Application of a hybrid biofilter column for the removal of Cr(VI) from aqueous solution using an indigenous bacterial strain Pseudomonas taiwanensis

In the present study, a laboratory-scale biofilter column was designed and fabricated. It was packed with a mixture of coal and compost as a packing medium. The column was enriched with an indigenous bacterial strain Pseudomonas taiwanensis isolated from aerobic mixed culture of Sewage Treatment Plant, BITS-Pilani, Pilani campus. The removal of hexavalent chromium [Cr(VI)] from aqueous solution was investigated in the biofilter column. The entire biofiltration operation was divided into five phases (I to V) for a period of 63 days. Biofilter column was subjected to shock loading conditions for 20 days immediately after 63 days of operation. The maximum removal efficiency of 89.4% was obtained during phase V for Cr(VI) inlet concentration of 40 mg L^?1. During shock loading, maximum removal efficiency was obtained as 90% for 48.5–50 mg L^?1 of initial Cr(VI) concentration. Kinetic parameters of biofiltration process for Cr(VI) removal were also determined by fitting Michaelis-Menten kinetic model with experimental data. The Michaelis-Menten kinetic constants were obtained as 0.258 mg L^?1 min^?1 and 26.83 mg L^?1. It was found that Ottengraf-Van den Oever model with zero-order diffusion limitation fit the experimental data quite well for phases III, IV, and V with coefficient of determination (R²) values .97, .99, and .984, respectively. A possible method for safe disposal of packing medium was also presented in this study.     

Cr(III) Oxidation and Cr Toxicity in Cultures of the Manganese(II)-Oxidizing Pseudomonas putida Strain GB-1

Abstract

Mn oxides have long been considered the primary environmental oxidant of Cr(III), however, since most of the reactive Mn oxides in the environment are believed to be of biological origin, microorganisms may indirectly mediate Cr(III) oxidation and accelerate the rate over that seen in purely abiotic systems. In this study, we examined the ability of the Mn(II)-oxidizing bacterium, Pseudomonas putida strain GB-1, to oxidize Cr(III). Our results show that GB-1 cannot oxidize Cr(III) directly, but that in the presence of Mn(II), Cr(III) can be rapidly and completely oxidized. Growth studies suggest that in growth medium with few organics the resulting Cr(VI) may be less toxic to P. putida GB-1 than Cr(III), which is generally considered less hazardous. In addition, Cr(III) present during the growth of P. putida GB-1 appeared to cause iron stress as determined by the production of the fluorescent siderophore pyoverdine. When stressed by Fe limitation or Cr(III) toxicity, Mn(II) oxidation by GB-1 is inhibited.     

Optimization of Chromium(VI) Detoxification by Pseudomonas aeruginosa and Its Application for Treatment of Industrial Waste and Contaminated Soil

The reduction of Cr(VI) to Cr(III) is a potential detoxification process. In this study, seven Pseudomonas spp. were isolated and screened for chromium reduction. Isolate P4 was able to grow in the presence of 8000 μM chromium, in spite of the fact that the isolate was not previously exposed to any metal stress. Isolate P4 was identified as Pseudomonas aeruginosa strain SRD chr3 by 16S rDNA sequence analysis. Shake flask study showed 78% reduction of 1000 μM Cr(VI) after 6 h of incubation. The optimum pH for chromium reduction by the isolate was between 6 and 8. Isolate Pseudomonas aeruginosa gave 50–80% Cr(VI) reduction even in the presence of 100 mM of Cu, Mn, Ni, and Zn and 300–800 mM NaCl in 24 h, compared with the absence of any of these metals. In a 5-L reactor, the isolate showed 84.85% reduction of Cr(VI) even at the 70th cycle, with a hydraulic retention time of 24 h from the effluent of a hard chrome plating (electroplating) industry, which contained 2100 mg L^?1 hexavalent chromium. The chromate-amended soil inoculated with the isolate showed 2800 μM chromium removal from 4000 μM Cr(VI) kg^?1 of soil, which corresponds to 70% removal. The isolate had the ability to degrade stimulated waste containing 10,000 μM chromium.     

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.     

一株李氏禾内生细菌去除Cr(Ⅵ)的特性

李氏禾(Leersia hexandra)是中国境内发现的第一种铬超积累植物,该文对李氏禾内生菌及其除铬性能进行了研究。采用添加Cr(VI)的牛肉膏蛋白胨固体平板培养方法,从李氏禾根部分离筛选获得一株具有较强Cr(VI)抗性的内生细菌G04,分子生物学鉴定结果表明该菌株属于阴沟肠杆菌(Enterobacter cloacae)。采用摇瓶培养方法,以Cr(VI)去除率、总Cr(铬)的去除率以及菌体生物量为指标,考察了pH、温度、底物浓度、装液量、接种量、摇床转速以及反应时间等因素对Cr(VI)去除率、总铬去除率和菌株生长的影响。结果表明:在牛肉膏蛋白胨液体培养基中,菌株E. cloacae G04去除Cr(VI)的较优反应条件为初始pH5. 0、温度37℃、Cr(VI)浓度为100 mg·L~(-1)、装液量80 mL(250 mL三角瓶)、接种量15%、摇床转速为120r·min~(-1)、反应时间48 h。在此条件下,菌株E. cloacae G04对Cr(VI)和总铬的去除率分别为84%和8%。根据Cr(VI)去除率和总铬去除率的结果推测该菌株去除Cr(VI)的机制可能是以还原为主、吸附为辅。这表明李氏禾内生细菌E. cloacae G04菌株具有较好的应用潜力,既有可能直接用于土壤、水环境铬污染的修复,也有可能作为促植物修复铬污染的后备菌株,另外可为深入研究李氏禾的铬积累作用机制提供参考。     

