Accumulation and removal of heavy metal ions by insolubilized-DNA and its interaction.

DNA was immobilized onto a porous glass bead by a treatment with UV irradiation. The immobilized DNA was insoluble in water and used for accumulation of heavy metal ion. When DNA-immobilized glass bead was added into aqueous solution containing heavy metal ions, such as Hg2+, Cd2+, Pb2+, Zn2+, Cu2+ and Fe3+, the concentration of these metal ions in the solution was decreased. However, the concentration of Mg2+ in the solution was not affected by the addition of the DNA-immobilized glass bead. These results suggested that UV-irradiated DNA selectively accumulated heavy metal ions.     

Enterovirus 71 adsorption on metal ion-composite chitosan beads

In this study, we developed composite chitosan beads combining various metal ions, including Ni(2+), Cu(2+), Zn(2+), and Fe(2+), for direct adsorption of enterovirus 71 (EV71). The metal-ion species had significant effects on the adsorption capacity of beads. Among these metal ion-composite chitosan beads, Ni(2+)-chitosan beads exhibited the best adsorption capacity of EV71. Using a concentration of 0.01-M Ni(2+) was found to best provide for bead formation and EV71 adsorption. The adsorption of EV71 for Ni(2+)-chitosan beads at neutral or alkaline pH was favored. Under a competitive condition with albumin proteins, Ni(2+)-chitosan beads exhibited significant capacity of EV71 adsorption in culture media. The adsorption of EV71 on the Ni(2+)-chitosan beads was attributed to the strong binding between Ni(2+) ions chelated to the surface amino acid of EV71 capsids and Ni(2+) ions chelated on the chitosan materials. Moreover, the adsorbed EV71 retained its antigenicity and infectivity after desorption. The Ni(2+)-chitosan beads exhibit a promising application to EV71 adsorption and removal.     

A systematic study of liposome and proteoliposome reconstitution involving Bio-Bead-mediated Triton X-100 removal

Equilibrium and kinetic aspects of Triton X-100 adsorption onto hydrophobic Bio-Beads SM2 were investigated in detail using the batch procedure originally described by Holloway, P.W. (1973) Anal. Biochem. 53, 304-308. The results demonstrated the importance of the initial detergent concentration, the amount of beads, the commercial source of the detergent, the temperature and the presence of phospholipids in determining the rates of Triton X-100 adsorption onto Bio-Beads. One of the main findings was that Bio-Beads allowed the almost complete removal of Triton X-100, whatever the initial experimental conditions. It was shown that monomeric as well as micellar detergent could be adsorbed and that a key factor in determining the rate of detergent removal was the availability of the free bead surface. Rates of detergent removal were found to be linearly related to the amount of beads even for bead concentrations above those sufficient to remove all the detergent initially present. Adsorptive capacity of phospholipids onto Bio-Beads SM2 was also analyzed and found to be much smaller (2 mg lipid per g of wet beads) than that of Triton X-100 (185 mg TX 100 per g of wet beads). A more general aspect of this work was that the use of Bio-Beads SM2 provided a convenient way for varying and controlling the time course of Triton X-100 removal. The method was further extended to the formation of liposomes from phospholipid-Triton X-100 micelles and the size of the liposomes was found to be critically dependent upon the rate of detergent removal. A general procedure was described to prepare homogeneous populations of vesicles. Freeze-fracture electron microscopy and permeability studies indicated that the liposomes thus obtained were unilamellar, relatively large and impermeable. Noteworthy, this new procedure was shown to be well suited for the reconstitution of different membrane transport proteins such as bacteriorhodopsin, Ca2(+)-ATPase and H(+)-ATPase.     

