ethylenediaminetetraacetate complexes was higher onto alumina than pumice at pH>3. The enhancement of adsorption of chromium(III) complexes onto pumice was achieved by surface modification of pumice using a surfactant, namely hexadecyltrimethylammoniumbromür (HDTMA). The presence of surfactant enhanced the adsorption of Cr(III) citrate, oxalate, glycine and 8-hydroxyquinoline complexes onto pumice. However, the adsorption of EDTA and alanine complexes decreased, with ratio of 13.40% and 4.00% respectively. Here we demonstrate that chromium speciation methods depending on adsorption onto various adsorbents including alumina may lead erroneous results. Analytical measurements were performed by flame AAS, data were obtained by standard addition method.     

Removal of Cr(VI) from aqueous solutions by adsorption onto hazelnut shell activated carbon: kinetic and equilibrium studies

The adsorption Cr(VI) from aqueous solutions onto hazelnut shell activated carbon was carried out by varying the parameters such as pH, initial Cr(VI) concentration and temperature. The experimental data fitted well to the pseudo first-order kinetic model and then the rate constants were evaluated. The Langmuir isotherm provided the best correlation for Cr(VI) onto the activated carbon. Adsorption capacity was calculated from the Langmuir isotherm as 170 mg/g at an initial pH of 1.0 for the 1000 mg/l Cr(VI) solution. Thermodynamic parameters were evaluated and the adsorption is endothermic showing monolayer adsorption of Cr(VI).     

Adsorption of heavy metal ions from aqueous solutions by activated carbon prepared from apricot stone

Apricot stones were carbonised and activated after treatment with sulphuric acid (1:1) at 200 degrees C for 24 h. The ability of the activated carbon to remove Ni(II), Co(II), Cd(II), Cu(II), Pb(II), Cr(III) and Cr(VI) ions from aqueous solutions by adsorption was investigated. Batch adsorption experiments were conducted to observe the effect of pH (1-6) on the activated carbon. The adsorptions of these metals were found to be dependent on solution pH. Highest adsorption occurred at 1-2 for Cr(VI) and 3-6 for the rest of the metal ions, respectively. Adsorption capacities for the metal ions were obtained in the descending order of Cr(VI) > Cd(II) > Co(II) > Cr(III) > Ni(II) > Cu(II) > Pb(II) for the activated carbon prepared from apricot stone (ASAC).     

Column study on the adsorption of Cr(III) and Cr(VI) using Pumice, Yarikkaya brown coal, Chelex-100 and Lewatit MP 62

In the present study, adsorption of Cr(III) and Cr(VI) on Pumice (Pmc), Yarikkaya (YK) brown coal, Chelex-100, and Lewatit MP 62 is examined at room temperature and at initial chromium concentration of 1.0 x 10(-3) mol/L. Column method was carried out as a function of pH, concentration of Cr(III) and Cr(VI) ions, volume of samples and flow rate. The experimental data were evaluated by Freundlich and Langmuir isotherm models. The dynamic breakthrough capacities of the adsorbents for Cr(III) and Cr(VI) were calculated. The maximum chromium sorption occurred at 5 mL/min flow rate and 25 mL volume for all adsorbents. The results showed that the two readily available adsorbents namely Pmc and YK, were suitable for removing chromium from aqueous solution.     

Preliminary studies on continuous chromium(VI) biological removal from wastewater by anaerobic-aerobic activated sludge process

