Nonlinear modelisation of heavy metal removal from aqueous solution using Ulva lactuca algae

After extensive analysis, Ulva lactuca dried algae, collected from the Monastir coastal zone, was proven to be successful as an adsorbent for the removal of certain inorganic pollutants. The main objective of this study was the nonlinear modeling of heavy metal removal from an aqueous solution, using a freely available and well analyzed biomaterial, as well as the evaluation of its efficacy on various metal ion sorptions. Although relatively low specific surface area, compared to more conventional adsorbents, the selected biomaterial displays very interesting retention capacities when used with aqueous inorganic pollutants. The pseudo, first and second-order kinetic models were used to investigate the kinetic retention mechanism. Assuming the nonlinear form, the results indicate that the retention mechanism is diffusion controlled. Concerning the heavy metal uptake capacity, it was found that the selected biomaterial has a retention capacity of 67 mg g⁻¹ of Ni(II), 112 mg g⁻¹ of Cu(II), 127 mg g⁻¹of Cd(II) and 230 mg g⁻¹ of Pb(II).     

Sorption of heavy metals from electroplating effluent using immobilized biomass Trichoderma viride in a continuous packed-bed column

The sorption of heavy metals ions by immobilized Trichoderma viride biomass in a packed-bed column was studied. Fungal biomass T. viride was immobilized to Ca-alginate used for removal of Cr(VI), Ni(II) and Zn(II) ions from synthetic solutions and electroplating effluent. The experiments were conducted to study the effect of important design parameters such as bed height, flow rate and initial concentration of metal ions. The maximum sorption capacity was observed at flow rate 5 ml/min, bed height 20 cm and metal ions concentration 50 mg/L with immobilized biomass. Whereas, breakthrough time and saturation time decreased with increase flow rate and metal ions concentration and an inverse condition was found in bed height. The bed depth service time (BDST) Adams-Bohart model was used to analyze the experimental data. The regeneration efficiency was observed 40.1%, 75% and 53% for Cr(VI), Ni(II) and Zn(II) without any significant alteration in sorption capacity after 5th sorption-desorption cycles.     

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.     

Study of the biosorption of different heavy metal ions onto Kraft lignin

The ability of Kraft lignin, a waste product of paper production, for removing copper, zinc, cadmium and chromium ions from water was investigated. The studies were conducted by a batch method to determine equilibrium parameters. The adsorbed heavy metal ions followed the order: Cr(VI) ? Cd(II) > Cu(II) > Zn(II). The influence of other ions such as Ni(II), Cd(II) and Pb(II), on Cu(II) adsorption by Kraft lignin was evaluated. Obtained results support the idea that adsorption behaviour of heavy metal ions have to be perceived from the aspect of possible influence of interfering ion species.     

Biosorption of heavy metals from aqueous solutions with tobacco dust

A typical lignocellulosic agricultural residue, namely tobacco dust, was investigated for its heavy metal binding efficiency. The tobacco dust exhibited a strong capacity for heavy metals, such as Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II), with respective equilibrium loadings of 39.6, 36.0, 29.6, 25.1 and 24.5 mg of metal per g of sorbent. Moreover, the heavy metals loaded onto the biosorbent could be released easily with a dilute HCl solution. Zeta potential and surface acidity measurements showed that the tobacco dust was negatively charged over a wide pH range (pH > 2), with a strong surface acidity and a high OH⁻ adsorption capacity. Changes in the surface morphology of the tobacco dust as visualized by atomic force microscopy suggested that the sorption of heavy metal ions on the tobacco could be associated with changes in the surface properties of the dust particles. These surface changes appeared to have resulted from a loss of some of the structures on the surface of the particles, owing to leaching in the acid metal ion solution. However, Fourier transform infrared spectroscopy (FTIR) showed no substantial change in the chemical structure of the tobacco dust subjected to biosorption. The heavy metal uptake by the tobacco dust may be interpreted as metal–H ion exchange or metal ion surface complexation adsorption or both.     