Trypsin immobilization by direct adsorption on metal ion chelated macroporous chitosan-silica gel beads

Silica gel bead coated with macroporous chitosan layer (CTS-SiO₂) was prepared, and the metal immobilized affinity chromatographic (IMAC) adsorbents could be obtained by chelating Cu²⁺, Zn²⁺, Ni²⁺ ions, respectively on CTS-SiO₂, and trypsin could be adsorbed on the IMAC adsorbent through metal–protein interaction forces. Batch adsorption experiments show that adsorption capacity for trypsin on these IMAC adsorbent variated with change of pH. The maximal adsorption reached when the solution was in near neutral pH in all three IMAC adsorbents. Adsorption isothermal curve indicated that maximal adsorption capacity could be found in the Cu²⁺-CTS-SiO₂ with the value of 4980 ± 125 IU g⁻¹ of the adsorbent, while the maximal adsorption capacity for trypsin on Zn²⁺ and Ni²⁺ loaded adsorbent was 3762 ± 68 IU g⁻¹ and 2636 ± 53 IU g⁻¹, respectively. Trypsin immobilized on the IMAC beads could not be desorbed by water, buffer and salt solution if the pH was kept in the range of 5–10, and could be easily desorbed from the IMAC beads by acidic solution and metal chelating species such as EDTA and imidazole. The effect of chelated metal ions species on CTS-SiO₂ beads on the activity and stability of immobilized trypsin was also evaluated and discussed. Trypsin adsorbed on Zn-IMAC beads retained highest amount of activity, about 78% of total activity could be retained. Although the Cu-IMAC showed highest affinity for trypsin, only 25.4% of the calculated activity was found on the beads, while the activity recovery found on Ni-IMAC beads was about 37.1%. A remarkable difference on stability of trypsin immobilized on three kinds of metal ion chelated beads during storage period was also found. Activity of trypsin on Cu-IMAC decreased to 24% of its initial activity after 1-week storage at 4 °C, while about 80% activity was retained on both Ni-IMAC and Zn-IMAC beads. Trypsin immobilized on Zn-CTS-SiO₂ could effectively digest BSA revealed by HPLC peptide mapping.     

Lipid-protein interaction at solid-water interface. Adsorption of human apo-high density lipoprotein to amphiphilic interfaces

Hydrophobic glass beads with well characterized physical properties were used as a model system to study at the amphiphilic interface the properties of apolipoproteins A-I and A-II from human serum high density lipoproteins. In this study, spherical glass beads with known diameter were coated covalently with a film of silicone to varying surface density. The decrease in surface tension induced by coating was directly related to the increase in silicone film density and likely to the hydrophobicity of the glass surface. The adsorption of apo-A-I and apo-A-II to the hydrophobic glass bead surface was determined by following the decrease of 1) the radioactivity of preparations of 125I-iodinated proteins from the solution, 2) the UV absorbance of the solution at 206 nm, and 3) the fluorescence emitted by the complex formed between free protein and Fluram II in solution. All of the three measurements gave identical results. Both proteins adsorbed rapidly and reversibly to the hydrophobic glass surface. The adsorption isotherms followed the Langmuir equation with apo-A-II showing a higher surface affinity; delta Gaff = RT ln Kd has a value of -9.1 kcal/mol and -10.5 kcal/mol for apo A-I and apo A-II, respectively. The addition of canine serum high density lipoprotein (HDL) to the above system caused a rapid desorption of apolipoproteins from the beads into the aqueous phase and adsorption onto the HDL surface with no detectable structural changes of this lipoprotein. The results indicate that apo-A-I and apo-A-II can reversibly be adsorbed at a solid hydrophobic surface and that these apoproteins are capable of moving into a HDL particle if added to the system via a solution phase. The data suggest that the rate limiting aspect of the desorption-adsorption processes is the concentration of the apoproteins in solution.     