The long-term continuous chromium(VI) removal from synthetic wastewater affected by influent hexavalent chromium (Cr(VI)) and glucose concentrations were studied with an anaerobic-aerobic activated sludge process. It was observed that before activated sludge was acclimated, the chromium in the effluent increased immediately as the influent chromium increased. However, both Cr(VI) and total chromium (TCr) in the effluent significantly decreased after acclimation. In the acclimated activated sludge, the chromium removal efficiency was 100% Cr(VI) and 98.56% TCr at influent Cr(VI) levels of 20 mg/day, 100% Cr(VI) and 98.92% TCr at influent Cr(VI) levels of 40 mg/day, and 98.64% Cr(VI) and 97.16% TCr at influent Cr(VI) levels of 60 mg/day. The corresponding effluent Cr(VI) and TCr concentrations were 0 and 0.012 mg/l, 0 and 0.018 mg/l, and 0.034 mg/l and 0.071 mg/l, respectively. When the influent glucose increased from 1125 to 1500 mg/l at influent Cr(VI) dosage of 60 mg/day, the Cr(VI) and TCr removal efficiency with the acclimated activated sludge improved from 98.64% and 97.16% to 100% and 98.48%, respectively, and the chromium concentration in the effluent decreased from 0.034 mg/l of Cr(VI) and 0.071 mg/l of TCr to 0 (Cr(VI)) and 0.038 mg/l (TCr). The effluent COD and turbidity was around 40 mg/l and 0, respectively, after the activated sludge was acclimated. Further studies showed that after the activated sludge was acclimated, its specific dehydrogenases activity (SDA) and protein contents increased. The SDA and protein increased respectively 15% and 10% when influent Cr(VI) increased from 20 to 60 mg/day.     

Adsorption studies on rice husk: removal and recovery of Cd(II) from wastewater

Adsorption behaviour of Ni(II), Zn(II), Cd(II) and Cr(VI) on untreated and phosphate-treated rice husk (PRH) showed that adsorption of Ni(II) and Cd(II) was greater when PRH was used as an adsorbent. Sorption of Cd(II) was dependent on contact time, concentration, temperature, adsorbent doses and pH of the solution. The Langmuir constants and thermodynamic parameters have been calculated at different temperatures. It was found that recovery of Cd(II) from synthetic wastewater by column operation was better than a batch process.     

Effects of combining biological treatment and activated carbon on hexavalent chromium reduction

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (μ_obs), biomass yield (Y_X/S), and specific growth substrate consumption rate (q_S) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (μ_obs, Y_X/S, q_S). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.     

Use of low-cost biological wastes and vermiculite for removal of chromium from tannery effluent

Biological wastes (sawdust, rice husk, coirpith and charcoal) and a naturally occurring mineral (vermiculite) have been tested for their effectiveness in removing Cr from tannery effluent through batch and column experiments. The adsorption capacities of the substrates were also evaluated using isotherm tests and computing distribution co-efficient. The sawdust exhibited a higher adsorption capacity (k = 1482 mgkg(-1)), followed by coirpith (k = 159 mgkg(-1)). The biosorbent and mineral vermiculite in columns were found very effective in removing Cr from tannery effluent. About 94% removal of Cr was achieved by a column of coirpith, and equally (93%) by a column containing a mixture of coirpith and vermiculite. This study showed that biological wastes are potential adsorbents of Cr, which could be successfully used to reduce the Cr concentrations in tannery effluent.     

Influence of the activated sludge system configuration on heavy metal toxicity reduction

The effect of configuration of activated sludge systems on heavy metal toxicity was investigated. Two bench-scale completely mixed activated sludge systems were operated identically in order to determine the toxic effects of Cr(VI), Zn(II) and industrial wastewater on the activated sludge biomass. One system was operated with an aerobic selector and the other without. Batch experiments based on OECD 209 (Organisation for Economic Cooperation and Development) were performed using a respirometer to find out potential toxicity reduction effect of an aerobic selector. The IC₅₀ (concentration of a chemical that exhibits 50% respiration inhibition) values of Cr(VI), Zn(II) and industrial wastewater in the activated sludge were determined. Results indicated that the heavy metals and industrial wastewater caused less inhibitory effect on the selector activated sludge system in comparison to the conventional activated sludge system. Cr(VI) was found to exert higher inhibition on both systems.     