Beneficial and preventive effect of chitin nanofibrils in a dextran sulfate sodium-induced acute ulcerative colitis model

Chitin nanofibrils, which are prepared from dried crab shells by a grinding method, are newly developed natural materials with uniform widths of approximately 10-20 nm. The bioactivities of chitin nanofibrils have not been investigated. In this study, we examined the preventive effects of chitin nanofibrils in a mouse model of dextran sulfate sodium (DSS)-induced acute ulcerative colitis. The results indicated that chitin nanofibrils improved clinical symptoms and suppressed ulcerative colitis. Furthermore, chitin nanofibrils suppressed myeloperoxidase activation in the colon and decreased serum interleukin-6 concentrations. Conversely, chitin powder did not suppress DSS-induced acute ulcerative colitis. Our results suggested that chitin nanofibrils have potential as a functional substance for inflammatory bowel disease patients.     

Synthesis of γ-cyclodextrin/chitosan composites for the efficient removal of Cd(II) from aqueous solution

The synthesis of chitosan-graft-γ-cyclodextrin (Ch-g-γ-CD) using persulfate/ascorbic acid redox system was done and characterized by FTIR, XRD, TGA and SEM/EDX. The optimum yield of the copolymer was obtained using 16 × 10⁻³ M γ-cyclodextrins (γ-CD), 2.8 × 10⁻² M ascorbic acid (AA), 1.8 × 10⁻² M K₂S₂O₈ and 0.1 g chitosan in 25 mL of 2% aqueous formic acid at 45 ± 0.2 °C. The highest percent grafting samples were evaluated for cadmium metal ion (Cd(II)) removal from the aqueous solutions where the sorption capacities were found proportional to the grafting extent. The sorption was pH and concentration dependent where, pH = 8.5 was found to be the optimum value. The adsorption data were modeled using Langmuir and Freundlich isotherms. The equilibrium data followed the Langmuir isotherm model with maximum sorption capacity of 833.33 mg/g. The influence of electrolytes, sodium chloride (NaCl) and sodium sulphate (Na₂SO₄) on Cd(II) uptake was also studied. Desorption of the cadmium loaded Ch-g-γ-CD was accomplished with 0.01 N H₂SO₄. The adsorbent exhibited high reusability and could be successfully recycled for nine cycles where in the ninth cycle 27% adsorption was feasible.     

Removal of perfluorooctane sulfonate from aqueous solution by crosslinked chitosan beads: sorption kinetics and uptake mechanism

The crosslinked chitosan beads were used as an efficient biosorbent to remove perfluorooctane sulfonate (PFOS) from aqueous solution. The chitosan biosorbent had a sorption capacity up to 5.5 mmol/g for PFOS at the equilibrium concentration of 0.33 mmol/L, much higher than some conventional adsorbents. The sorption kinetics indicated that the sorption equilibrium was reached quickly at high pH and low PFOS concentrations, and the adsorbent size also affected the sorption rate to some extent. The double-exponential model described the kinetic data well, and the sorption of PFOS on the chitosan beads was a diffusion-controlled process. Based on the sorption kinetics and adsorbent characterization, the uptake mechanisms including electrostatic and hydrophobic interactions were identified to be responsible for PFOS sorption, and the hemi-micelles and micelles may form in the porous structure due to high PFOS concentrations within the adsorbent, which had the main contribution to the high sorption capacity.     

Evaluation and elimination of inhibitory effects of salts and heavy metal ions on biodegradation of Congo red by Pseudomonas sp. mutant

In this study, it was attempted to evaluate the influences and also recommended some elimination methods for inhibitory effects offered by salts and heavy metal ions. Congo red dye solution treated with mutant Pseudomonas sp. was taken as a model system for study. The salts used in this study are NaCl, CaCl₂ and MgSO₄·7H₂O. Though the growth was inhibited at concentrations above 4 g/l, toleration was achieved by acclimatization process. In case of heavy metal ions, Cr (VI) showed low inhibition up to 500 mg/l of concentration, compared to Zn (II) and Cu (II). It was due to the presence of chromium reductase enzyme which was confirmed by SDS-PAGE. Zn (II) and Cu (II) ion inhibitions were eliminated by chelation with EDTA. The critical ion concentrations obtained as per Han-Levenspiel model for Cr (VI), Zn (II) and Cu (II) were 0.8958, 0.3028 and 0.204 g/l respectively.     

