Biosorption of mercury by carboxymethylcellulose and immobilized Phanerochaete chrysosporium

Microchemical Journal 71 (2002) 73–81

Biosorption of mercury by carboxymethylcellulose and immobilized Phanerochaete chrysosporium b ¨ Genc¸ a, S. Bektasa,* A. Saglama, Y. Yalcinkaya , A. Denizlia, M.Y. Aricac, O. ¸ a

Department of Chemistry, Hacettepe University, Beytepe, Ankara, Turkey b Department of Biology, Hacettepe University, Beytepe, Ankara, Turkey c Department of Biology, Kirikkale University, Yahsihan, Kirikkale, Turkey

Received 30 May 2001; received in revised form 27 August 2001; accepted 14 September 2001

Abstract Phanerochaete chrysosporium basidiospores immobilized onto carboxymethylcellulose were used for the removal of mercury ions from aqueous solutions. The biosorption of Hg(II) ions onto carboxymethylcellulose and both immobilized live and heat-inactivated fungal mycelia of Phanerochaete chrysosporium was studied using aqueous solutions in the concentration range 30 – 700 mg ly1. The biosorption of Hg(II) ions by the carboxymethylcellulose and both live and heat-inactivated immobilized preparations increased as the initial concentration of mercury ions increased in the medium. Maximum biosorption capacity for immobilized live and heat-inactivated fungal mycelia of Phanerochaete chrysosporium was found to be 83.10 and 102.15 mg Hg(II) gy1, respectively, whereas the amount of Hg(II) ions adsorbed onto the plain carboxymethylcellulose beads was 39.42 mg gy1 . Biosorption equilibria were established in approximately 1 h and the correlation regression coefficients show that the adsorption process can be well defined by a Langmuir equation. Temperature changes between 15 and 45 8C did not affect the biosorption capacity. The effect of pH was also investigated and the maximum adsorption of Hg(II) ions onto the carboxymethylcellulose and both live and heat-inactivated immobilized fungal mycelia was observed at pH 6.0. The carboxymethylcellulose – fungus beads could be regenerated using 10 mM HCl, with up to 95% recovery. The biosorbents were used in three biosorption – desorption cycles and no significant loss in the biosorption capacity was observed. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: Hg(II); Carboxymethylcellulose; Biosorption; Phanerochaete chrysosporium

1. Introduction Mercury contamination of the environment is caused by both natural and manmade sources. Natural sources include volcanic action and erosion of mercury-containing sediments. Some of the ways in which humans contaminate the environ* Corresponding author. E-mail address: [email protected] (S. Bektas).

ment with mercury include: mining, transporting and processing mercury ores; dumping of industrial wastes into rivers and lakes; combustion of fossil fuels (e.g. the Hg content of coal is approx. 1 mg kgy1), pulp, and paper; use of mercury compounds as seed dressings in agriculture; and exhaust from metal smelters w1x. Similar to those of lead and cadmium, the ultimate effects of mercury in the body are inhibition of enzyme activity and cell

0026-265X/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 6 - 2 6 5 X Ž 0 1 . 0 0 1 4 2 - 4

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A. Saglam et al. / Microchemical Journal 71 (2002) 73–81

damage. Inhibition of a large variety of enzyme systems by mercury has been reported w2x. The particular reactivity of mercury with thiol ligands has further confirmed the selective affinity of this metal to react with the SH group, as shown with methylmercury in the following: RSHqCH3Hgq™ R–S–Hg–CH3qHq Mercury is known to affect the metabolism of mineral elements such as sodium and potassium by increasing the latter’s permeability. Mercury also inhibits active transport mechanisms through dissipation of the normal cation gradient; destroys the mitochondrial apparatus; causes swelling of cells, leading to lysis; decreases a- and g-globulins while increasing b-globulin, suggesting liver dysfunction; decreases DNA content in cells; and adversely affects chromosomes and mitosis, leading to mutagenesis w3x. The conventional treatments used to remove heavy metals from wastewaters are precipitation, coagulation, reduction and membrane processes, ion exchange and adsorption. However, the application of such processes is often restricted because of technical andy or economic constraints. For example, precipitation processes cannot guarantee the metal concentration limits required by regulatory standards and produce wastes difficult to treat; on the other hand, ion exchange and adsorption processes are very effective, but require expensive materials and difficult plant management w4x. In this respect, the search for a new, economical and effective heavy-metal adsorbent is focused on biomaterials, such as bacterial and algal biomasses w5x. The advantages of biosorption lie in both the good performance for metal removal, often comparable with their commercially available competitors (ion exchangers), and the cost-effectiveness, making use of algae and raw materials of fermentation and agricultural processes w6x. This aspect can play an important role in improving a zerowaste economic policy, especially in the case of the reuse of biomasses coming from food, pharmaceutical and wastewater treatments. Another biosorption advantage is the selectivity shown by some biomasses towards heavy metals, even in the presence of high concentrations of other ions, such as alkaline and alkaline earth

