Biosorption properties of dried Neurospora crassa for the removal of Burazol Blue ED dye

Biosorption potential of dried Neurospora crassa for Burazol Blue ED was studied with respect to pH, equilibrium time, biomass concentration and temperature to determine equilibrium and kinetic model parameters. The most suitable pH, equilibrium time and biomass concentration were determined as 1 ± 0.2, 60 min and 1.6 g L^− 1, respectively, at 20 °C ± 1.0. The equilibrium data was best described by the Langmuir isotherm model. The maximum biosorption capacity (q_m) of biomass obtained from the Langmuir fit was 110.1 mg g^− 1 biomass at 30 °C. The overall biosorption process was best described by the pseudo-second-order kinetic model. The biosorption process was found to be favored at higher temperatures.     

Electrocatalytic reduction of chromium by poly(aniline-co-o-aminophenol): An efficient and recyclable way to remove Cr(VI) in wastewater

Poly(aniline-co-o-aminophenol) (PANOA)-modified glassy carbon electrode (GCE) was first used to investigate the electrocatalytic reduction of dichromate in a NaCl solution of pH 5.0. The results of cyclic voltammograms and UV–vis spectra demonstrated that the reduction of Cr(VI) occurred at PANOA-modified GCE. The FT-IR, ESR and XPS results showed that the Cr(VI) can be doped in the PANOA films and can convert to less-toxic Cr(III). The doping level Cr/N was 78.2% and trace amount of Cl (0.42%) was detected in the doped PANOA, which indicated that the doping process is effective and PANOA had rather good ion selectivity in the 0.10 M NaCl supporting electrolyte. The factors influenced the reduction were also considered. Various initial concentrations of Cr(VI) had different removal rates. The maximum removal rate of Cr(VI) at 20 mg L⁻¹ (32.3%) was better than that of at 5 mg L⁻¹ (22.9%). The solution pH had little effect on Cr(VI) reduction and doping process of the PANOA because PANOA had good electrochemical activity and stability in a wide range of pHs (from pH 4 to pH 8).     

生物质吸附材料对Cr(VI)的吸附还原研究进展

重金属污染是当今工业发展所面临的一个重要环境问题,传统处理含铬废水的方法具有工艺简单、操作方便等优点,但存在二次污染、处理成本高等问题。寻找成本低、去除效率高的重金属废水处理方法是当下研究的一个重要方向。本工作介绍了生物质吸附法对含铬废水的处理研究,简述了生物质材料在金属吸附回收领域的优势,分析了当前生物质吸附材料的研究内容和发展现状,归纳了目前常用的物理、化学改性方法,并详细介绍了改性生物质材料对Cr(VI)的吸附效果,然后根据吸附剂表面活性基团与吸附质之间相互作用的类型,分析总结了生物质吸附材料对Cr(VI)的四种吸附机理以及在吸附过程中氨基、羟基、硫醇等活性基团作为电子供体对Cr(VI)的还原机理。最后,从研究与应用的角度,对生物质吸附材料吸附还原Cr(VI)的未来研究方向做出展望。     

Improvement of the growth of Arthrospira (Spirulina) platensis from Toliara (Madagascar): Effect of agitation, salinity and CO2 addition

Arthrospira (Spirulina) platensis Toliara isolated from alkaline and salt lakes in the south-western area of Madagascar is a potential source of proteins that could efficiently fight against food deficiency in developing countries like Madagascar. Up to now, productivity in this country has been low, so a better understanding of the growth conditions of this species is needed to improve its production. Growth experiments were undertaken in bubble columns at laboratory scale. The influence of agitation of the culture, medium salinity (ranging from 13 to 35 g L⁻¹) and CO₂ addition (ranging from 0 to 2%, v/v) on growth and protein content was examined. Because Arthrospira cells are fragile, a bubble column without additional mixing gave the best growth. Arthrospira (Spirulina) platensis showed higher specific growth rate (μ_max) and protein content for lower salinity. Addition of 1% of CO₂ improved the productivity by near 60%. The feasability of semi-continuous culture was demonstrated and optimal culture conditions led to a mean productivity of 0.22 ± 0.03 g L⁻¹ d⁻¹, a mean specific growth rate of 0.015 ± 0.002 h⁻¹ and a protein content of 53 ± 2% of total dry weight.     