Comparative studies on the adsorption of Cr(VI) ions on to various sorbents

The adsorption of Cr(VI) ions onto various sorbents (chitin, chitosan, ion exchangers; Purolite CT-275 (Purolite I), Purolite MN-500 (Purolite II) and Amberlite XAD-7) was investigated. Batch adsorption experiments were carried out as a function of pH, agitation period and concentration of Cr(VI) ions. The optimum pH for Cr(VI) adsorption was found as 3.0 for chitin and chitosan. The Cr(VI) uptake by ion exchangers was not very sensitive to changes in the pH of the adsorption medium. The maximum chromium sorption occurred at approximately 50 min for chitin, 40 min for Purolite II and 30 min for chitosan, Purolite I and Amberlite XAD-7. The suitability of the Freundlich and Langmuir adsorption models were also investigated for each chromium-sorbent system. Adsorption isothermal data could be accurately interpreted by the Langmuir equation for chitosan, chitin, Purolite I and Purolite II and by the Freundlich equation for chitosan, chitin and Amberlite XAD-7. The chromium(VI) ions could be removed from the sorbents rapidly by treatment with an aqueous EDTA solution and at the same time the sorbent regenerated and also could be used again to adsorb by heavy metal ions. The results showed that, chitosan, which is a readily available, economic sorbent, was found suitable for removing chromium from aqueous solution.     

The use of a white rot fungi (Pleurotus ostreatus) immobilized on Amberlite XAD-4 as a new biosorbent in trace metal determination

The present work proposes the use of Pleurotus ostreatus immobilized on Amberlite XAD-4 as new biosorbent in trace metal determination. The effects of experimental parameters, such as “pH and flow rate of sample solution, amount of solid phase, eluent type, and concentration” on the recovery of the metal ions were investigated. Maximum adsorption of Cr(III), Cd(II) and Cu(II) ions took place in the pH range 4-5. These metal ions can be desorbed with 1 M HCl (recovery 95-100%). 0.2 g adsorbent amount and 2.5 mL min⁻¹ flow rate was found to be optimum of all preconcentration experiments. The sorption capacity after 10 cycles of sorption and desorption does not vary more than 2.0%. The influences of the contaminant ions on the retentions of the analytes were also examined. The results showed that P. ostreatus immobilized on Amberlite XAD-4 can be considered as very promising material in trace metal determination.     

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.     

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).     

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.     

Probing copper/tau protein interactions electrochemically

Alzheimer’s disease (AD) is a neurodegenerative disorder that is characterized by peptide and protein misfolding and aggregation, in part due to the presence of excess metal ions such as copper(II) [Cu(II)]. Recently, the brain levels of Cu(II) complexes in vivo were linked to the oxidative stress in neurodegenerative disorders, including AD. Amyloid β-peptide (Aβ), found outside neuronal cells, has been investigated extensively in connection with Cu(II) ion toxicity; however, the effects of metallation on tau are less known. Normal tau protein binds and stabilizes the microtubules in neurons, but in diseased cells tau hyperphosphorylation and aggregation are evident and compromise tau function. There is increasing evidence that the Cu(II) ion may play an important role in tau biochemistry. Here, we present an electrochemical study of the interactions between full-length tau-410 and Cu(II) ions. The coordination of Cu(II) ions to tau immobilized on gold surfaces induces an electrochemical signal at approximately 140 ± 5 mV versus Ag/AgCl due to the Cu(II)/Cu(I) redox couple. Redox potentials and current intensities of Cu(II)-containing nonphosphorylated tau (nTau) and phosphorylated tau (pTau) films were determined at different pH conditions. Greater Cu(II) uptake by pTau over nTau films was observed at low pH. Competitive zinc(II) [Zn(II)] ion binding studies revealed significant Cu(II) ion displacement in pTau films. X-ray photoelectron spectroscopy analysis indicated the presence of Cu 2p and Zn 2p binding energies in protein samples, further supporting metal ion coordination to protein films. The surface-based electrochemical technique requires a minimal protein amount (a few microliters) and allows monitoring the bound Cu(II) ions and the redox activities of the resulting metalloprotein films.     