Production of activated carbon from bagasse and rice husk by a single-stage chemical activation method at low retention times

The production of activated carbon from bagasse and rice husk by a single-stage chemical activation method in short retention times (30-60min) was examined in this study. The raw materials were subjected to a chemical pretreatment and were fed to the reactor in the form of a paste (75% moisture). Chemicals examined were ZnCl2, NaOH and H3PO4, for temperatures of 600, 700 and 800 degrees C. Of the three chemical reagents under evaluation only ZnCl2 produced activated carbons with high surface areas. BET surface areas for rice husk were up to 750m2/g for 1:1 ZnCl2:rice husk ratio. BET surface areas for bagasse were up to 674m2/g for 0.75:1 ZnCl2:bagasse ratio. Results were compared to regular two-stage physical activation methods.     

Effect of hexavalent chromium on the activated sludge process and on the sludge protozoan community

The objectives of this study were the determination of chromium effects to the performance of an activated sludge unit and the investigation of the response of the activated sludge protozoan community to Cr(VI). Two bench scale activated sludge reactors were supplied with synthetic sewage containing Cr(VI), at concentrations from 1 up to 50 mg L(-1). Protozoan species were identified and were related to the system efficiency. Variations in the abundance and diversity of the protozoan species were observed under various chromium concentrations. High removal rates of organics and nutrients were observed after the acclimatization of the activated sludge, which were related to the initial chromium(VI) concentration. Chromium(VI) removal efficiency was high in all cases. The protistan community was affected by the influent chromium content. Dominance of sessile species was observed in the reactor receiving 5 mg L(-1) influent chromium, whereas co-dominance of sessile and carnivorous species was observed in the reactors receiving higher chromium concentrations.     

纳米银复合介孔碳材料制备固定化猪胰脂肪酶

以稻壳为原料制备介孔碳材料,对其表面进行纳米银修饰后作为猪胰脂肪酶(PPL)的固定化载体.初步研究并优化该载体固定猪胰脂肪酶的条件.结果表明:在AgNO3浓度为0.01 mol/L、固载时间6h、反应磷酸盐溶液pH为6.0、反应温度25℃时,可达最大酶活,酶活提高3.2倍.同时利用红外图谱(FT-IR)、N2等温吸附-脱附曲线(BET)和扫描电子显微镜(SEM)的分析手段对固定化猪胰脂肪酶试样进行分析,进一步确定了纳米银复合介孔性碳材料在固定化酶实验中的作用.     

Batch removal of chromium(VI) from aqueous solution by Turkish brown coals

The ability of using low-rank Turkish brown coals (Ilgın: BC₁, Beyşehir: BC₂, and Ermenek: BC₃) to remove Cr(VI) from aqueous solutions was studied as a function of contact time, solution pH, temperature, concentration of metal solutions and amount of adsorbent. Their sorption properties were compared with the activated carbon from Chemviron (AQ-30). Adsorption of Cr(VI) uptake is in all cases pH-dependent showing a maximum at equilibrium pH values between 2.0 and 3.2, depending on the biomaterial, that correspond to initial pH values of 2.3 units for BC₁, 3.0 units for BC₂ and 3.2 units for BC₃ and AQ-30. Batch equilibrium tests showed that the Cr(VI) removal was fitted with Freundlich isotherm and the adsorption reached equilibrium in 80 min. It was proceeding effectively into a short acid pH interval (2.0–3.2) where processes of Cr(VI) sorption are maximized. It was observed that the maximum adsorption capacity of 11.2 mM of Cr(VI)/g for Ilgın (BC₁), 12.4 mM of Cr(VI)/g for Beyşehir (BC₂), 7.4 mM of Cr(VI)/g for Ermenek (BC₃) and 6.8 mM of Cr(VI)/g for activated carbon (AQ-30) was achieved at pH of 3.0. The rise in temperature caused a slight decrease in the value of the equilibrium constant (K_c) for the sorption of Cr(VI) ion. The Cr(VI) sorption capacities of Beyşehir and Ilgın brown coals were the same. Ermenek brown coals and activated carbon (AQ-30) showed a similar sorption capacity.     

