Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.     

Biological decolorization of xanthene dyes by anaerobic granular biomass

Biodegradation of a xanthene dyes was investigated for the first time using anaerobic granular sludge. On a first screening, biomass was able to decolorize, at different extents, six azo dye solutions: acid orange 7, direct black 19, direct blue 71, mordant yellow 10, reactive red 2 and reactive red 120 and two xanthene dyes--Erythrosine B and Eosin Y. Biomass concentration, type of electron donor, induction of biomass with dye and mediation with activated carbon (AC) were variables studied for Erythrosine B (Ery) as model dye. Maximum color removal efficiency was achieved with 4.71 g VSS L?1, while the process rates were independent of the biomass concentration above 1.89 g VSS L?1. No considerable effects were observed when different substrates were used as electron donors (VFA, glucose or lactose). Addition of Ery in the incubation period of biomass led to a fivefold increase of the decolorization rate. The rate of Ery decolorization almost duplicated in the presence of commercial AC (0.1 g L?1 AC?). Using different modified AC samples (from the treatment of AC?), a threefold higher rate was obtained with the most basic one, AC(H?), as compared with non-mediated reaction. Higher rates were obtained at pH 6.0. Chemical reduction using Na?S confirmed the recalcitrant nature of this dye. The results attest that decolorization of Ery is essentially due to enzymatic and adsorption phenomena.     

Hexavalent chromium removal from aqueous solutions by a novel powder prepared from Colocasia esculenta leaves

In this study, batch removal of hexavalent chromium from aqueous solutions by powdered Colocasia esculenta leaves was investigated. Batch experiments were conducted to study the effects of adsorption of Cr(VI) at different pH values, initial concentrations, agitation speeds, temperatures, and contact times. The biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrometer analysis. The biosorptive capacity of the adsorbent was dependent on the pH of the chromium solution in which maximum removal was observed at pH 2. The adsorption equilibrium data were evaluated for various adsorption isotherm models, kinetic models, and thermodynamics. The equilibrium data fitted well with Freundlich and Halsey models. The adsorption capacity calculated was 47.62 mg/g at pH 2. The adsorption kinetic data were best described by pseudo-second-order kinetic model. Thus, Colocasia esculenta leaves can be considered as one of the efficient and cheap biosorbents for hexavalent chromium removal from aqueous solutions.     

Hexavalent chromium reduction by bacteria from tannery effluent

Chromium is generated from several industrial processes. It occurs in different oxidation states, but Cr(III) and Cr(VI) are the most common ones. Cr(VI) is a toxic, soluble environmental contaminant. Some bacteria are able to reduce hexavalent chromium to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of considerable interest. An indigenous chromium-reducing bacterial strain, Rb-2, isolated from a tannery water sample, was identified as Ochrobactrum intermedium, on the basis of 16S rRNA gene sequencing. The influence of factors like temperature of incubation, initial concentration of Cr, mobility of bacteria, and different carbon sources were studied to test the ability of the bacterium to reduce Cr(VI) under variable environmental conditions. The ability of the bacterial strain to reduce hexavalent chromium in artificial and industrial sewage water was evaluated. It was observed that the mechanism of resistance to metal was not due to the change in the permeability barrier of the cell membrane, and the enzyme activity was found to be inductive. Intracellular reduction of Cr(VI) was proven by reductase assay using cell-free extract. Scanning electron microscopy revealed chromium precipitates on bacterial cell surfaces, and transmission electron microscopy showed the outer as well as inner distribution of Cr(VI). This bacterial strain can be useful for Cr(VI) detoxification under a wide range of environmental conditions.     

Hexavalent chromium reduction by an actinomycete, Arthrobacter crystallopoietes ES 32

Environmental contamination by hexavalent chromium, Cr(VI), presents a serious public health problem. This study assessed the reduction of Cr(VI) by intact cells and a cell-free extract (CFE) of an actinomycete, Arthrobacter crystallopoietes (strain ES 32), isolated from soil contaminated with dichromate. Both intact cells and CFE of A. crystallopoietes, displayed substantial reduction of Cr(VI). Intact cells reduced about 90% of the Cr(VI) added within 12 h and Cr(VI) was almost completely reduced after 24 h. The K _M and V _max of Cr(VI) bioreduction by intact cells were 2.61 μM and 0.0142 μmol/min/mg protein, respectively. Cell-free chromate reductase of the A. crystallopoietes (ES 32) reduced hexavalent chromium at a K _M of 1.78 μM and a V _max of 0.096 μmol/min/mg protein. The rate constant (k) of chromate reduction was inversely related to Cr(VI) concentration and the half-life (t _1/2) of Cr(VI) reduction increased with increasing concentration. A. crystallopoietes produced a periplasmic chromate reductase that was stimulated by NADH. Results indicate that A. crystallopoietes ES 32 can be used to detoxify Cr(VI) in polluted sites, particularly in stressed environments.     

