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.     

Bioremediation of Cr(VI) from Chromium-Contaminated Wastewater by Free and Immobilized Cells of Cellulosimicrobium cellulans KUCr3

In this report, possible utilization of a chromium-reducing bacterial strain Cellulosimicrobium cellulans KUCr3 for effective bioremediation of hexavalent chromium (Cr(VI))-containing wastewater fed with tannery effluents has been discussed. Cr(VI) reduction and bioremediation were found to be related to the growth supportive conditions in wastewater, which is indicative of cell mass dependency for Cr(VI) reduction. Cr(VI) reduction was determined by measuring the residual Cr(VI) in the cell-free supernatant using colorimetric reagent S-diphenylcarbazide. Nutrient availability and initial cell density showed a positive relation with Cr(VI) reduction, but it was inhibited with increasing concentration of Cr(VI) under laboratory condition. The optimum temperature and pH for effective Cr(VI) reduction in wastewater were found to be 35°C and 7.5, respectively. The viable cells of KUCr3 were successfully entrapped in an agarose bead that was used in continuous column and batch culture for assaying Cr(VI) reduction. In packed bed column (continuous flow) experiment, approximately 25% Cr(VI) reduction occurred after 144 h. Cr(VI) was almost 75% and 52% reduced at concentrations of 0.5 mM and 2 mM Cr(VI), respectively, after 96 h in batch culture experiment in peptone-yeast extract-glucose medium, whereas it could decrease the Cr(VI) content up to 40% from the water containing tannery waste. This study suggests that KUCr3 could be used as a candidate for possible environmental clean up operation with respect to Cr(VI) bioremediation.     

Hexavalent chromium removal by viable, granular anaerobic biomass

Hexavalent chromium in industrial wastewater is a major concern due to its extreme toxicity. This study investigates the removal of Cr(VI) using viable anaerobic granular biomass as a biosorbent. The effect of Cr(VI) concentration on biogas content and COD removal using batch studies indicated that the phase II (methanogenic-rich) culture was more sensitive than the phase I (acidogenic-rich) culture. Toxicity indices for both cultures using COD removal were developed based on linear-log interpolation. The median inhibition Cr(VI) concentration (IC(50)), for phase II cultures was found to be 263mg/L, while that for phase I cultures was 309mg/L. A sorption study was conducted on viable and non-viable (dried) phase I-rich biomass: both followed the Langmuir model. In addition, the biosorption capacity for metabolically inhibited biomass was 25% less indicating some level of cellular uptake associated with Cr(VI) removal. This study demonstrated the potential for a two-phase anaerobic treatment system for a Cr(VI)-contaminated effluent.     

Removal of hexavalent chromium in tannery wastewater by Bacillus cereus

Bacillus cereus was used to remove chromium (Cr(VI)) from medium containing tannery wastewater under different conditions. The maximum rate of Cr(VI) removal was attained at a temperature of 37?°C, pH of 7.0-9.0, and biomass of 20 g/L when the initial Cr(VI) concentration was less than 50?mg/L. Under the optimum conditions, the Cr(VI) in tannery wastewater was treated with each cellular component of B. cereus to detect its ability to reduce Cr(VI). The results showed that the removal rate of Cr(VI) for the cell-free extracts could reach 92.70%, which was close to that of the whole cells (96.85%), indicating that the Cr(VI) reductase generated by B.?cereus is primarily intracellular. Additionally, during continuous culture of the B. cereus, the strain showed good consecutive growth and removal ability. After treatment of 20?mg/L Cr(VI) for 48?h, the B. cereus was observed by SEM and TEM-EDX. SEM images showed that the B.?cereus used to treat Cr(VI) grew well and had a uniform cellular size. TEM-EDX analysis revealed large quantities of chromium in the B. cereus cells used to treat Cr(VI). Overall, the results presented herein demonstrate that B. cereus can be used as a new biomaterial to remove Cr(VI) from tannery wastewater.     

Efficiency of Penicillium chrysogenum PTCC 5037 in reducing low concentration of chromium hexavalent in a chromium electroplating plant wastewater

The effectiveness of Penicillium chrysogenum was evaluated for reducing Cr(VI) from the wastewater of a chromium electroplating plant. Statistically-based experimental designs were applied to optimize the condition for reducing Cr(VI) to Cr(III). By applying Plackett-Burman factorial design and central composite design as the optimization step, attempts were made to identify optimal values of the three factors that bringing about maximum microorganism activity and therefore maximum hexavalent chromium(VI) bioreduction. It was found that each gram of P. chrysogenum of dry biomass condition could reduce 66 mg of Cr(VI) to Cr(III) in the wastewater of the chromium electroplating plant.     