metals. When a proper immobilization or confinement technique is adopted, it is also possible to regenerate the biomasses and to reuse them. Sodium carboxymethylcellulose is a water-soluble polymer. The hydrophilic character of cellulose is obtained by carboxymethylation, and this also provides functional carboxylic groups on the cellulose derivative for cross-linking via trivalent metal ions. Carboxymethylcellulose can be simply converted into a hydrogel via chelation using salts of polyvalent cations, such as ferric and aluminum chlorides w7x. Biosorption of heavy metal ions is affected by many experimental factors, such as pH, ionic strength, biomass concentration, temperature and the presence of different metallic ions in solution. The variability of these factors in real wastewaters makes it necessary to know how they influence biosorption performance. As a consequence of the possible multiple interactions, the comprehension of biosorption phenomena is very complex and requires study of both the solution chemistry and the mechanisms of metal uptake w8x. The present study has the purpose of determining Hg(II) ion adsorption characteristics of carboxymethylcellulose and immobilized biomass of Phanerochaete chrysosporium, which gives good performance in heavy metal uptake. The effects of pH, temperature, adsorption time and initial metalion concentration were studied. In addition, equilibrium studies were performed with isotherm modeling. 2. Experimental 2.1. Microorganism and media White-rot basidiomycete, Phanerochaete chrysosporium ATCC 20696, was maintained by subculturing on malt-dextrose agar slants. Spore suspensions for immobilization were freshly prepared from 7-day-old cultures, grown on maltdextrose agar slants at 30 8C. The growth medium for Phanerochaete chrysosporium spores was prepared using deionized, double-distilled water and subsequently filter-sterilized; the final pH at 25 8C was adjusted to 4.5 (Table 1).

A. Saglam et al. / Microchemical Journal 71 (2002) 73–81 Table 1 Composition of growth medium (stock basal medium, SBM) Constituents

Concentration (gyl)

D-glucose Yeast extract MgSO4Ø7H2O CaCl2 NH4H2PO4 KH2PO4 MnCl2Ø4H2O CaCl2Ø6H2O FeSO4Ø7H2O ZnSO4Ø7H2O NaCl

10.0 0.1 0.5 0.1 0.5 0.2 1.0 0.1 1.0 1.4 0.5

2.2. Immobilization of Phanerochaete chrysosporium basidiospores The immobilization of Phanerochaete chrysosporium ATCC 20696 mycelia via entrapment was carried out as follows. Carboxymethylcellulose sodium salt (CMC; high viscosity, 1.0% in H2O at 25 8C giving 700–1500 mPa s; degree of substitution 0.60–0.95; Sigma Chemical Co, St Louis, USA) solution (2.0%, 50 cm3) was dissolved in distilled water and was then mixed with the macerated fungal mycelia (2.0 g in 50 cm3 of saline solution). The mixture was introduced into a 500cm3 0.2 M ferric chloride solution with a peristaltic pump (Cole Parmer model 7521-00, USA) through a nozzle (2 cm in length, 1.0-mm i.d.) and the solution was stirred to prevent aggregation of the mycelia-entrapped carboxymethylcellulose beads. The fungal mycelia-entrapped beads (;2 mm) were cured in this solution for 30 min and then washed twice with 200 cm3 of sterile distilled water. The beads with immobilized mycelia were then transferred to the growth medium (100 cm3) in a 250-cm3 flask and the flasks were incubated on an orbital shaker (150 rev. miny1) at 30 8C for 5 days. The mycelial growth inyon the beads was followed during the incubation period using a microscope. After 5 days of incubation, the carboxymethylcellulose beads with immobilized organisms were removed from the medium by filtration and washed twice with distilled water. The beads were then stored at 4 8C until use.