Hexavalent chromium: Regulation and health effects

Despite the knowledge about heavy metals toxicity on humans, its use is widely spread mainly for industrial processes. Chromium is an element that belongs to this group and although it is present in our daily diet, it can also be harmful for humans, causing skin allergies and increasing the risk of lung cancer, among other health effects reported. In this review, we highlight its nutritional role, its toxicokinetic and toxicodynamic in humans, its regulation in the industry and the biomonitoring proposal of this element in blood and urine samples with the aim to control the level of exposure of the workers in military industry and also of the general population.     

Hexavalent chromium uptake by sensitive and tolerant mutants of Schizosaccharomyces pombe

Lysine and leucine auxotrophic, heterothallic (h+, h-) strains of Schizosaccharomyces pombe were used to obtain chromium (VI)-sensitive and -tolerant mutants by ultraviolet radiation-induced and nitrosoguanidine-induced mutagenesis. The minimal inhibitory concentrations of K2Cr2O7 on YEA media were 225 microM for the wild-type strain CW-6, 125 microM for the sensitive mutant CS-6.51 and 275 microM for the tolerant mutant CT-6.66. The mutants exhibited cross-sensitivity of various patterns to Cd2+, Cu2+, Ni2+, Zn2+ and VO3-(4). Cr(VI) was added to the actively growing cultures and the total chromium (TOCr) content of the cells was determined. The sensitive mutant exhibited a high bioaccumulation ability, with a dry biomass of 810 micrograms g-1 after 30 min, while the tolerant mutant had a significantly lower ability than the wild-type strain. In PIPES buffer, washed, lysine-starved biomasses were treated with 75 microM Cr(VI) and after 2 h, the TOCr and the organically bound chromium (OBCr) were determined. Under these conditions, the sensitive and tolerant mutants had the same TOCr content, 50% of which was OBCr. The wild-type strain exhibited a lower TOCr content than that of its mutants and only 35% of this was OBCr. The Cr(VI)-sensitivity was due to a significantly increased uptake of Cr(VI).     

Hexavalent chromium removal in vitro and from industrial wastes, using chromate-resistant strains of filamentous fungi indigenous to contaminated wastes

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 microg/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.     

BTEX removal in a horizontal-flow anaerobic immobilized biomass reactor under denitrifying conditions

Because benzene, toluene, ethylbenzene, and xylenes (BTEX) and ethanol are important contaminants present in Brazilian gasoline, it is essential to develop technology that can be used in the bioremediation of gasoline-contaminated aquifers. This paper evaluates the performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor fed with water containing gasoline constituents under denitrifying conditions. Two HAIB reactors filled with polyurethane foam matrices (5 mm cubes, 23 kg/m³ density and 95 % porosity) for biomass attachment were assayed. The reactor fed with synthetic substrate containing protein, carbohydrates, sodium bicarbonate and BTEX solution in ethanol, at an Hydraulic retention time (HRT) of 13.5 h, presented hydrocarbon removal efficiencies of 99 % at the following initial concentrations: benzene 6.7 mg/L, toluene 4.9 mg/L, m-xylene and p-xylene 7.2 mg/L, ethylbenzene 3.7 mg/L, and nitrate 60 mg N/L. The HAIB reactor fed with gasoline-contaminated water at an HRT of 20 h showed hydrocarbon removal efficiencies of 96 % at the following initial concentrations: benzene, 4.9 mg/L; toluene, 7.2 mg/L; m-xylene, 3.7 mg/L; and nitrate 400 mg N/L. Microbiological observations along the length of the HAIB reactor fed with gasoline-contaminated water confirmed that in the first segment of the reactor, denitrifying metabolism predominated, whereas from the first sampling port on, the metabolism observed was predominantly methanogenic.     

Lead removal by Spirulina platensis biomass

In this investigation, we report on the biosorption of Pb (II) from aqueous solutions by the nonliving biomass of the micro-alga (cyanobacterium) Spirulina platensis. Propagation of the micro-alga was carried out in outside oblong raceway ponds. The biomass was cleaned, dried and used for the investigation. The effects of pH, adsorbent dose, temperature, initial concentration of Pb (II), and contact time on the adsorption of lead by the dry biomass were studied. The experiments were carried out in 250 ml conical flasks containing 100 ml of test solutions using an orbital incubator at 150 rpm. Concentrations of the metal before and after the experiments were measured using Atomic Absorption Spectrophotometer. Very high levels of Pb (II) removal (>91%) were obtained. The optimum conditions for maximal adsorption by S. platensis were found to be pH 3; 2 g of adsorbent dose; incubation at 26°C; 100 mg/l of lead initial concentration and 60 minutes of contact time. The experimental data fitted well with Freundlich isotherm equation with R² values greater than 0.97. Based on our results, we recommend the utilization of S. platensis biomass for heavy metal removal from aqueous solutions.     