Transport limitation of chlorine disinfection of Pseudomonas aeruginosa entrapped in alginate beads

An artificial biofilm system consisting of Pseudomonas aeruginosa entrapped in alginate and agarose beads was used to demonstrate transport limitation of the rate of disinfection of entrapped bacteria by chlorine. Alginate gel beads with or without entrapped bacteria consumed chlorine. The specific rate of chlorine consumption increased with increasing cell loading in the gel beads and decreased with increasing bead radius. The value of an observable modulus comparing the rates of reaction and diffusion ranged from less than 0.1 to 8 depending on the bead radius and cell density. The observable modulus was largest for large (3-mm-diameter) beads with high cell loading (1.8 x 10(9) cfu/cm(3)) and smallest for small beads (0.5 mm diameter) with no cells added. A chlorine microelectrode was used to measure chlorine concentration profiles in agarose beads (3.0 mm diameter). Chlorine fully penetrated cell-free agarose beads rapidly; the concentration of chlorine at the bead center reached 50% of the bulk concentration within approximately 10 min after immersion in chlorine solution. When alginate and bacteria were incorporated into an agarose bead, pronounced chlorine concentration gradients persisted within the gel bead. Chlorine did gradually penetrate the bead, but at a greatly retarded rate; the time to reach 50% of the bulk concentration at the bead center was approximately 46 h. The overall rate of disinfection of entrapped bacteria was strongly dependent on cell density and bead radius. Small beads with low initial cell loading (0.5 mm diameter, 1.1 x 10(7) cfu/cm(3)) experienced rapid killing; viable cells could not be detected (<1.6 x 10(5) cfu/cm(3)) after 15 min of treatment in 2.5 mg/L chlorine. In contrast, the number of viable cells in larger beads with a higher initial cell density (3.0 mm diameter, 2.2 x 10(9) cfu/cm(3)) decreased only about 20% after 6 h of treatment in the same solution. Spatially nonuniform killing of bacteria within the beads was demonstrated by measuring the transient release of viable cells during dissolution of the beads. Bacteria were killed preferentially near the bead surface. Experimental results were consistent with transport limitation of the penetration of chlorine into the artificial biofilm arising from a reaction-diffusion interaction. The methods reported here provide tools for diagnosing the mechanism of biofilm resistance to reactive antimicrobial agents in such applications as the treatment of drinking and cooling waters. (c) 1996 John Wiley & Sons, Inc.     

Solid phase extraction of the zwitterionic detergent chaps

Multiple techniques for solid phase adsorption of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) were evaluated. Both the porous polystyrene divinylbenzene matrices (BioBeads SMTM) and Extracti GelTM D reduced CHAPS to significantly below its critical micellar concentration while Extracti-GelTM removed CHAPS to below detectable limits. Bio-Bead extraction of CHAPS correlated with the surface area of the bead type. SM-16 beads, with the largest effective surface area, removed nearly 97% of the detergent. For a given amount of detergent and mass of Bio-Beads, the ratio of sample to total bead volume significantly affected CHAPS adsorption. Total protein recovery with the Extracti-GelTM was approximately 97%. Protein recovery in the samples treated with Bio-Beads varied from 56-95%. Chromatographic rather than batch processing yielded optimum recoveries. CHAPS can be effectively removed from dilute protein solutions by solid phase adsorption and this technique offers significant advantages over standard dialysis or gel filtration methods.     

Decolorization of azo dye using PVA-immobilized microorganisms

A microbial consortium having a high capacity for rapid decolorization of azo dye (RED RBN) was immobilized by a phosphorylated polyvinyl alcohol (PVA) gel. The immobilized-cell beads exhibited a color removal capability of 75%, even at a high concentration of RED RBN (500 mg l(-1)) within 12 h using flask culture. The continuous operation was conducted at a hydraulic retention time (HRT) of 5-20 h in which the dye loading rate ranged from 240 to 60 mg dye h(-1). A removal efficiency exceeding 90% was obtained at the HRT higher than 10 h. No recognizable destruction of bead appearance was observed in the 6-month operation. Examination of the mechanism of the decolorization process by cell beads indicated that it proceeded primarily by biological decolorization associated with partial adsorption of the dye onto the entrapped cells and gel matrix. Microscopic observation revealed that the microbial consortium contained in the gel beads was at least made up of three kinds of bacterial species. From the economical viewpoint, alternative cheaper nitrogen sources such as fish meal, soybean meal, pharmamedia and vita yeast powder were examined.     