Treatment of Cr(VI)-containing wastewaters with exopolysaccharide-producing cyanobacteria in pilot flow through and batch systems

Seven exopolysaccharide-producing cyanobacteria were tested with regard to their capability to remove Cr(VI) from the wastewater of a plating industry. The cyanobacterium which showed, under lab conditions, the most promising features with regard to both Cr(VI) removal (about 12 mg of Cr(VI) removed per gram of dry biomass) and growth characteristics (highest growth rate and simplest culture medium) was Nostoc PCC7936. Furthermore, in lab experiments, it was also found that a HCl pretreatment is essential to abate the concentration of Cr(VI) in solution and that the viability of the biomass is not necessary. Subsequently, three pilot devices were tested, one batch (a dialysis cell) and two flow-through systems (a filter press and a column filled with quartz grain). The best performances were obtained with the filter press, where it was observed a sharp decrease in the concentration of Cr(VI), partly due to the adsorption of the metal by the biomass (about 50%) and partly due to its reduction to Cr(III). The results are discussed in terms of the role played by the different components (biomass and polysaccharide) of the cyanobacterial cultures in the removal of Cr(VI).     

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

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

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.     

耐盐菌Staphylococcus sp. YZ-1和Bacillus cereus CC-1的Cr(VI)脱毒特性与机理

[背景]高盐含铬废水的去除过程中,Cr(Ⅵ)还原菌是研究者关注的重点,但目前对耐盐菌株的Cr(Ⅵ)脱毒特性及机理的分析仍较少。[目的]比较两株耐盐菌株的Cr(Ⅵ)移除特性,并区分Cr(Ⅵ)耐受机制的差异;通过基因组测序分析,从基因层面推测铬耐受相关基因;构建铬还原菌的混菌体系,考察两者对去除污染物的协同作用。[方法]从青海茶卡盐湖分离耐盐菌Staphylococcus sp.YZ-1,与Bacillus cereus CC-1进行基础特性和Cr(Ⅵ)去除性能的比较,并通过全基因组序列的分析验证特性测试的结果。[结果]两株菌都具有铬移除特性,但CC-1的铬移除效率更高,在初始Cr(Ⅵ)浓度为0.1 mmol/L情况下,CC-1能在12h内移除95.3%的Cr(Ⅵ),而YZ-1只能移除40.1%。在进一步实验中发现YZ-1只能对Cr(Ⅵ)进行还原,将其转化为可溶的有机态Cr(Ⅲ),而CC-1能同时对Cr(Ⅵ)进行还原和吸附。全基因组分析发现YZ-1具有编码外排泵蛋白的基因和编码NAD(P)H氧化还原酶的基因,而CC-1具有编码铬转运蛋白ChrA和细胞色素C氧化还原酶的基因。两株菌的混菌体系在处理含Cr(Ⅵ)、Te(Ⅳ)的废水时,菌群能将还原产物聚集成团并沉淀到底部。[结论]菌株YZ-1和CC-1均为耐盐铬还原菌,但YZ-1中的铬还原酶为诱导型酶,CC-1则为组成型酶。基因组数据分析鉴别出两者可能同时存在多种铬耐受机制相关编码基因。混合菌群可以结合YZ-1的自絮凝特性和两者均有的Te(Ⅳ)/Cr(Ⅵ)还原活性,具有潜在的实用价值。     

Bioaccumulation and biosorption of chromium by Aspergillus niger MTCC 2594

Chromium toxicity is of prime concern due to chrome tanning processes in the leather sector. Chrome tanning results in the discharge of toxic levels of chromium causing pollution hazards. Chromium levels of Cr(III) and Cr(VI) were high above permissible limits in chrome samples after chrome tanning. The potential of Aspergillus niger MTCC 2594 to accumulate chromium as well as its biosorption capacity is investigated in this study. Bioaccumulation of Cr(III) and Cr(VI) in the spent chrome liquor has resulted in a 75-78% reduction of the initial Cr content in 24-36 h. A. niger biomass is found to be very effective in the biosorption of Cr(III) and Cr(VI) in spent chrome liquor. Maximum adsorption of 83% for biosorption of Cr(III) at 48 h and 79% of Cr(VI) at 36 h in spent chrome liquor is observed. The biosorption characteristics fit well with Langmuir and Freundlich isotherms and the adsorption parameters are evaluated. The biosorption of Cr also follows Lagergren kinetics. A. niger biomass is effectively used for the biosorption of chromium with 79-83% Cr removal in 36-48 h.     