As(V) Reduction,As(III) Oxidation,and Cr(VI) Reduction by Multi-metal-resistant Bacillus subtilis,Bacillus safensis,and Bacillus cereus Species Isolated from Wastewater Treatment Plant

Industrial progress has resulted in threatening concentrations of toxic metals in various areas of the world. Bioremediation is an economical alternative to chemical methods. Bacteria resistant to As(III), As(V), Cr, Co, Cu, Cd, Hg, Ni, Pb, Se, and Zn were isolated from the wastewater treatment plant of Kasur, Pakistan. Highest resistance against all metals was exhibited by MX-1, MX-3, MX-4, and MX-5. The isolates possessed dual ability to oxidize as well as to reduce As. Highest As(V) reduction (454 µM) was exhibited by MX-1, while most As(III) oxidation was shown by MX-3 (170 µM). The isolates were also capable of reducing Cr(VI), and maximum Cr(VI) reduction (500 µM) was exhibited by MX-3. Transformation of DH5α with MX-1 plasmid showed that resistance genes for As(III), As(V), Cr, Cd, Se, Hg, and Ni were plasmid borne, while in case of MX-3, resistance genes for As(III), As(V), Co, Cu, Se, Pb, Zn, and Ni were present on plasmid. MX-1 and MX-3 were also positive for auxin production (37 and 32.96 µg ml^?1, respectively). MX-3 was also found to produce hydrogen cyanide (HCN) and solubilized phosphate. These isolates promoted plant (Vigna radiata) growth both in the presence and absence of the metals. MX-1, MX-3, and MX-5 were identified as Bacillus subtilis, Bacillus safensis, and Bacillus cereus through 16S rRNA gene sequencing, respectively. Such bacteria having multiple traits of resisting multiple metals, dual ability to oxidize/reduce As, and reduce Cr(VI) along with the ability to support plant growth are good tools for remediation of metal-contaminated sites and its cultivation.     

Isotherm Modelling,Kinetic Study and Optimization of Batch Parameters Using Response Surface Methodology for Effective Removal of Cr(VI) Using Fungal Biomass

Biosorption is a promising alternative method to replace the existing conventional technique for Cr(VI) removal from the industrial effluent. In the present experimental design, the removal of Cr(VI) from the aqueous solution was studied by Aspergillus niger MSR4 under different environmental conditions in the batch systems. The optimum conditions of biosorption were determined by investigating pH (2.0) and temperature (27°C). The effects of parameters such as biomass dosage (g/L), initial Cr(VI) concentration (mg/L) and contact time (min) on Cr(VI) biosorption were analyzed using a three parameter Box–Behnken design (BBD). The experimental data well fitted to the Langmuir isotherm, in comparison to the other isotherm models tested. The results of the D-R isotherm model suggested that a chemical ion-exchange mechanism was involved in the biosorption process. The biosorption process followed the pseudo-second-order kinetic model, which indicates that the rate limiting step is chemisorption process. Fourier transform infrared (FT-IR) spectroscopic studies revealed the possible involvement of functional groups, such as hydroxyl, carboxyl, amino and carbonyl group in the biosorption process. The thermodynamic parameters for Cr(VI) biosorption were also calculated, and the negative ∆Gº values indicated the spontaneous nature of biosorption process.     

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).     

Adaptation of growth and photosynthesis to certain temperature regimes is an indicator for the geographical distribution of Cosmarium strains (Zygnematophyceae,Streptophyta)

In contrast to the many investigations on possible relationships between climate and geographical distributions in macroalgae, there are almost no similar studies regarding microalgae. In this study we consider the potential influence of temperature on patterns of distribution of six Cosmarium strains isolated from various climate zones that have been cultured long-term (> 15 years) in a relatively low temperature–low light regime. Growth and photosynthetic parameters, obtained from PAM fluorometry, were used to estimate the physiological characteristics of the strains during and after various temperature treatments. Acclimation to constant temperature and light conditions tended to affect photosynthetic parameters more than algal growth characteristics. However, all of the Cosmarium strains demonstrated physiological responses that were consistent with their source location under both low and high temperature conditions, confirming that such responses are genetically preserved. The Cosmarium strains displayed photosynthetic capacities and levels of the onset of saturation that repeatedly exceeded values recorded for other microalgae and seaweeds, indicating that these desmid strains are adapted to high light. This observation, as well as the relatively high growth temperature optima for all of the Cosmarium strains, provides some support for Coesel's hypothesis on the origin of desmids in the tropical zone. Interestingly, the Cosmarium strains used in this study demonstrated not only adaptive characteristics in accordance with the temperature prevailing at their sampling sites, but also with regard to their evolutionary origin.