Regulation of helper cell activity by specifically adsorbable T lymphocytes.

Mice immunized with soluble proteins such as human serum albumin (HSA) or ovalbumin (OA) develop in their spleens antigen-specific T and B lymphocytes. These populations of lymphocytes can be separated from each other by different means; e.g. treatment with anti-theta-antiserum and complement removes selectively T lymphocytes, whereas passage through glass bead columns coated with mouse immunoglobulin (Ig): anti-Ig complexes creates a relatively pure population of T lymphocytes. During the course of such separation studies it was observed that the helper capacity of HSA (or OA) immune mouse spleen cells after Ig:anti-Ig column passage frequently was higher than expected from the enrichment in theta-positive cells. In addition, after adsorption onto antigen coated Bio-Gel beads this effect was even more pronounced, i.e., and increase in the relative helper capacity of about 3 or 4 times compared with an increase in the content of theta-positive cells from about 30% to 40 to 50% after adsorption. The present results will demonstrate that the increased helper capacity was a specific phenomenon which was regulated by theta-positive cells. The regulatory cells specifically adsorbed onto antigen-coated Bio-Gel beads have not been successfully eluted by EDTA or excess-free antigen so far, and they were still adsorbed after pre-incubation with anti-Ig antibodies under conditions where specific B lymphocyte adsorption was almost prevented.     

Removal and biodegradation of nonylphenol by immobilized Chlorella vulgaris

The removal and biodegradation of nonylphenol (NP) by alginate-immobilized cells of Chlorella vulgaris were compared with their respective free cultures. The effects of four cell densities of 10(4) per algal bead were investigated, as were the four algal bead concentrations, with regard to the removal and biodegradation of NP. Although immobilization significantly decreased the growth rate and NP's biodegradation efficiency of C. vulgaris, NP removal over a short period was enhanced. The NP removal mechanism by immobilized cells was similar to that by free cells, including adsorption onto alginate matrix and algal cells, absorption within cells and cellular biodegradation. The optimal cell density and bead concentration for the removal and biodegradation of NP was 50-100×10(4) cells algal bead(-1) and 2-4 beads ml(-1) of wastewater, respectively. These results demonstrated that immobilized C. vulgaris cells under optimal biomass and photoautotrophic conditions are effective in removing NP from contaminated water.     

Novel method for cell immobilization and its application for production of oligosaccharides from sucrose

AIMS: The purpose of the present investigation was to develop a novel method for cell immobilization. METHODS AND RESULTS: Aureobasidium pullulans cells were mixed with an alginate solution, and the mixture was extruded to form small gel beads as hydrated-immobilized cells. The beads were then placed at -15 degrees C for 6-24 h to induce freeze-dehydration. The freeze-dehydration resulted in shrinkage of beads as a result of water removal reducing bead volume by 82% and bead weight by 85%. The dehydrated beads were successfully used for the production of fructo-oligosaccharides in a model reactor system. CONCLUSIONS: Dehydrated beads may provide some commercial advantages over conventional immobilized cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that bioreactor performance can be improved up to two times by the use of the dehydrated beads.     

Equilibrium and kinetics studies of adsorption of copper (II) on chitosan and chitosan/PVA beads

The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.     