The biosorption of Cr(VI) ions by dried biomass obtained from a chromium-resistant bacterium

The biosorption potential of many different kinds of biomaterials has been widely studied. However, there is little data on the biosorption mechanism of Cr(VI) by dried biomass. So the bio-removal of Cr(VI) ions from aqueous solutions was investigated using dried biomass from a chromium-resistant bacterium. The bacterium was isolated from dewatered sludge samples that were obtained from a sewage treatment plant. Equilibrium and kinetic experiments were performed at different metal concentrations, pH values, and biosorbents dosages. The biomass was characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The functional groups in the Bacillus cereus biomass which may play a role in the biosorption process were identified by Fourier transform infrared spectroscopy. The biosorption process was found to be highly pH dependent and the optimum pH for the adsorption of Cr(VI) was 2.0±0.3 at 30±2 °C. The experimental data fit well with Langmuir and Freundlich models as well as a pseudo-second order kinetic model. The mechanism for the biosorption was also studied by fitting the kinetic data with an intra-particle diffusion model and a Boyd plot. External mass transfer was found to be the rate-determining step for the adsorption process. Biosorption could be an alternative mechanism besides bio-oxidation and bio-reduction for the bioremediation of heavy metals.     

Organic arsenic removal from an aqueous solution by iron oxide-coated fungal biomass: An analysis of factors influencing adsorption

A two-level seven-factor (2^7-2) fractional factorial design analysis was conducted to examine the parameters influencing dimethylarsinic acid (DMA) removal from an aqueous solution using iron oxide-coated A. niger biomass. The factors examined were the concentration of DMA in solution, the mass of the adsorbent, the solution temperature, the Ca²⁺ ions in solution, the Fe²⁺ ions in solution, the SO₄²⁻ ions in solution, and the Cl⁻ ions in solution. The magnitude of the influence of the factors considered on DMA removal was observed in the order: presence of Ca²⁺ ions in solution > the DMA concentration > solution temperature > presence of SO₄²⁻ in solution > presence of Fe²⁺ in solution > the mass of adsorbent > the presence of Cl⁻ in solution.     

Activation of Phillips Cr/silica catalysts: IV. Mobility of Cr(VI)

The saturation coverage behavior of Cr(VI) on silica has been used to study the mobility of hexavalent chromium during commercial activation of the Phillips catalyst in a fluidized bed. Cr(VI) was found to migrate not only within each silica particle, but even between particles. The mechanism of transfer is thought to be particle-to-particle contact during the fluid bed calcining process, and Cr migration was observed at temperatures as low as 300–400 °C in these experiments. Transfer can take place even in the absence of oxygen, which suggests that redox cycling is probably not the main method of mobility. However, once the silica is calcined at high temperatures the migration is stopped at low temperatures, indicating that the thermal history of the surface is important in the transfer process. Migration of Cr on and between alumina particles behaved in much the same way, and Cr transfer was also observed between silica and alumina in both directions. Cr(III) on deactivated commercial Cr/silica catalysts could be reclaimed to Cr(VI) surprisingly easily by co-activation with virgin support. The spreading out of Cr(VI) onto a fresh unoccupied surface probably provides a powerful force to reoxidize the otherwise seemingly inert alpha-Cr₂O₃ crystallites. The mobility has important consequences for commercial manufacture and use of the catalyst.     

Effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution by modified polyethyleneimine

A novel flocculant with the capacities of reduction and chelation was prepared in this paper. The flocculant, called polyethyleneimine–sodium xanthogenate (PEX), was synthesized by modifying polyethyleneimine with carbon disulfide and sodium hydroxide. The effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution with PEX was investigated by using flocculation experiments. The results showed that in the single-ion system (only including Cr(III) or Cr(VI) in the solution), the final Cr(III) decreased with the increase in pH from 2.0 to 10.0, while the final Cr(VI) increased at first and then decreased with the increase in this pH range studied. The removal of Cr(III) was not desirable at pH lower than 7.0, whereas the final Cr(VI) concentration reached the minimum value of 0.145 mg/L at pH 2.0. In the mixture system of Cr(III) and Cr(VI), the variation tendency for the removal of Cr(III) or Cr(VI) was very similar to that obtained in the single-ion system. The oxidation–reduction potential, zeta potential, and final pH in the supernatant were also measured to analyze the above results. Furthermore, FTIR spectra revealed that dithiocarboxylic acid groups on the macromolecular chains of PEX played a major role in the Cr(VI) reduction and Cr(III) chelation.     

Synthesis of Ethyl 5 Z ,9 Z ,12 Z -octadecatrienoate (ethyl pinolenate) and Methyl 12 Z ,15 Z -octadecadienoate

Pinolenic acid (5Z,9Z,12Z-octadecatrienoic acid, 1a), one of the most abundant trienoic fatty acids in nature, is very difficult to obtain in quantity in a pure state from the highly complex mixture of unsaturated tall oil fatty acids. For this reason its chemistry has been little studied when compared to linolenic or linoleic acids. A simple synthesis of esters of 1a and of 12Z,15Z-octadecadienoic acid 3 using the one pot double Wittig procedure is described here. The products of double Wittig reactions were purified by argentation chromatography, and their structural purity was established by ¹H-, ¹³C-NMR and 2D-NMR spectroscopies.

Simultaneous recovery of Cr(III) and Cr(VI) from the aqueous phase with ion-exchange membranes

The simultaneous recovery of trivalent and tetravalent chromium ions through charged ion-exchange membranes by using three detachable cells was tested at different current densities. The effect of mono- and divalent valence ions corresponding to trivalent and hexavalent chromium ions in the feed phase was investigated. The recovery factor values of chromium (III) and (VI) ion without current density were obtained and found that it was higher in the absence of binary monovalent and divalent ions, but increased with increasing current density and decreased in the presence of the binary mono- and divalent ions. The transport of both oxidation states of chromium ions through membranes was also correlated with the flux data.     

Sorption of boron by invasive marine seaweed: Caulerpa racemosa var. cylindracea

The sorption of boron from aqueous solution onto Caulerpa racemosa var. cylindracea (CRC), collected from Seferihisar/Izmir region in Turkey, was investigated as a function of pH, temperature, initial boron concentration, adsorbent dosage, contact time and ionic strength. Optimum conditions for the sorption of boron were obtained at pH 7.5, 318 K, 8 mg L⁻¹ initial boron concentration, 0.2 g of CRC, 2.5 h contact time and greater ionic strength (10⁻¹ M NaCl). As the temperature was increased the boron removal took place with higher percentages. In experiments conducted at optimum conditions, maximum boron sorption was determined to be about 63%. The experimental data were analyzed by Freundlich, Langmuir and Dubinin–Radusckevich (DR) equations. Freundlich and DR models provide best conformity with the experimental data. In order to describe kinetics of boron sorption onto CRC, first-order Lagergren equation, pseudo-second-order kinetic model and intraparticle diffusion model were used. It was seen that the first order Lagergren equation was better described than the pseudo-second-order kinetic model. Thermodynamic parameters of sorption process were also calculated. It was obtained that sorption process was not spontaneous. The characterization of CRC was carried out by Fourier transform infrared spectroscopy (FTIR) analysis.     

