Application of equilibrium and mass transfer models to dynamic removal of Cr(VI) ions by Chitin in packed column reactor

The dynamic removal of hexavalent chromium by chitin flakes was studied in a packed column reactor. The values of column parameters were predicted as a function of flow rate, bed depth, particle size and inlet metal ion concentration. On evaluating the breakthrough curves, sorption isotherms were obtained and modelled according to the Langmuir, the Redlich–Peterson and the Freundlich models. Kinetic and mass transfer aspects of the dynamic removal of Cr(VI) ions by chitin were investigated using several mathematical models. Column studies showed a good correlation between the experimental data and the calculated breakthrough curves obtained by the Adams–Bohart or the Wolborska models and the Clark model. The simulation of the whole breakthrough curve was effective with the Clark model, but the breakthrough was best predicted by Adams–Bohart, or related derived models.     

Biosorption of Cu2+, Cd2+, Pb2+, and Zn2+ using dried marine green macroalga Caulerpa lentillifera

The sorption of Cu2+, Cd2+, Pb2+, and Zn2+ by a dried green macroalga Caulerpa lentillifera was investigated. The removal efficiency increased with pH. The analysis with FT-IR indicated that possible functional groups involved in metal sorption by this alga were O-H bending, N-H bending, N-H stretching, C-N stretching, C-O, SO stretching, and S-O stretching. The sorption of all metal ions rapidly reached equilibrium within 20min. The sorption kinetics of these metals were governed by external mass transfer and intraparticle diffusion processes. The sorption isotherm followed the Langmuir isotherm where the maximum sorption capacities was Pb2+>Cu2+>Cd2+>Zn2+.     

Batch and column studies of biosorption of heavy metals by Caulerpa lentillifera

The biosorption of Cu(II), Cd(II), and Pb(II) by a dried green macroalga Caulerpa lentillifera was investigated. The sorption kinetic data could be fitted to the pseudo second order kinetic model. The governing transport mechanisms in the sorption process were both external mass transfer and intra-particle diffusion. Isotherm data followed the Sips isotherm model with the exponent of approximately unity suggesting that these biosorption could be described reasonably well with the Langmuir isotherm. The maximum sorption capacities of the various metal components on C. lentillifera biomass could be prioritized in order from high to low as: Pb(II)>Cu(II)>Cd(II). The sorption energies obtained from the Dubinin-Radushkevich model for all sorption systems were in the range of 4-6 kJ mol(-1) indicating that a physical electrostatic force was potentially involved in the sorption process. Thomas model could well describe the breakthrough data from column experiments. Ca(II), Mg(II), and Mn(II) were the major ions released from the algal biomass during the sorption which revealed that ion exchange was one of the main sorption mechanisms.     

Equilibrium of Cu(II) and Ni(II) biosorption by marine alga Sargassum filipendula in a dynamic system: competitiveness and selectivity

The study focuses on the equilibrium of dynamic biosorption in single and binary systems containing Cu(II) and Ni(II) ions using Sargassum filipendula (a marine alga). The experiments were performed in fixed-bed columns with both single-component and bi-component metal solutions (using different molar concentrations). Experimental data were fitted with different equilibrium models such as Langmuir, Langmuir with inhibition, Jain and Snowyink and Langmuir-Freundlich equations. The biosorption of pure metal ions in solution presented adequate capacities both for Cu(II) and Ni(II). In binary solutions the preferential sorption of Cu(II) over Ni(II) was demonstrated by the displacement of Ni(II) (marked overshoot on the breakthrough curves).     

The influence of particle size distribution and operating conditions on the adsorption performance in fluidized beds

The influence of matrix properties and operating conditions on the performance in fluidized-bed adsorption has been studied using Streamline diethyl-aminoethyl (DEAE), an ion exchange matrix based on quartz-weighted agarose, and bovine serum albumin (BSA) as a model protein. Three different particle size fractions (120-160 mum, 120-300 mum, and 250-300 mum) were investigated. Dispersion in the liquid phase was reduced when particles with a wide size distribution were fluidized compared to narrow particle size distributions. When the mean particle diameter was reduced, the breakthrough capacities during frontal adsorption were enlarged due to a shorter diffusion path length within the matrix. At small particle diameters the effect of film mass transfer became more relevant to the adsorption performance in comparison to larger particles. Therefore matrices designed for fluidized-bed adsorption should have small particle diameter and increased mean particle density to ensure small diffusion path length in the particle and a high interstitial velocity to improve film mass transfer. Studies on the influence of sedimented matrix height on axial mixing showed an increased Bodenstein number with increasing bed length. Higher breakthrough capacities were also found for longer adsorbent beds due to reduced dispersion and improved fluid and particle side mass transfer. With increasing bed height the influence of flow rate on breakthrough capacity was reduced. For a settled bed height of 50 cm breakthrough capacities of 80% of the equilibrium capacity for flow rates varying from 3 to 9 cm/min could be achieved. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 54-64, 1997.     