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

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

Reduction of Cr(VI) by immobilized cells of Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776

Hexavalent chromium, a carcinogen and mutagen, can be reduced to Cr(III) by Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776. This study examined Cr(VI) reduction by immobilized cells of the two strains in a common solution matrix using various entrapment matrices. Chitosan and PVA-borate beads did not retain integrity and supported low or no reduction of Cr(VI) by the cells. A commercial preparation (Lentikats) was stable but also did not support Cr(VI) reduction. K-carrageenan beads were stable in batch suspensions but gel integrity was lost after only 5 h in a flow-through system in the presence of 100 microM Cr(VI). The best immobilization matrices were agar and agarose, where the initial rates of reduction of Cr(VI) (from 500 microM solution) for D. vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776 were 127 (agar) and 130 (agarose), and 15 (agar) and 12 (agarose) nmol h(-1) mg dry cell wt(-1), respectively. The higher removal of Cr(VI) by D. vulgaris was also seen in 14-mL packed-bed flow-through columns, where, at a flow rate of 2.4 mL h(-1), the percentage removal of Cr(VI) was approximately 95% and 60% for D. vulgaris and Microbacterium sp., respectively (agar-immobilized cells). The Cr(VI) reducing activities of D. vulgaris and Microbacterium sp. were lost after 159 and 140 h, respectively. Examination of the beads for structural integrity within the columns in situ using magnetic resonance imaging after 24 and 100 h of continuous operation against Cr(VI) (with negligible Cr retained within the columns) showed that agar beads were more stable with time. The most appropriate system for development of a continuous bioprocess is thus the use of D. vulgaris NCIMB 8303 immobilized in an agar gel matrix.     

Effects of low-concentration Cr(VI) on the performance and the membrane fouling of a submerged membrane bioreactor in the treatment of municipal wastewater

The effects of low-concentration Cr(VI) (0.4 mg?l^?1) on the performance of a submerged membrane bioreactor (SMBR) in the treatment of municipal wastewater, as well as membrane fouling were investigated. Compared with the SMBR for control municipal wastewater, the SMBR for Cr(VI)-containing municipal wastewater had a higher concentration of soluble microbial products (SMP) with lower molecular weights, and smaller sludge particle sizes. Furthermore, low-concentration Cr(VI) induced membrane fouling, especially irreversible membrane pore blocking, which markedly shortened the service life of the membrane.     

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.     

Potential of Marine-Derived Fungi to Remove Hexavalent Chromium Pollutant from Culture Broth

Chromium (Cr) released from industrial units such as tanneries, textile and electroplating industries is detrimental to the surrounding ecosystems and human health. The focus of the present study was to check the Cr(VI) removal efficiency by marine-derived fungi from liquid broth. Amongst the three Cr(VI) tolerant isolates, #NIOSN-SK56-S19 (Aspergillus sydowii) showed Cr-removal efficiency of 0.01 mg Cr mg^?1 biomass resulting in 26% abatement of total Cr with just 2.8 mg of biomass produced during the growth in 300 ppm Cr(VI). Scanning Electron Microscopy revealed aggregation of mycelial biomass with exopolysaccharide, while Electron Dispersive Spectroscopy showed the presence of Cr₂O₃ inside the biomass indicating presence of active Cr(VI) removal mechanisms. This was further supported when the Cr(VI) removal was monitored using DPC (1,5-diphenylcarbazide) method. The results of this study point to the potential of marine-derived fungal isolates for Cr(VI) removal.     

A novel technology for biosorption and recovery hexavalent chromium in wastewater by bio-functional magnetic beads

The goal of this study was to develop an applied technique for the removal and recovery of heavy metal in wastewater. It is novel that the Cr(VI) could be adsorbed and recovered by bio-functional magnetic beads. Furthermore, the magnetic separation technology would make their separation more convenient. The beads were constituted by the powder of Rhizopus cohnii and Fe(3)O(4) particles coated with alginate and polyvinyl alcohol (PVA). The parameters effecting Cr(VI) removal were obtained: the optimum pH 1.0 and optimum temperature 28 degrees C. The biosorption took place mainly in form of Cr(VI) and R. cohnii biomass played a key role in Cr(VI) adsorption. The model of Langmuir isotherm and Lagergren could be better used to fit the sorption process and kinetics, respectively. The beads still maintained predominant characteristics of adsorption, recovery and magnetism after five cycles for adsorption-desorption. The mechanism of adsorption was gained by Fourier transform infrared spectroscopy (FTIR), raman spectroscopy (RS) and scanning electron microscopy (SEM). The groups of -NH(3)(+), -NH(2)(+)-, and NH- played an important role in the Cr(VI) adsorption. Consequently, the beads exhibited the superior performances in Cr(VI) cleanup, separation and recovery and the perspective potential in application.     