Required equilibrium studies for designing a three-phase bioreactor to degrade trichloroethylene (TCE) and tetrachloroethylene (PCE) by Trametes versicolor

This paper aims to investigate the three-phase equilibriums to design a bioreactor to degrade trichloroethylene (TCE) and tetrachloroethylene (PCE) by the white-rot fungus Trametes versicolor. The vapour–liquid equilibrium constants were obtained from bibliographic values and these values are 0.392 for TCE and 0.723 for PCE, which show that these two compounds are very volatile. Adsorption of TCE and PCE by dead biomass pellets was studied. Due to the low concentration range studied for both compounds, the linear equation is enough to describe the adsorption equilibrium. The adsorption parameters are 0.110 and 0.176 for TCE and PCE, respectively. Then the equilibrium information obtained was used to calculate the distribution of these contaminants in a three-phase bioreactor in specific degradation conditions and despite it is checked that adsorption is not very high, it is significant (between 12.0% and 12.8%). Moreover, a comparison between TCE and PCE experimental and calculated degradation yields was done to validate the linear isotherm.     

Removal of Cr(VI) from water using Fe(II)-modified natural zeolite

In this study, natural zeolite aggregates with the particle size of 1.4–2.4 mm were modified by Fe(II). The unmodified zeolite and Fe(II)-modified zeolite (Fe-eZ) were subjected to batch and column tests to study the Cr(VI) sorption, transport, and retardation. Modification of the natural zeolite with Fe(II) resulted in an increase in Cr(VI) sorption to 6 mmol/kg. The Cr(VI) sorption followed a pseudo-second-order kinetics with a rate of 17 mmol/g h and a rate constant of 0.7 g/mmol h. Cr(VI) removal from solution increased with an increase in ionic strength, but decreased as the solution pH increased. At a Cr(VI) input concentration of 100 mg/L, unmodified zeolite did not show any Cr(VI) retardation at all. In contrast, the observed retardation factor of Fe-eZ for Cr(VI) increased by a factor of 6. The hydraulic conductivity of the zeolite showed little change before and after Fe(II) modification and before and after Cr(VI) sorption, suggesting its good mechanical stability to be used as packing materials for permeable reactive barriers in groundwater remediation.     

Uptake of Cr (VI) by Sphingomonas paucimobilis Biomass from Aqueous Solutions

The Sphingomonas paucimobilis biomass has been successfully utilized to degrade several persistent organic pollutants (POPs). However, few studies have been conducted to use it to remove heavy metals from aqueous solutions. In the present study, biosorption experiments for Cr (VI) were investigated using nonliving biomass of S. paucimobilis isolated from activated sludge, Lianyungang Dapu sewage treatment plant, China. The effects of several parameters including solution pH, contact time, and ionic strength, etc. on Cr (VI) uptake were studied. The biomass was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectrometer (FTIR). The applicability of the Langmuir and Freundlich models was tested. The correlation coefficients (R) of both models were greater than 0.95. The maximum adsorption capacities were found to be 28.5 mg/g for Cr (VI) at 20°C. The adsorption process was quick and found to follow the pseudo-second-order equation. The optimum adsorption was achieved at pH 2. The adsorption was also NaCl concentrations dependent.     

An experimental and computational study of intramolecular charge transfer: Diarylamino derivatives of 7H-benzimidazo(2,1-a)benz(d,e)isoquinolin-7-ones

A novel intramolecular donor–acceptor system of four isomers consisting of 7H-benzimidazo(2,1-a)benz(d,e)isoquinolin-7-ones and diarylamine units was synthesized and characterized; the absorption and fluorescence spectra of the system in a variety of solvents were investigated. Intramolecular charge transfer was confirmed within the system by virtue of shifts in emission maximum with increasing solvent polarity; a high dipole moment for the intramolecular excited state was calculated using the Lippert equation. Shorter lifetimes were observed in polar solvents compared with those in non-polar solvents, indicating strong dipole–dipole interactions occurred. The ground-state geometry, lowest energy transition and the UV–vis spectrum of the system were studied using density functional theory and time-dependent density functional theory at B3LYP/6-31G^* level, which showed that the calculated outcomes were in good agreement with experimental data.     