Continuous Biosorption of Pb,Cu, and Cd by Phanerochaete chrysosporium in a Packed Column Reactor

The dynamic removal of lead, copper and cadmium in a single component system by Phanerochaete chrysosporium was studied in packed columns. The packed columns consisted of biomass of P. chrysosporium immobilized on polyurethane foam cubes. The performances of packed columns were described through the concept of breakthrough and the values of column parameters predicted as a function of bed depth. The column biosorption data were evaluated in terms of maximum (equilibrium) capacity of the column, the amount of metal loading and the yield of the process. The maximum capacities for lead, copper and cadmium were 70.7, 43.7 and 70.8 mg, respectively, and their yields were 39.2, 40.6 and 41%, respectively. The kinetic and mass transfer aspects of the dynamic removal of the three metals were studied using three mathematical models commonly used to describe the column performance in adsorption processes. Column studies showed good agreement between the experimental data and the simulated breakthrough curves obtained with Adams-Bohart or the Wolborska model and the Clark model. While the initial segment of the breakthrough curve was defined by the Adams-Bohart and Wolborska models, the whole breakthrough curve was well predicted by the Clark model for all the three metals studied.     

Experimental and modeling studies on the sorption breakthrough behaviors of butanol from aqueous solution in a fixed-bed of KA-I resin

Removal of biobutanol from acetone-butanolethanol (ABE) fermentation broth can be achieved by fixed-bed sorption by means of KA-I resin, and the relevant breakthrough curves would provide much valuable information to help design a continuous fixed-bed sorption process in field application. In the present study, the effects of several important design parameters, i.e., initial butanol concentration (C _f: 3.0 ～ 30.0 g/L), inlet flow rate (Q _f: 0.5 ～ 5.5 mL/min) and adsorbent bed height (Z: 4.2 ～ 18.0 cm), on the adsorption breakthrough curves of KA-I resin in a fixed-bed column were investigated. It was found that the amount of adsorbed butanol at breakthrough point was increased with an increase in the value of C _f and Z; and with decrease in the value of Q _f. However, the maximum sorption capacities of butanol at saturated point were basically unchanged. Three well-established fixed-bed adsorption models, namely Thomas, Yoon-Nelson and Adams-Bohart, were applied to predict the breakthrough curves and to determine the characteristic parameters of fixed-bed column, which are the basis for the process design at a real scale. Good agreement between the theoretical breakthrough curves and the experimental result were observed using Thomas and Yoon-Nelson models.     

Preparation and Characterization of Chemically Modified Silk Cotton Hull Activated Carbon and Its Effects on Cd(II) Removal from Aqueous Solutions

The novel biosorbent silk cotton hull, an agrowaste material, has been successfully utilized for the removal of cadmium(II) from aqueous solutions. The adsorption of cadmium onto three kinds of activated biosorbent has been studied: modified by concentrated sulfuric acid alone (AC), a mixture of concentrated sulfuric acid and hydrogen peroxide (AC1), and a mixture of concentrated sulfuric acid and ammonium persulfate (AC2). The adsorption studies were carried out to optimize the process parameters such as pH, adsorbent dosage, contact time, and initial metal ion concentration. Maximum metal removal was observed at pH 7.0 with a contact time of 90 min at stirring speed of 200 rpm with an adsorbent dosage of 4.0 g L^?1. The sorption isotherms were studied using the Langmuir, Freundlich, and Tempkin isotherm models. The maximum adsorption capacities were 100.00, 142.86, and 142.87 mg g^?1 for AC, AC1, and AC2, respectively. Accordingly, the surface modification of the activated carbons AC1 and AC2 enhanced cadmium removal greatly. The experiments demonstrated that the removal of metal ions followed the pseudo-second-order kinetic model. The sorption mechanism is discussed in terms of the activated surface properties. A relationship between the oxygen content and sorption was found in this novel material. Desorption experiments were carried out using hydrochloric acid with a view to generate the spent adsorbent and to recover the adsorbed metal ions.     