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.     

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.     

Hexavalent chromium-reducing plant growth-promoting rhizobacteria are utilized to bio-fortify trivalent chromium in fenugreek by promoting plant development and decreasing the toxicity of hexavalent chromium in the soil

BackgroundFenugreek is known to have good anti-diabetes properties. Moreover, several studies accounted that the trivalent form of chromium [Cr(III)] also have anti-diabetic properties. However, its hexavalent form i.e., Cr(VI) is known to be highly toxic and carcinogenic to living beings and retarded plant growth even if it is present in low concentration in soil. Many plant growth-promoting rhizobacteria (PGPR) are reported to have the potential to reduce the Cr(VI) into Cr(III) in soil. In view of the above, the present objective was designed to effectively utilize Cr(VI) reducing PGPRs for the growth and development of fenugreek plant in Cr(VI) amended soil, apart from reducing Cr(VI) in soil and fortification of Cr(III) in the aerial part of plants.MethodsThe experiment was carried out to evaluate the effect of Cr(VI)-reducing PGPRs viz. Bacillus cereus (SUCR44); Microbacterium sp. (SUCR140); Bacillus thuringiensis (SUCR186) and B. subtilis (SUCR188) on growth, uptake and translocation of Cr as well as other physiological parameters in fenugreek grown under artificially Cr(VI) amended soil (100 mg kg⁻¹ of Cr(VI) in soil).ResultsThe aforementioned concentration of Cr(VI) in soil cause severe reduction in root length (41 %), plant height (43 %), dry root (38 %) and herb biomass (48 %), when compared with control negative (CN; uninoculated plant not grown in Cr(VI) contaminated soil). However, the presence of Microbacterium sp.˗SURC140 (MB) mitigates the Cr toxicity resulting in improved root length (92 %), plant height (86 %), dry root (74 %) and herb biomass (99 %) as compared with control positive (CP; uninoculated plants grown in Cr(VI) contaminated soil). The maximum reduction in bioavailability (82 %) of Cr(VI) in soil and its uptake (50 %) by the plant were also observed in MB-treated plants. However, All Cr(VI)-reducing PGPRs failed to decrease the translocation of Cr to the aerial parts. Moreover, the plant treated with MB observed diminution in relative water content (13 %), electrolyte leakage (16%) and lipid peroxidation (38 %) as well as higher chlorophyll (37 %) carotenoids (17 %) contents and antioxidants (18%) potential.ConclusionThis study demonstrates that MB can lower the Cr(VI) toxicity to the plant by reducing the bioavailable Cr(VI), consequently reducing the Cr(VI) toxicity level in soil and helping in improving the growth and yield of fenugreek. Additionally, Cr(III) uptakes and translocation may improve the effectiveness of fenugreek in treating diabetes.     

Biosorption of hexavalent chromium from aqueous solution by a tropical basidiomycete BDT-14 (DSM 15396)

Summary A tropical white-rot basidiomycete, BDT-14 (DSM 15396) was investigated for its chromium (VI) biosorption potential from an aqueous solution. Pre-treatment of fungal biomass with acid resulted in 100% metal adsorption compared to only 26.64% adsorption without any pre-treatment. Chromium adsorption was a rapid process at early exposure resulting in 60% chromium removal within the first 2 h of exposure. An increase in biomass showed an increase in the total metal ions adsorption but a decrease in specific uptake of metal ions. The concentrations of chromium had a pronounced effect on the rate of adsorption. The adsorption efficiency was 100% when the initial Cr (VI) concentration was 100 mg l⁻¹ with 1,000 mg biomass. Only 47.5% adsorption was observed with 500 mg l⁻¹ Cr (VI) concentration. The adsorption data fit well with the Langmuir and Freundlich isotherm models. Comprehensive characterization of parameters indicates BDT−14 biomass as a promising material for Cr (VI) adsorption.