Simultaneous COD, nitrogen, and phosphate removal by aerobic granular sludge

Aerobic granular sludge technology offers a possibility to design compact wastewater treatment plants based on simultaneous chemical oxygen demand (COD), nitrogen and phosphate removal in one sequencing batch reactor. In earlier studies, it was shown that aerobic granules, cultivated with an aerobic pulse-feeding pattern, were not stable at low dissolved oxygen concentrations. Selection for slow-growing organisms such as phosphate-accumulating organisms (PAO) was shown to be a measure for improved granule stability, particularly at low oxygen concentrations. Moreover, this allows long feeding periods needed for economically feasible full-scale applications. Simultaneous nutrient removal was possible, because of heterotrophic growth inside the granules (denitrifying PAO). At low oxygen saturation (20%) high removal efficiencies were obtained; 100% COD removal, 94% phosphate (P-) removal and 94% total nitrogen (N-) removal (with 100% ammonium removal). Experimental results strongly suggest that P-removal occurs partly by (biologically induced) precipitation. Monitoring the laboratory scale reactors for a long period showed that N-removal efficiency highly depends on the diameter of the granules.     

Hexavalent chromium stimulation of riboflavin synthesis in flavinogenic yeast

Flavinogenic yeast overproduce riboflavin (RF) in iron-deprived media. In optimal growth media supplemented with Fe, hexavalent chromium 'Cr (VI)' treatment led to elevated RF synthesis in all cases of 37 flavinogenic strains studied. The level of RF production exceeded the rate observed at iron-deficient conditions. At sublethal Cr concentrations the RF oversynthesis over time correlated well with the growth-inhibitory adaptational period as manifested by the prolonged lag phase. The consecutive logarithmic biomass growth was accompanied by a drop in RF biosynthesis. Cr (VI)-induced RF overproduction was not a result of cellular iron level decrease. The treatment of yeast with Cr (VI) led to the stimulation of GTP-cyclohydrolase and RF-synthase activities, the key enzymes of the RF biosynthesis pathway.     

Hexavalent chromium disrupts mitosis by stabilizing microtubules in Lens culinaris root tip cells

Hexavalent chromium [Cr(VI)] is an accumulating environmental pollutant due to anthropogenic activities, toxic for humans, animals and plants. Therefore, the effects of Cr(VI) on dividing root cells of lentil (Lens culinaris) were investigated by tubulin immunofluorescence and DNA staining. In Cr(VI)‐treated roots, cell divisions were perturbed, the chromosomes formed irregular aggregations, multinucleate cells were produced and tubulin clusters were entrapped within the nuclei. All cell cycle‐specific microtubule (MT) arrays were affected, indicating a stabilizing effect of Cr(VI) on the MTs of L. culinaris. Besides, a time‐ and concentration‐dependent gradual increase of acetylated α‐tubulin, an indicator of MT stabilization, was observed in Cr(VI)‐treated roots by both immunofluorescence and western blotting. Evidence is also provided that reactive oxygen species (ROS) caused by Cr(VI), determined with the specific marker dichlorofluorescein, may be responsible for MT stabilization. Combined treatments with Cr(VI) and oryzalin revealed that Cr(VI) overcomes the depolymerizing ability of oryzalin, as it does experimentally introduced hydrogen peroxide, further supporting its stabilizing effect. In conclusion, it is suggested that the mitotic aberrations caused by Cr(VI) in L. culinaris root cells may be the result of MT stabilization rather than depolymerization, which consequently disturbs MT dynamics and their related functions.     

Hexavalent chromium reduction by a dichromate-resistant gram-positive bacterium isolated from effluents of tanneries

A gram-positive, chromium (Cr)-resistant bacterial strain (ATCC 700729) was isolated from effluent of tanneries. It was grown in media containing potassium dichromate concentration up to 80 mg ml⁻¹ of the medium. The dichromate reducing capability of the bacterium was checked by estimating the amount of Cr VI in the medium before and after introduction of bacterial culture. The influence of factors like pH of the medium, concentration of Cr, and the amount of the inoculum was studied to determine the ability of the bacterium to reduce Cr VI in the medium under various conditions. In a medium containing dichromate 20 mg ml⁻¹ more than 87% reduction of dichromate ions was achieved within 72 h. The feasibility of the use of this bacterial strain for detoxification of dichromate in the industrial wastewater has been assessed. The isolated strain can be exploited for specific environmental clean-up operations. Received: 7 April 1999 / Accepted: 12 September 1999     