Heavy metal biosorption by fungal mycelial by-products: mechanisms and influence of pH

Summary Mycelial wastes of Rhizopus arrhizus, used in fermentation industries to produce lipases, were studied for their ability to absorb various heavy metal ions (Ni, Zn, Cd and Pb). Chelation of all these ions occurs by a chemical, equilibrated and saturatable mechanism, following the Langmuir adsorption model. Data transformation allowed us to calculate maximum uptake and dissociation constants of the sorption reaction. We also investigated the influence of pH on metal accumulation. Sorption capacity variations between different biosorbent types (Rhizopus, Mucor, Penicillium, and Aspergillus), could be related to their acidity. pH neutralisation during the sorption reaction considerably enhanced zinc chelation (up to 56 mg/g). Previous NaOH treatment of mycelial wastes also increased their capacity for metal sorption. We report R. arrhizus metal uptake curves versus pH, using a pH-stat system. Optimal adsorption was achieved at neutral pH for nickel and zinc, pH 5.0 for lead, and inhibition of chelation was observed when the pH decreased. These results illustrate the importance of pH during the adsorption process, indicating a competitive mechanism for chelation between heavy metal ions and protons at cell wall adsorption sites. Correspondence to: J.-C. Roux     

Synergistic Removal of Pb(II), Cd(II) and Humic Acid by Fe3O4@Mesoporous Silica-Graphene Oxide Composites

The synergistic adsorption of heavy metal ions and humic acid can be very challenging. This is largely because of their competitive adsorption onto most adsorbent materials. Hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO) were here prepared to address this. Magnetic mesoporous silica microspheres were synthesized and functionalized with PEI molecules, providing many amine groups for chemical conjugation with the carboxyl groups on GO sheets and enhanced the affinity between the pollutants and the mesoporous silica. The features of the composites were characterized using TEM, SEM, TGA, DLS, and VSM measurements. Series adsorption results proved that this system was suitable for simultaneous and efficient removal of heavy metal ions and humic acid using MMSP-GO composites as adsorbents. The maximum adsorption capacities of MMSP-GO for Pb(II) and Cd (II) were 333 and 167 mg g⁻¹ caculated by Langmuir model, respectively. HA enhances adsorption of heavy metals by MMSP-GO composites due to their interactions in aqueous solutions. The underlying mechanism of synergistic adsorption of heavy metal ions and humic acid were discussed. MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.     

Metal-binding capacity of arbuscular mycorrhizal mycelium

Experiments with excised mycelium of several Glomus spp. with different histories of exposure to heavy metals were carried out to measure their capacities to bind Cd and Zn. Cd sorption was followed for up to 6 h of incubation to determine its time course relationships. Controls treated with a metabolic inhibitor were included to evaluate whether sorption was due to active uptake or passive adsorption. The effect of ion competition (effects of Ca or Zn on Cd sorption) and general measurements of cation exchange capacity (CEC) of roots and hyphae were also performed. The results showed that AM mycelium has a high metal sorption capacity relative to other microorganisms, and a CEC comparable to other fungi. Metal sorption was rapid (<30 min) and appeared mainly to be due to passive adsorption. Adsorption was highest in a metal-tolerant G. mosseae isolate and intermediate for a fungus isolated from a soil treated with metal-contaminated sludge. The former adsorbed up to 0.5 mg Cd per mg dry biomass, which was three times the binding capacity of non-tolerant fungi, and more than 10 times higher than reported values for, e.g., the commonly used biosorption organism Rhizopus arrhizus. The implications of these results for AM involvement in plant protection against excess heavy metal uptake are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimization of affinity and ion-exchange chromatographic processes for the purification of proteins

This study documents several alternative approaches for the optimization of the ion-exchange and affinity chromatographic purification of proteins. In these approaches, the chromatographic process has been treated as a four-stage (adsorption, washing, elution, and regeneration) operation. Central to these investigations has been the elaboration of practical iterative procedures based on the use of theoretical models describing each of these stages. Predictions derived from these models have then been evaluated in terms of experimental data obtained using batch adsorption measurements in finite bath configurations and frontal breakthrough measurements with packed beds of different dimensions, containing nonporous and porous adsorbents of different selectivities and capacities for proteins. Commencing with the kinetic and distribution parameters derived from batch equilibrium measurements, the effect of the initial concentration of the target protein, the solid-liquid volume ratio, the superficial velocity and the column dimensions on the pressure drop, production rate, concentration profile, column utilization, and yield have been determined with packed beds. The potential of these iterative approaches to simplify the determination of key mass transfer and interaction parameters required for scale-up and economic optimization of chromatographic purifications of proteins has been examined using ion exchange, immobilized metal ion affinity, and triazine dye pseudo-affinity adsorbents of different selectivity and adsorption capacities. (c) 1996 John Wiley & Sons, Inc.     

Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r² = 0.932-0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the kinetics of metal biosorption due either to prefixed order or unjustifiable change in rate constant and reaction order with varying concentrations of metal and biomass in the solution. The diffusion-based models, namely, the intra-particle diffusion model and the external mass transfer model fitted well to the time-course metal sorption data, thus suggesting involvement of both external and intra-particle diffusion processes in sorption of test metals by mat biomass. However, the Boyd kinetic expression clearly showed that the external mass transfer is the dominant process.     

Biosorption of lead(II), cadmium(II), copper(II) and nickel(II) by anaerobic granular biomass

Biosorption is potentially an attractive technology for treatment of wastewater for retaining heavy metals from dilute solutions. This study investigated the feasibility of anaerobic granules as a novel type of biosorbent, for lead, copper, cadmium, and nickel removal from aqueous solutions. Anaerobic sludge supplied from a wastewater treatment plant in the province of Quebec was used. Anaerobic granules are microbial aggregates with a strong, compact and porous structure and excellent settling ability. After treatment of the biomass with Ca ions, the cation exchange capacity of the biomass was approximately 111 meq/100 g of biomass dry weight which is comparable to the metal binding capacities of commercial ion exchange resins. This work investigated the equilibrium, batch dynamics for the biosorption process. Binding capacity experiments using viable biomass revealed a higher value than those for nonviable biomass. Binding capacity experiments using non-viable biomass treated with Ca revealed a high value of metals uptake. The solution initial pH value affected metal sorption. Over the pH range of 4.0-5.5, pH-related effects were not significant. Meanwhile, at lower pH values the uptake capacity decreased. Time dependency experiments for the metal ions uptake showed that adsorption equilibrium was reached almost 30 min after metal addition. It was found that the q(max) for Pb2+, Cd2+, Cu2+, and Ni2+ ions, were 255, 60, 55, and 26 mg/g respectively (1.23, 0.53, 0.87, and 0.44 mmol/g respectively). The data pertaining to the sorption dependence upon metal ion concentration could be fitted to a Langmiur isotherm model. Based on the results, the anaerobic granules treated with Ca appear to be a promising biosorbent for removal of heavy metals from wastewater due to its optimal uptake of heavy metals, its particulate shape, compact porous structure, excellent settling ability, and its high mechanical strength.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.     

Adsorption of Cr(VI) and As(V) ions by modified magnetic chitosan chelating resin

Cross-linked magnetic chitosan anthranilic acid glutaraldehyde Schiff's base (CAGS) was prepared for adsorption of both As(V) and Cr(VI) ions and their determination by ICP-OES. Prepared cross-linked magnetic CAGS was investigated by means of SEM, FTIR, wide angle X-ray diffraction (WAXRD) and TGA analysis. The adsorption properties of cross-linked magnetic CAGS resin toward both As(V) and Cr(VI) were evaluated. Various factors affecting the uptake behavior such as pH, temperature, contact time, initial concentration of metal ions, effect of other ions and desorption were studied. The equilibrium was achieved after about 110 min and 120 min for As(V) and Cr(VI), respectively at pH = 2. The adsorption kinetics followed the mechanism of the pseudo-second order equation for all systems studied, evidencing chemical sorption as the rate-limiting step of adsorption mechanism and not involving a mass transfer in solution. The equilibrium data were analyzed using the Langmuir, Freundlich, and Tempkin isotherm models. The best interpretation for the equilibrium data was given by Langmuir isotherm, and the maximum adsorption capacities were 58.48 and 62.42 mg/g for both Cr(VI) and As(V), respectively. Cross-linked magnetic CAGS displayed higher adsorption capacity for Cr(VI). The adsorption capacity of the metal ions increased with increasing temperature under optimum conditions in case of Cr(VI), but decreased in case of As(V). The metal ion-loaded cross-linked magnetic CAGS were regenerated with an efficiency of greater than 88% using 0.2 M sodium hydroxide (NaOH).     