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2.3. SEM studies Samples of carboxymethylcellulose and immobilized Phanerochaete chrysosporium beads were coated under vacuum with a thin layer of gold and examined by scanning electron microscopy (JEOL, model JMS 5600). 2.4. Biosorption studies The biosorption of Hg(II) ions onto the plain carboxymethylcellulose beads and onto the immobilized Phanerochaete chrysosporium from aqueous solutions was investigated in batch biosorption–equilibrium experiments. The effect of the medium pH and the initial concentration of metal ions on the biosorption rate and capacity were studied. The effect of pH on the biosorption rate was investigated in the pH range 3.0–7.0. The suspensions were brought to the desired pH by adding HCl or NaOH at the beginning of the experiment, and were not controlled afterwards. Metal ion solutions (200 mg ly1) were prepared in 150 mM NaCl solution (25 ml) and fungus entrapped in carboxymethylcellulose was transferred into this medium and agitated magnetically at 400 rev. miny1. The effect of temperature on the biosorption capacity of the biosorbent was determined at pH 6.0 and a Hg(II) ion concentration of 200 mg ly1. The effect of the initial metal-ion concentration on the biosorption was studied at pH 6.0 as described above. 2.5. Analytical procedure Biosorption of mercury ions from aqueous solutions was studied in batch systems. The nitrate salt of Hg(II) ions was used. After the desired incubation period (approx. 120 min), the aqueous phases were separated from the biosorbents and the concentration of Hg(II) ions in these phases was determined. A Shimadzu model AA-6800 flame atomic absorption spectrophotometer equipped with MVU-1A mercury vapor unit was used throughout the study. Deuterium background correction was applied and the spectral slit width

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was 0.5 nm. The working currentywavelength values and the optimized experimental conditions were as follows: Working current Working wavelength SnCl2 concentration KMnO4 concentration H2SO4 concentration

6 mA 253.6 nm 1% (wyv) 0.5% (wyv) 5% (vyv)

The instrument response was periodically checked with metal-ion standard solutions. For each set of data reported, standard statistical methods were used to determine the mean values and standard deviations. Confidence intervals of 95% were calculated for each set of samples in order to determine the margin of error. The amount of metal ions adsorbed per unit of empty immobilized fungus carboxymethylcellulose preparations (mg metal ions gy1 dry beads) was obtained using the following expression: Qs

ŽCoyC. M

(1)

where Q is the amount of metal ions adsorbed onto the unit mass of the adsorbent (mg gy1), Co and C are the concentrations of the metal ions before and after biosorption (mg ly1), respectively, V is the volume of the aqueous phase (l) and M is the quantity of adsorbent (g). A known quantity of wet carboxymethylcellulose or immobilized fungal preparation was used in the adsorption tests. After the adsorption process, the adsorbents were dried in an oven at 50 8C overnight and the dry weight of the preparations was used in the calculations. 2.6. Desorptionyreuse In order to determine the reusability of the carboxymethylcellulose beads and immobilized fungal preparations, consecutive adsorption– desorption cycles were repeated three times using the same biosorbent. Desorption of Hg(II) ions was performed with 10 mM HCl solution. The carboxymethylcellulose and immobilized fungal preparations (approx. 0.10 g on wet basis) loaded with metal ions were placed in the desorption medium (25 ml) and stirred at 400 rev. miny1 for

60 min at 25 8C. The final Hg(II) ion concentrations in the aqueous phases were determined using AAS, as described above. The desorption ratio was calculated from the amount of metal ions adsorbed on the immobilized preparations and the final metal ion concentration in the adsorption medium using the following equation: desorption ratio amount of metal ions desorbed s amount of metal ions adsorbed (2) Percent desorption values were obtained by multiplying the above ratio by 100. 3. Results and discussion 3.1. Properties of the carboxymethylcellulosebased biosorbent system In the present work, carboxymethylcellulose beads were prepared by cross-linking with trivalent ferric ions. Fe(III) ions have strong affinity for electron-rich ‘bases’, such as carboxylic, phosphate and sulfate oxygen w9x. The presence of carboxylic groups on the carboxymethylcellulose molecules provides a binding side for Fe(III) ions. Crosslinking should be a combination of metal coordination and ion exchange interactions between the carboxylic oxygen of carboxymethylcellulose molecules and trivalent ferric ions. As a result of these interactions, carboxymethylcellulose droplets precipitated in bead form in aqueous ferric chloride solution. The water content of the carboxymethylcellulose beads was 92%. Their high water content made them highly permeable, which is advantageous for some biotechnological uses because of their enhanced degradability. Degradation of carboxymethylcellulose by microorganisms in nature makes it a potential candidate for various uses in which it can replace polymers of petroleum origin. This is also important because polymers of petroleum origin are non-degradable, making them a major cause of pollution. SEM micrographs of the plain carboxymethylcellulose beads and immobilized Phanerochaete chrysosporium beads are presented in Fig. 1a,b, respectively. The SEM micrograph of immobilized