Enhanced Immobilization of Cr(VI) in Soils by the Amendment of Rice Straw Char

This study investigated the effect of rice straw char (RSC) on the immobilization of Cr(VI) in soils. The Cr(VI) sorption experiments on the RSC and RSC-amended soils were conducted using the batch method. RSC exhibited Cr(VI) reduction capacity due to its black carbon content. The addition of RSC to the soils enhanced the overall Cr(VI) immobilization of the soils, which is primarily attributed to the Cr(VI) reduction capacity of RSC. The effects of RSC amendment on the Cr(VI) sorption of the soils increased with increasing RSC content in the soils and decreased with increasing pH or anion contents in the soil solutions. After Cr(VI) was sorbed by the soils, a portion of the Cr(VI) was converted to Cr(III) and the remainder was sorbed onto the soils. The presence of RSC in the soils decreased the portion of sorbed Cr(VI) in the soils and therefore lowered the potential remobilization of Cr(VI) from the soils. The results suggested that RSC amendment can be applied to develop a cost-effective method for immobilizing Cr(VI) in polluted soils, thus lowering the environmental risk from Cr(VI) toxicity.     

Short-term batch studies on biological removal of chromium from synthetic wastewater using activated sludge biomass

Biological treatment of Cr(VI)-containing wastewater has drawn much attention recently as a method to treat environmental Cr(VI) contamination. The activated sludge method, due to its convenient operation and easy-to-scale-up, has been widely applied to treat municipal wastewater and some industrial wastewaters. In order to develop a suitable technique using activated sludge as the biomass to continuously remove Cr(VI) from wastewater, this paper investigated in short-term batch experiments the environmental elements affecting chromium biological removal from synthetic wastewater. The dissolved oxygen (DO), Cr(VI) initial concentration, biomass density, temperature, glucose content in the influent and contact time were observed to strongly influence chromium removal. It was found that the chromium removal efficiency decreased with the increase of DO and Cr(VI) initial concentration as well as glucose content in the feed, but increases in temperature and contact time improved the chromium removal efficiency. Although raising biomass concentration resulted in an increased chromium removal efficiency under both anaerobic and aerobic conditions, its influence on specific chromium removal was not significant.     

Diversity of chromium-resistant and -reducing bacteria in a chromium-contaminated activated sludge

AIMS: This study attempts to establish a relationship between the Cr(VI) resistance of the culturable microbial community and the Cr(VI) resistance and Cr(VI)-reducing ability of representative strains of each population, in order to assess whether these are exclusive characteristics of one microbial group or abilities shared among many groups. METHODS AND RESULTS: A group of 48 Cr(VI)-resistant isolates, with different colony types, was isolated from chromium-contaminated activated sludge. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis protein patterns and fatty acid methyl ester analysis identified six populations, representing 54% of the isolated bacteria, as belonging to the genera Acinetobacter and Ochrobactrum. The remaining populations included strains identified as species of the beta-Proteobacteria and high G + C Gram-positive bacteria. The Cr(VI) resistance and reduction ability of the strains were tested. All but two isolates grew in the presence of 1 mmol l(-1) Cr(VI). During enrichment, all isolates were able to survive to 2 mmol l(-1) Cr(VI) and complete Cr(VI) reduction was achieved. Representative strains of each population were able to partially reduce (5.4-39.1%) the Cr(VI) present in the growth medium. CONCLUSIONS: Most of the identified isolates have never been reported to be Cr(VI)-resistant and/or Cr(VI)-reducing strains. The mechanisms of Cr(VI) resistance and reduction may differ from group to group; therefore, it is evident that both Cr(VI) resistance and reduction are shared abilities and not an exclusive characteristic of a single group, possibly reflecting horizontal genetic transfer resulting from selective pressure in this contaminated environment. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first study of a microbial community under chronic chromate stress and, as the success of microbial-based metal remediation technologies requires a better understanding of the microbial community and the population response to metal stress, it may contribute to the implementation of a strategy of bioremediation of chromate-contaminated environments.