Metal immobilisation by biofilms: Mechanisms and analytical tools

In biofilm environments, heavy metal and radionuclide pollutants are removed by a variety of mechanisms, including biosorption, precipitation as sulfides or phosphates and microbial reductive precipitation. Even if the elemental composition and localization of the precipitate trapped in the biofilm is well described thanks to spectroscopic and microscopic techniques, this review highlights that little is known about metal immobilisation mechanisms in microbial biofilms, i.e., mass transfer of metals, mechanisms involved in (bio)sorption and precipitation and the influence of physicochemical micro-environments within the biofilm matrix. The review shows the advantage of using a combination of different techniques to evaluate the fate of metals within microbial biofilms. By combining a variety of techniques (e.g., selective extraction, microscopy, spectroscopy and miniaturised sensors ...), it is possible to gain high-resolution structural and chemical information of biofilms on a level of the individual cell. This approach will facilitate the characterization of the metal immobilisation sites and the metal sorption and (bio)crystallisation mechanisms in biofilms. The results provided by the combination of these techniques will allow to predict the amount of metal accumulation in biofilms as well as their chemical speciation. This review demonstrates that an interdisciplinary approach is required to study metal fate within the biofilm matrix. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biosorption of Lead from Industrial Wastewater Using Chrysophyllum albidum Seed Shell

The shell of the seed of Chrysophyllum albidum carbon was used to adsorb lead (Pb) from aqueous solution, the sorption process with respect to its equilibria and kinetics as well as the effects of pH, contact time, adsorbent mass, adsorbate concentration, and particle size on adsorption were also studied. The most effective pH range was found to be between 4.5 and 5 for the sorption of the metal ion. The first-order rate equation by Lagergren was tested on the kinetic data and the adsorption process followed first-order rate kinetics. Isotherm data were analyzed for possible agreement with the Langmuir and Freundlich adsorption isotherms; the Freundlich and Langmuir models for dynamics of metal ion uptake proposed in this work fitted the experimental data reasonably well. However, equilibrium sorption data were better represented by Langmuir model than Freundlich. The adsorption capacity calculated from Langmuir isotherm was 72.1 mg Pb (II) g^{- 1} at initial pH of 5.0 at 30°C for the particle size of 1.00 to 1.25 mm with the use of 2.0 g/100 ml adsorbent mass. The structural features of the adsorbent were characterized by Fourier transform infrared (FTIR) spectrometry; the presence of hydroxyl, carbonyl, amide, and phosphate groups confirms the potential mechanism adsorption of the adsorbent. This readily available adsorbent is efficient in the uptake of Pb (II) ion in aqueous solution, thus, it could be an excellent alternative for the removal of heavy metals and organic matter from water and wastewater.     

Sorptive removal of Methylene blue from aqueous solution using palm kernel fibre: Effect of fibre dose

The use of palm kernel fibre, a readily available agricultural waste product for the sorption of Methylene blue from aqueous solution and the possible mechanism of sorption has been investigated at various fibre doses. The extent of dye removal and the rate of sorption were analyzed using two kinetic rate models (pseudo-first and pseudo-second-order kinetic models) and two diffusion models (intraparticle and external mass transfer models).

Analysis of the kinetic data at different sorbent dose revealed that the pseudo-first order kinetics fitted to the kinetic data only in the first 5 min of sorption and then deviated from the experimental data. The pseudo-second-order kinetic model was found to better fit the experimental data with high correlation coefficients at the various fibre dose used. The dye sorption was confirmed to follow the pseudo-second-order model by investigating the relationship between the amount of dye sorbed and the change in hydrogen ion concentration of the dye solution and also the dependence of dye uptake with solution temperature. It was found that the change in hydrogen ion concentration and increase in sorption temperature were directly related to the amount of dye sorbed, and activation energy was calculated to be −39.57 kJ/mol, indicating that the dye uptake is chemisorption, involving valence forces through sharing or exchange of electrons between sorbent and sorbate as covalent forces.

The intraparticle diffusion plots showed three sections indicating that intraparticle diffusion is not solely rate controlling. The intraparticle diffusion and mass transfer rate constants where observed to be well correlated with sorbent dose in the first 5 min of sorption, indicating sorption process is complex. It was found that at low sorbent dose the mass transfer is the main rate controlling parameter. However at high sorbent dose, intraparticle diffusion becomes rate controlling.     

The biosorption of heavy metals from aqueous solution by Spirogyra and Cladophora filamentous macroalgae

The aim of this research was to develop a low cost adsorbent for wastewater treatment. The prime objective of this study was to search for suitable freshwater filamentous algae that have a high heavy metal ion removal capability. This study evaluated the biosorption capacity from aqueous solutions of the green algae species, Spirogyra and Cladophora, for lead (Pb(II)) and copper (Cu(II)). In comparing the analysis of the Langmuir and Freundlich isotherm models, the adsorption of Pb(II) and Cu(II) by these two types of biosorbents showed a better fit with the Langmuir isotherm model. In the adsorption of heavy metal ions by these two types of biosorbents, chemical and physical adsorption of particle surfaces was perhaps more significant than diffusion and adsorption between particles. Continuous adsorption-desorption experiments discovered that both types of biomass were excellent biosorbents with potential for further development.