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3.2. Biosorption rate Generally speaking, the uptake of heavy metal ions by microorganisms has often been observed to occur in two stages: an initial rapid uptake due to surface adsorption on the cell walls, and a subsequent slow uptake due to membrane transport of the metal ions into the cytoplasm of the cells. Surface adsorption is a physicochemical phenomenon. The cell walls of many microorganisms consist of polysaccharides, proteins and lipids, and therefore offer a host of functional groups capable of binding to heavy metals. These functional groups, such as amino, carboxylic, sulfhydryl, phosphate and thiol groups, differ in their affinity and specificity for metal binding. The equilibrium amount of a metal ion bound onto the cell surface would be determined by the relative affinity of the sites for toxic metals and other cations present and the residual concentrations of these metal ions not taken up in the solution. The surface-bound metal ion is then transported into the cytoplasm through the diffusion barrier presented by the cell membrane. Since a fixed cell biomass offers a finite number of surface binding sites, the initial uptake, being surface adsorption, would be expected to show saturation kinetics with increasing metal ion concentration.

Fig. 1. Backscattered electron image of (a) empty and (b) immobilized fungus carboxymethylcellulose beads.

fungus beads is completely different from the empty beads and revealed a uniform fungal growth on the bead surface, indicating that immobilization is not localized. This uniform distribution is an important criterion for the proper biosorption of heavy metal ions on the whole surface area of the immobilized fungus beads. Thus, immobilization of fungal cells can also provide additional advantages over freely suspended fungal cells.

Fig. 2. Adsorption rate of Hg(II) ions by plain carboxymethylcellulose (m), live (j) and heat-inactivated (●) Phanerochaete chrysosporium. Adsorption conditions: initial concentration of Hg(II) ions, 200 mgyl, pH 6.0; and temperature, 20 8C.

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Adsorption, together with membrane transport model, has previously been shown to be consistent with the uptake of single metal ions observed. As is evident from Fig. 2, the metal adsorption rate is high at the beginning, but plateau values are reached in 60 min. Data on the adsorption rates of heavy metal ions for various biosorbents have shown a wide range of adsorption time. For example, the biosorption equilibrium time of chromium (VI) on dead and immobilized biomass of Rhizopus arrhizus was 2 h w10x. The lead biosorption rate of Phanerochaete chrysosporium was fast and reached a saturation value within 2 h w11x. The lead biosorption equilibrium time on Aspergillus niger biomass was 5 h w12x. The biosorption of cadmium onto pretreated biomass of marine alga Durvillaea potatorum has been studied and the biosorption process was very fast, with 90% uptake taking place within 30 min w13x. Note that there are several parameters which determine the biosorption rate, such as: stirring rate; structural properties of the support and the biosorbent (e.g. protein and carbohydrate composition and surface charge density, topography and surface area); amount of sorbent; properties of the ions under study; initial concentration of ionic species; and the presence of other metal ions, which may compete with the ionic species of interest for the active biosorption sites. Therefore, it is difficult to compare the biosorption rates reported. 3.3. Effect of pH The increase in biosorption levels observed with increasing pH can be explained by the strong relation of biosorption to the number of surface negative charges, which depends on the dissociation of functional groups. It can also partly explain the low amounts of metal ions retained by the biosorbent at pH values below 4, because most functional groups are expected to dissociate only at neutral pH values. The occurrence of competition between protons and metal ions for the same sites should also be considered, particularly at low pH values, as proposed by several authors w14– 16x. In order to establish the effect of pH on the

Fig. 3. Effect of pH on the biosorption capacity of carboxymethylcellulose (m), live (j) and heat-inactivated (●) immobilized Phanerochaete chrysosporium beads for Hg(II) ions. Biosorption conditions: initial concentration of Hg(II) ions, 200 mgyl; volume of biosorption medium, 25 ml; temperature, 20 8C; and biosorption time, 60 min.