Measurement of phagocytosis using fluorescent latex beads

Fluorescent monodisperse latex beads and a computer-centered spectrofluorimeter were used to devise a sensitive new assay for phagocytosis. LM fibroblasts, a transformed cell line with a high endocytic rate, were exposed to fluoresbrite beads and the following parameters were investigated: incubation time, incubation temperature and bead/cell ratio. The bead uptake was linear for 60 min over a wide range of bead/cell ratios up to 130 beads/cell. Phagocytosis was inhibited at 4 degrees C, by incubation in the presence of colchicine, and by glucose deprivation. Scanning and transmission electron microscopy were used to confirm that at 37 degrees C both bead adsorption and internalization occurred while at 4 degrees C only bead adsorption but not endocytosis occurred. Large bead sizes (0.86 and 1.72 micrometer diameter) were most useful due to higher fluorescence and higher signal to noise ratios than smaller beads (0.25 and 0.57 micrometer diameter). Beads (0.86 micrometer diameter) were taken up at a rate of 4.4 beads/cell/h at 37 degrees C when a bead/cell ratio of 70 was used. The uptake was zero when assayed at zero time. These criteria establish that fluoresbrite beads provide a useful new fluorimetric assay for phagocytosis.     

Bacterial cellulose-chitosan composite hydrogel beads for enzyme immobilization

In this work, we report the preparation of bacterial cellulose (BC)-chitosan composite hydrogel beads by co-dissolution of BC and chitosan in 1-ethyl-3-methylimidazolium acetate and subsequent reconstitution with distilled water. The BC-chitosan hydrogel beads were used as enzyme supports for immobilizing Candida rugosa lipase by physical adsorption and covalent cross-linking. BC-chitosan hydrogel beads immobilized lipase more efficiently than microcrystalline cellulose (MCC)-chitosan hydrogel beads. The amount of protein adsorbed onto BCchitosan beads was 3.9 times higher than that adsorbed onto MCC-chitosan beads, and the catalytic activity of lipase was 1.9 times higher on the BC-chitosan beads. The lipase showed the highest thermal and operational stability when covalently cross-linked on BC-chitosan hydrogel beads. The half-life time of the lipase cross-linked on BC-chitosan bead at 60°C was 22.7 times higher than that of free lipase. Owing to their inherent biocompatibility and biodegradability, the BC-chitosan composite hydrogel beads described here could be used to immobilize proteins for various biomedical, environmental, and biocatalytic applications.     

Preparation of silica encapsulated quantum dot encoded beads for multiplex assay and its properties

Novel -COOH modified polystyrene beads were prepared by sulfonation grafting, and the surface area and pore volume are greatly improved in comparison with the swelling-treated beads. The optimization coating time is 4 h, and the corresponding -COOH content is approximately 2.1 mmol/g. The scanning electron microscope results show that the silica particles deposited on the beads and formed a silica shell that decreases the leakage of quantum dots (QDs) preferably and improves the bar code stability greatly. The anti-photobleaching of silica-coated beads was studied systemically, and the results show that the half-decay time (t1/2) of the coated beads increases to 537 s--seven times longer than that of the uncoated ones. Further DNA probe hybridization experiments indicated that the coding signal and target signal can be detected simultaneously and that the assays based on these probe-conjugated silica/QD/polystyrene beads have good specificity and sensitivity that can detect a concentration as low as 0.01 microg/ml target DNA in denatured calf thymus DNA solution, indicating that it is feasible to use this kind of bead for multiplex analysis.     

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.     

Effective Bead Preparation of Coimmobilized Methanogenic and Methanotrophic Bacteria for Tetrachloroethene Degradation

Three types of coimmobilized methanogenic and methanotrophic bacterial beads – Ca-alginate, Ba-alginate, and Ca-alginate chitosan – were used for tetrachloroethene (PCE) degradation. For the purpose of effective preparation of coimmobilized bacterial beads, the diameter and broken-loading of beads were measured. The activity tests to find the optimal bacteria concentration in the bead were performed. It was found that Ba-alginate beads had superiority in bacterial growth and the degree of strength of beads from the diameter and broken-loading tests. Also, it was shown that it is most effective to add 200 mL of methanogens into 500 mL of 2% alginate solution and 20 mL of methanotrophs into 500 mL to 2% alginate solution. When methanogens and methanotrophs were applied with the Ba-alginate bead in the actual dechlorination of PCE, the biological PCE dechlorination rate was 92%, and there was highly effective degradation of PCE based on the coimmobilized bead. Additionally, relation to the diameter (X) and broken-loading (Y) of the Ba-alginate bead was derived following equation, Y = 438.02 exp(–1.4815 X).     

Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies

The biosorption process for removal of lead, cadmium, and zinc by Citrobacter strain MCM B-181, a laboratory isolate, was characterized. Effects of environmental factors and growth conditions on metal uptake capacity were studied. Pretreatment of biomass with chemical agents increased cadmium sorption efficiency; however, there was no significant enhancement in lead and zinc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was found to be influenced by the pH of the solution, initial metal concentration, biomass concentration, and type of growth medium. The metal sorption process was not affected by the age of the culture or change in temperature. Equilibrium metal sorption was found to fit the Langmuir adsorption model. Kinetic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. The presence of cations reduced lead, zinc, and cadmium sorption to the extent of 11. 8%, 84.3%, and 33.4%, respectively. When biomass was exposed to multimetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < Cu2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads prepared by immobilizing the Citrobacter biomass in polysulfone matrix exhibited high metal loading capacities. A new mathematical model used for batch kinetic studies was found to be highly useful in prediction of experimentally obtained metal concentration profiles as a function of time. Metal desorption studies indicated that Citrobacter beads could, in principle, be regenerated and reused in adsorption-desorption cycles. In an expanded scale trial, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.     

Electrostatically mediated interactions between cationic lipid-DNA particles and an anionic surface.

In an effort to model the interaction of lipid-based DNA delivery systems with anionic surfaces, such as a cell membrane, we have utilized microelectrophoresis to characterize how electrokinetic measurements can provide information on surface charge and binding characteristics. We have established that cationic lipids, specifically N-N-dioleoyl-N,N-dimethylammonium chloride (DODAC), incorporated into liposomes prepared with 1, 2-dioleoyl-i-glycero-3-phosphoethanolamine (DOPE) or 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 50 mol%, change the inherent electrophoretic mobility of anionic latex polystyrene beads. Self-assembling lipid-DNA particles (LDPs), prepared at various cationic lipid to negative DNA phosphate charge ratios, effected no changes in bead mobility when the LDP charge ratio (+/-) was equal to or less than 1. Increasing the LDP concentration in a solution of 0.1% (w/v) anionic beads resulted in a charge reversal effect when a net charge of LDP to total bead charge ratio (+/-) of 1:1 was observed. LDP formulations, utilizing either DOPE or DOPC, showed similar titration profiles with a charge reversal observed at a 1:1 net LDP to bead charge ratio (+/-). It was confirmed through centrifugation studies that the DNA in the LDP was associated with the anionic latex beads through electrostatic interactions. LDP binding, rather than the binding of dissociated cationic lipids, resulted in the observed electrophoretic mobility changes of the anionic latex beads.     

The influence of the degree of cross-linking on the adsorption properties of chitosan beads

The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pKa varied in the range of 90-96% and 4.3-6.0, respectively, and were found to decrease with increasing DCL (0.0-34.0%). A pH-model, which described the reversibility of the metal adsorbed onto the beads, was used to predict the equilibrium properties of copper adsorption onto the cross-linked beads. The model accounts for the effect of pH and the important model parameters, the equilibrium adsorption constant (Kads) and to a lesser extent the adsorbent adsorption capacity (qmax) showed to decrease with the DCL. The adsorbent capacity and the adsorption constant were determined as 3.8-5.0mmol/g chitosan and (9-90)x10(-4), respectively. The adsorption kinetics could be described using a shrinking core model and the effective diffusion coefficient (Deff) was determined as (8.0-25.8)x10(-11)m2/s. It was found that Deff decreases with the DCL mainly due to the decreased in water content of the beads at high DCL.