A new chitosan biopolymer derivative as metal-complexing agent: synthesis, characterization, and metal(II) ion adsorption studies

In this study, a new chitosan biopolymer derivative (CTSL) has been synthesized by anchoring a new vanillin-based complexing agent or ligand, namely 4-hydroxy-3-methoxy-5-[(4-methylpiperazin-1-yl)methyl] benzaldehyde, (L) with chitosan (CTS) by means of condensation. The new material was characterized by elemental (CHN), spectral (FTIR and solid state ¹³C NMR), thermal (TG-DTA and DSC), structural (powder XRD), and morphological (SEM) analyses. The CTSL was employed to study the equilibrium adsorption of various metal ions, namely, Mn(II), Fe(II), Co(II), Cu(II), Ni(II), Cd(II), and Pb(II), as functions of pH of the solutions. Its kinetics of adsorption was evaluated utilizing the pseudo first order and pseudo second order equation models and the equilibrium data were analyzed by Langmuir isotherm model. The CTSL shows good adsorption capacity for metal ions studied in the order Cu(II) > Ni(II) > Cd(II) ? Co ? Mn(II) > Fe(II) > Pb(II) in all studied pH ranges due to the presence of many coordinating moieties present in it.     

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.     

Mono-component versus binary isotherm models for Cu(II) and Pb(II) sorption from binary metal solution by the green alga Pithophora oedogonia

The sorption of Cu(II) and Pb(II) by Pithophora markedly decreased as the concentration of the secondary metal ion, Cu(II) or Pb(II), increased in the binary metal solution. However, the test alga showed a greater affinity to sorb Cu(II) than Pb(II) from the binary metal solution. Mono-component Freundlich, Langmuir, Redlich-Peterson and Sips isotherms successfully predicted the sorption of Cu(II) and Pb(II) from both single and binary metal solutions. None of the tested binary sorption isotherms could realistically predict Cu(II) and Pb(II) sorption capacity and affinity of the test alga for the binary metal solutions of varying composition, which mono-component isotherms could very well accomplish. Hence, mono-component isotherm modeling at different concentrations of the secondary metal ion seems to be a better option than binary isotherms for metal sorption from binary metal solution.     

Role of the Ca-pectates on the accumulation of heavy metals in the root apoplasm

In order to better understand the processes that regulate the accumulation in the apoplasm of heavy metals and their mobilization by the plant metabolites it is essential to study the mechanisms that regulate the interactions between metal ions and pectins. In such a context, the sorption of Cd(II), Zn(II), Cu(II) and Pb(II) from single and multi-metal solutions, by a Ca-polygalacturonate gel with a degree of esterification of 18.0 (PGAM₁) and 65.5% (PGAM₂) was studied in the 3.0–6.0 pH range in the presence of CaCl₂ 2.5 mM. The sorption of Cr(III) from single metal solution was also considered. The results show that the amount of each metal ion sorbed increases with increasing the initial metal ion concentration and pH. The data from the single metal solution tests show that at pH 6.0 the affinity of the metal ions towards the PGAM₁ matrix follows the order: Cr(III) > Cu(II) ? Pb(II) ? Zn(II) ? Cd(II). The simultaneous sorption of the bivalent metal ions by the PGAM₁ gels indicates that Pb(II) is selectively sorbed. The FT-IR spectra show that the carboxylate groups are mainly responsible for the metal ion coordination. The ability of PGAM₂ to accumulate Cr(III), Cu(II), and Pb(II) was lower than that found in the PGAM₁ systems whereas the sorption of Zn(II) and Cd(II) was negligible.     

Removal of copper(II) using chitin/chitosan nano-hydroxyapatite composite

Polymeric composites made up of nano-hydroxyapatite (n-HAp) with chitin and chitosan have been prepared and studied for the removal of Cu(II) ions from the aqueous solution. The sorption capacity (SC) of n-HAp, n-HAp/chitin (n-HApC) composite and n-HAp/chitosan (n-HApCs) composite were found to be 4.7, 5.4 and 6.2 mg/g respectively with a minimum contact time of 30 min. Batch adsorption studies were conducted to optimize various equilibrating conditions like contact time, pH and selectivity of metal ion. The sorbents were characterized by FTIR, TEM, XRD and SEM with EDAX analysis. The sorption process was explained with Freundlich and Langmuir isotherms respectively. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated to understand the nature of sorption. A suitable mechanism for copper sorption was established and the selectivity of the metal ions for the composites was identified.