biosorption of Hg(II) ions onto the plain carboxymethylcellulose beads and immobilized Phanerochaete chrysosporium beads, batch equilibrium studies at different pH values were repeated in the range 3.0–7.0. Fig. 3 shows the effect of pH on biosorption. As is evident from the figure, the maximum adsorption of Hg(II) ions on the carboxymethylcellulose and immobilized live and heat-killed fungal mycelia was observed at pH 6.0. 3.4. Effect of temperature The effect of temperature on the biosorption of Hg(II) ions onto the plain carboxymethylcellulose beads and live and heat-killed immobilized preparations was studied between 15 and 45 8C at pH 6.0 and with 200 mgyl Hg(II) ion concentration. It was observed that temperature changes between 15 and 45 8C did not affect the biosorption capacity. 3.5. Effect of initial metal ion concentration Adsorption isotherms have commonly been used to describe experimental results for the uptake of metal ions by biomass, since the initial rapid uptake is believed to be due to binding of the metal ions onto the cell wall. Many studies have

A. Saglam et al. / Microchemical Journal 71 (2002) 73–81

Fig. 4. Biosorption capacity of plain carboxymethylcellulose (m), live (j) and heat-inactivated (●) Phanerochaete chrysosporium biomass for Hg(II) ions. Biosorption conditions: volume of the biosorption medium, 25 ml; pH 6.0; temperature, 20 8C; and biosorption time, 60 min.

shown that at low metal ion concentrations, the mass of the metal ion accumulated (per unit of cell mass) is directly proportional to the concentration of the ion in solution w17x. Central to the development of the adsorption plus membrane transport model is the basic assumption that a simple linear relationship exists between the concentration of the metal ions adsorbed on the surface of the cell and the metal ion concentration in solution. The metal-ion biosorption capacity of the carboxymethylcellulose and immobilized live and heat-inactivated Phanerochaete chrysosporium biomass is presented as a function of the equilibrium concentration of metal ions within the aqueous biosorption medium in Fig. 4. The initial concentration was changed in the range of 30– 700 mg ly1. Biosorption conditions are given in the figure legend. The amount of Hg(II) ions adsorbed per unit mass of the biosorbent (i.e. biosorption capacity) increased with the initial concentration of metal ions, as expected. In order to reach the plateau values which represent saturation of the active sites on the biosorbent, in other words to obtain the maximum biosorption capacity of the carboxymethylcellulose and immobilized fungus for Hg(II) ions, the initial concentration was increased up to 700 mg ly1. As is evident from Fig. 4, the

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amount of Hg(II) ions adsorbed on the plain carboxymethylcellulose beads was 39.42 mg gy1. Maximum biosorption capacity for immobilized live and heat-killed fungal mycelia of Phanerochaete chrysosporium was found to be 83.10 and 102.15 mg Hg(II) gy1, respectively. The order of affinity of the biosorbents for Hg(II) ions was: heat-inactivated Phanerochaete chrysosporium) live Phanerochaete chrysosporium)carboxymethylcellulose. The biosorption of Hg(II) on the heat-inactivated Phanerochaete chrysosporium was approximately 20% higher than that of the live organism. Thus, it is reasonable to assume that increased biosorption capacity is due to the changes in biosorptive characteristics of the fungus as a result of heat treatment. Heat treatment could erode microbial cell-surface integrity, causing the walls to become leaky, with a marked increase in the passive diffusion of metal ions into the interior parts of the cell walls w18x. Different sorbents (organic and biologic), having a wide adsorption-capacity range for heavy metal ions, have been reported. Hafez et al. reported that the biosorption capacity of Aspergillus flavus was 46 mg uranium gy1 dry biomass w19x. Chen and Wilson used a living E. coli strain for bioaccumulation of Hg(II) and the highest bioaccumulation level was obtained as 17.6 mg gy1 dry ¨ biomass w20x. Ozer et al. reported that the adsorption capacity of Rhizopus arrhizus and a living E. coli strain was 71 and 17.6 mg Hg(II) gy1, respectively w21x. Various sorbent materials, other than microbial mass, have also been used for removal of heavy metal ions from industrial waste, ranging from natural polysaccharide gels to coal and functionalized synthetic polymers. For example, Shah and Devi used a dithizone-anchored poly(vinyl pyridine) support and they reported a specific adsorption capacity of up to 144.42 mg Hg(II) gy1 w22x. Liu et al. achieved 72.21 mg Hg(II) gy1 adsorption capacity with N-hydroxymethyl thioamide resin w23x. Cestari and Airoldi found 186.55 mg Hg(II) gy1 with 3-trimethoxysilyl-1-propanethiol immobilized on silica w24x. Jyo et al. reported 40.12 mg Hg(II) gy1 with phosphoric acid-treated poly(glycidylmethacrylate –co-divinyl-benzene) beads w25x. Say et al. used dithiocarbamate-incorporated monosize polysty-