Reduction of Cr(VI) by palladized biomass of Desulfovibrio vulgaris NCIMB 8303

Palladized biomass of Desulfovibrio vulgaris (Bio‐Pd(0)) reduced Cr(VI) to Cr(III) at an initial rate four‐fold higher than chemically‐prepared Pd(0) metal. Optimal Cr(VI) reduction by suspended Bio‐Pd(0) occurred at pH 3, whereas pH did not affect the rate of Cr(VI) reduction by Bio‐Pd(0) immobilized in agar beads. The rate of Cr(VI) reduction was concentration‐dependent below 300 µmol dm^?3, and application of enzyme kinetics, considering Bio‐Pd(0) as an ‘artificial enzyme’, gave an apparent K_m (K_mapp) of approx. 650 µmol dm^?3 and V_max of 1667 nmol h^?1 mg Pd(0) for suspended Bio‐Pd(0). The potential of Bio‐Pd(0) as a method for the treatment of Cr(VI)‐wastes is discussed. Copyright © 2005 Society of Chemical Industry     

Nanorod-pillared mesoporous rGO/ZnO/Au hybrids for photocatalytic Cr (VI) reduction: Enhanced Cr(VI) adsorption and solar energy harvest

Herein, we fabricated mesoporous ternary hybrids composed of Au-functionalized ZnO nanorods grown on rGO nanosheets. The ZnO nanorods distributed on the rGO nanosheets can act as a pillaring layer to avoid the agglomeration of rGO, leading to the formation of abundant mesopores within the hybrids. The high-surface-area, mesoporous hybrids can offer sufficient active sites and transport channels for efficient adsorption and diffusion of Cr(VI), which was favorable for its photocatalytic reduction due to the adsorption enrichment effects. Moreover, the plasmonic-induced visible-light absorption of Au nanoparticles and efficient charge separation by rGO synergistically contributed to the significantly improved solar-light-driven photocatalytic Cr(VI) reduction properties of the ternary hybrids.     

Highly efficient photocatalytic reduction of Cr(VI) by bismuth hollow nanospheres

Uniform bismuth hollow nanospheres with efficient Cr(VI) adsorption capacities were used to the photodegradation of highly toxic Cr(VI) for the first time, which exhibited outstanding visible-light photocatalytic abilities for the reduction of Cr(VI) to less toxic Cr(III).     

Numerical study of co-firing coal and Cynara cardunculus in a 350 MWe utility boiler

In this work, a CFD numerical study of co-firing coal and cynara in a 350 MWe utility boiler is presented. The most influent operational factors related to the biomass feeding conditions such as biomass mean particle size, level of substitution of coal by biomass and feeding location in the furnace, are analyzed, determining their influence in the combustion process. Validation of the simulations is performed using measurements gathered at the plant. Results from the study show interesting conclusions for their implementation in the power plant, suggesting recommendable limits in the maximum biomass substitution level and particle size in order to keep a reasonable boiler efficiency, and pointing out the outstanding influence of the biomass injection location discussing thermal and fluid-dynamic implications and the possibility of introducing retrofitted or specific biomass burners.     

Adsorption of Cr(VI) and As(III) on coaly activated carbon in single and binary systems

In single component system, the adsorption of Cr(VI) and As(III) increase with contact time. Solution pH is found influencing the adsorption. Cr(VI) removal is found to be maximum (98%) at pH = 2. While, As(III) removal is found to be maximum at pH = 6 (77.2%). The adsorption capacity of Cr(VI) is greater than that of As(III) in single component system. Several adsorption isotherms were used to fit the equilibrium data. The adsorption kinetic data of Cr(VI) and As(III) were analyzed and is found fitting well in a pseudo-second-order equation both in single and binary systems. In binary system, the adsorption of As(III) is generally higher than that in single system. The pseudo-second-order rate constant k₂ is 0.5037 g/mg min in binary system larger than 0.0782 g/mg min in single system. However, the presence of As(III) in solution does not significantly influence the capacity of Cr(VI) adsorption on coaly activated carbon (CAC). The complexation between Cr(VI) and As(III) influence the adsorption, resulting in increased adsorption of As(III). The complexation structure of As(III), Cr(VI) and CAC was proposed as A-Cr(VI)-As(III) (A represents the adsorption site on the CAC).