Algal biomass anaerobic biodegradability

We conducted a series of biodegradation studies using microalgae (Arthrospira maxima and Nannochloropsis sp.) and macroalgae (Gelidium corneum and Cladophora glomerata) to elucidate algal biodegradability in wastewater sludge under anaerobic conditions. Algal biodegradability was evaluated according to ASTM D5210-92. The results indicate that A. maxima biodegraded to a greater extent (70 %) than Nannochloropsis sp. (40 %). The low level of mineralization for Nannochloropsis sp. is due to the presence of high level of lipids (37 %). For macroalgal samples, red algae fiber pulped from G. corneum biodegraded comparably to cellulose controls. However, C. glomerata biodegradation is about 46 %. A sample compositional analysis revealed that it contained about 24.5 % ash, which is directly accountable for an observed low degree of biodegradation. Algal anaerobic biodegradability is important to facilitate sludge digester design and performance evaluation. It is particularly useful when waste residual materials from algal biofuel processing are used for energy production.     

传统厌氧/好氧生物除磷与厌氧/缺氧反硝化除磷效能的比较

采用序批式反应器(SBR),对比厌氧/好氧(A/O)和厌氧/缺氧(A/A)2种运行模式对模拟生活和工业混合污水同时脱氮除磷的效能。结果表明:反硝化聚磷菌完全可以在厌氧/缺氧交替运行条件下得到富集,稳定运行的2种模式对有机物和P的去除率分别保持在90%和85%以上,且A/A SBR具有更强的释磷能力,其释磷量比A/O SBR高出1.2倍。进一步试验表明:磷的释放在有无硝酸盐的情况下效果是不同的。2个系统内污泥均有反硝化除磷能力,A/A SBR中所含反硝化聚磷菌(DPAO)的比例是A/O SBR的4.56倍。2种模式出水水质都能取得较好的效果,且能实现同步除磷脱氮,而反硝化除磷在生物除磷方面更具优势。     

Hexavalent chromium reduction by bacterial consortia and pure strains from an alkaline industrial effluent

Aims: To characterize the bacterial consortia and isolates selected for their role in hexavalent chromium removal by adsorption and reduction. Methods and Results: Bacterial consortia from industrial wastes revealed significant Cr(VI) removal after 15 days when incubated in medium M9 at pH 6·5 and 8·0. The results suggested chromium reduction. The bacterial consortia diversity (T‐RFLP based on 16S rRNA gene) indicated a highest number of operational taxonomic units in an alkaline carbonate medium mimicking in situ conditions. However, incubations under such conditions revealed low Cr(VI) removal. Genomic libraries were obtained for the consortia exhibiting optimal Cr(VI) removal (M9 medium at pH 6·5 and 8·0). They revealed the dominance of 16S rRNA gene sequences related to the genera Pseudomonas/Stenotrophomonas or Enterobacter/Halomonas, respectively. Isolates related to Pseudomonas fluorescens and Enterobacter aerogenes were efficient in Cr(VI) reduction and adsorption to the biomass. Conclusions: Cr(VI) reduction was better at neutral pH rather than under in situ conditions (alkaline pH with carbonate). Isolated strains exhibited significant capacity for Cr(VI) reduction and adsorption. Significance and Impact of Study: Bacterial communities from chromium‐contaminated industrial wastes as well as isolates were able to remove Cr(VI). The results suggest a good potential for bioremediation of industrial wastes when optimal conditions are applied.     

PPCPs removal by aerobic granular sludge membrane bioreactor

An aerobic granular sludge membrane bioreactor (GMBR) was applied to the treatment of pharmaceutical and personal care products (PPCPs) wastewater. The influence of granular sludge on five antibiotic and antiphlogistic PPCPs wastewater and the removal effect of methyl alcohol and conventional organic matter were investigated while constantly reducing the density of inflow organic matter. The results showed that the sludge granulation process in the system was rapid but unstable, and that the system exhibits a dissolution–reunion dynamic equilibrium. The reactor demonstrated varying removal effects of PPCPs on different objects. The use of a GMBR was more effective for the removal of prednisolone, naproxen, and ibuprofen; the first two drugs were lower the average removal rate of which reached 98.46 and 84.02 %, respectively; whereas the average removal rate of ibuprofen was 63.32 %. By contrast, the GMBR has an insignificant degradation effect on antibiotics such as amoxicillin, indicating that such antibiotic medicine is not easily degraded by microorganisms, which plays different roles in system operation. Because of the different chemical structures and characteristics of drugs that result in various degradation behavior. During the GMBR granulation process, the value of mixed liquor volatility suspended solids (MLVSS) gradually increases from 1.5 to 4.1 g/L during the GMBR granulation process, and the removal rate of COD_Cr reaches up to 87.98 %. After reducing the density of organic matter is reduced, the removal rates of NH₃-N and TP both reach more than 90 %, respectively. Moreover, the proposed technique is considerably effective in the removal of methanol.     

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.