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Table 2 Isotherm model constants and correlation regression coefficients for biosorption of Hg(II) ions from aqueous solution Biosorbent

CMC Live P. chrysosporium Heat-inactivated P. chrysosporium

Langmuir

Freundlich

aL yKL (mgyg)

KL (=104 molyl)

R2

a

b

R2

46.8 124.9 158.6

5.06 9.88 14.08

0.9996 0.9993 0.9995

6.78 2.09 4.88

2.98 1.65 0.94

0.9854 0.9712 0.9830

rene microspheres for adsorption of organomercury species, with a maximum adsorption capacity reported as 122.36 mg gy1 for CH3HgCl, 114.34 mg gy1 for C2H5HgCl and 20.06 mg gy1 for C6H5HgCl w26x. 3.6. Equilibrium studies

KLCe 1qaLCe

(3)

The constants KL and aL are the characteristics of the Langmuir equation and can be determined from a linearized form of the above equation: Ce 1 aL s q Ce qe KL KL

qesaCeb

(4)

Therefore, a plot of Ce yqe vs. Ce gives a straight line of slope aL yKL and intercept 1yKL. The constant KL is the Langmuir equilibrium constant and the ratio aL yKL gives the theoretical monolayer saturation capacity. The Langmuir equation is applicable to homogeneous sorption, where each metal ion–microorganism sorption process has equal sorption activation energy. The Langmuir equation obeys Henry’s Law at low concentrations. The Freundlich expression is an empirical equation based on sorption on a heterogeneous surface.

(5)

and the equation may be linearized by taking logarithms: lnqesblnCeqlna

In order to optimize the design of a sorption system to remove metal ions, it is important to establish the most appropriate correlation for the equilibrium curves. Two isotherm equations have been tested in the present study, namely Langmuir and Freundlich. The most widely used isotherm equation for modeling equilibrium data is the Langmuir equation, which for dilute solutions may be represented as: qes

The Freundlich equation is commonly presented as:

(6)

Therefore, a plot of lnqe vs. lnCe enables the constant a and exponent b to be determined. The Langmuir and Freundlich constants, along with the correlation coefficients (R 2), have been calculated from the corresponding plots for biosorption of Hg(II) ions on the biosorbents and the results are presented in Table 2. The correlation regression coefficients show that the adsorption process can be well defined by Langmuir equation. The Langmuir fit is considered to be evidence that sorption stops at one monolayer, consistent with specific and strong sorption onto specific sites. Because the exchange reaction between surface sites and previously adsorbed ions is of only a monolayer or less, there is an accumulation of matter at the solid–solution interface, without the creation of a three-dimensional structure. 3.7. Desorption and reuse More than 95% of the metal ions adsorbed were desorbed from the biosorbents with 10 mM HCl solution. In order to show the reusability of the biosorbents, an adsorption–desorption cycle of metal ions was repeated three times using the same preparations. The adsorption capacity did not significantly change (only a maximum 3% change was observed with the biosorbent tested) during the repeated adsorption–desorption operations.

A. Saglam et al. / Microchemical Journal 71 (2002) 73–81

These results showed that carboxymethylcellulose beads and fungus-entrapped biosorbents could be repeatedly used in heavy-metal adsorption studies without any detectable losses in their initial adsorption capacity. 4. Conclusion In this study, carboxymethylcellulose and immobilized Phanerochaete chrysosporium biomass were tested as mercury biosorbents and performance was examined as a function of the operating conditions, in particular the equilibrium pH and initial metal-ion concentration. The experimental evidence shows a strong effect of the operating conditions on biosorption performance and demonstrates the necessity of knowledge of the biosorption phenomenon.

w7 x w8 x w9 x w10x w11x w12x w13x w14x w15x w16x w17x

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