Chemical Modification ofSargassum sp. for Prevention of Organic Leaching and Enhancement of Uptake during Metal Biosorption

Gold biosorption by exopolysaccharide producing cyanobacteria and purple nonsulphur bacteria

AIMS

This study was aimed at investigating the possible exploitation of phototrophic micro-organisms for the removal and the recovery of Au from Au-containing wastewaters deriving from a plating industry.

METHODS AND RESULTS

A screening among ten phototrophic micro-organisms was carried out with pure solutions of Au to select the best strain in terms of metal uptake and selectivity. The direct use of the selected micro-organism on the Au-containing industrial wastewater was then carried out with the aim of assessing the potential of its use for the removal and the recovery of the precious metal from industrial wastewaters.

CONCLUSIONS

This study showed the good potential of some exopolysaccharide-producing cyanobacteria as biosorbents for the recovery of Au from wastewaters of plating industries but also pointed out the need to design an efficient technology for the recovery of the metal from the biomass.

SIGNIFICANCE AND IMPACT OF THE STUDY

The selection of good biosorbents for the recovery of gold from industrial wastewaters may open new perspectives to a green biotechnology so far considered too expensive for the mere treatment of wastewaters containing low valuable metals.

Cd(II) biosorption using Lessonia kelps

Lessonia kelps (L. trabeculata and L. nigrescens) have been successfully used for the recovery of Cd(II) from near neutral solutions. The biomass was pre-treated with calcium chloride for stabilization of alginate-based compounds. SEM-EDAX analysis and FT-IR spectrometry analysis were used for identifying the modifications of the biomass. Sorption isotherms were performed at the optimum pH (i.e., pH 6) and the maximum sorption capacity reached up to 1 and 1.5 mmol Cd g(-1) for L. nigrescens (L.n.) and L. trabeculata (L.t.), respectively. The Langmuir equation fits well experimental data. The temperature (in the range 20-40 °C) had a more marked effect on affinity coefficient than on maximum sorption capacity. The influence of particle size, sorbent dosage, metal concentration and temperature was evaluated on uptake kinetics. The kinetic profiles that were modeled using the Crank equation (i.e., the resistance to intraparticle diffusion) were hardly affected by the temperature and the particle size contrary to the sorbent dosage and the metal concentration, which show greater impact. The pseudo-second order rate equation was also tested for the modeling of uptake kinetics.

Characterization of hexavalent chromium interaction with Sargassum by X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry calculation

Hexavalent chromium represents higher toxicity in aqueous solutions. It can be removed by such low-cost biosorbents as Sargassum sp. In this study, X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry (QC) calculation were used to study the interactions between hexavalent chromium and Sargassum sp. during the biosorption. It was found that most of the adsorbed Cr(VI) ions were reduced to Cr(III) after the biosorption. The electrons for the reduction of Cr(VI) were possibly supplied from the Sargassum biomass, some organic compounds of which were oxidized. Cr(III) ions were coordinated with the oxygen atoms from either carboxyl or hydroxyl functional groups to form an octahedral structural metal complex. The coordination numbers of the formed Cr complex were 4-6, and bond length of Cr-O was 1.98Å. QC calculation proved the possible formation of the Cr(III) metal complex, and revealed that carboxyl from biomass could be strongly bound with Cr(III). A three-step removal mechanism of Cr(VI) by Sargassum was proposed.

Preparation and characterization of chitosan encapsulated Sargassum sp. biosorbent for nickel ions sorption

A new biosorbent -Sargassum sp. encapsulated with epichlorohydrin (ECH) cross-linked chitosan (CS) was investigated for nickel ions removal. The prepared biosorbent with Sargassum sp. to cross-linked chitosan of 3 (weight ratio) had the highest sorption capacity. The biosorption kinetics can be well fitted by the diffusion-controlled model. The organic leaching of CS was 77-88% less than that of algae at different pH. The biosorption capacity of nickel on CS was much higher than that of cross-linked chitosan (CLC) bead and lower than that of raw algae due to encapsulation. In addition, the reusability of CS was further evaluated and confirmed through five adsorption-desorption cycles. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the nickel ions sequestration mechanism included ion exchange and nickel complexation with the carboxyl, amino, alcoholic and ether groups in CS.

Improvement of metal adsorption onto chitosan/Sargassum sp. composite sorbent by an innovative ion-imprint technology

Technology for immobilization of biomass has attracted a great interest due to the high sorption capacity of biomass for sequestration of toxic metals from industrial effluents. However, the currently practiced immobilization methods normally reduce the metal sorption capacities. In this study, an innovative ion-imprint technology was developed to overcome the drawback. Copper ion was first imprinted onto the functional groups of chitosan that formed a pellet-typed sorbent through the granulation with Sargassum sp.; the imprinted copper ion was chemically detached from the sorbent, leading to the formation of a novel copper ion-imprinted chitosan/Sargassum sp. (CICS) composite adsorbent. The copper sorption on CICS was found to be highly pH-dependent and the maximum uptake capacity was achieved at pH 4.7-5.5. The adsorption isotherm study showed the maximum sorption capacity of CICS of 1.08 mmol/g, much higher than the non-imprinted chitosan/Sargassum sp. sorbent (NICS) (0.49 mmol/g). The used sorbent was reusable after being regenerated through desorption. The FTIR and XPS studies revealed that the greater sorption of heavy metal was attributed to the large number of primary amine groups available on the surfaces of the ion-imprinted chitosan and the abundant carboxyl groups on Sargassum sp. Finally, an intraparticle surface diffusion controlled model well described the sorption history of the sorbents.

Studies on sorption, desorption, regeneration and reuse of sugar-beet pectin gels for heavy metal removal

This work reports the effectiveness of sugar-beet pectin xerogels for the removal of heavy metals (cadmium, lead and copper) after multiple batch sorption-desorption cycles, with and without a gels regeneration step. Metals were recovered from xerogel beads without destroying their sorption capability and the beads were successfully reused (nine cycles) without significant loss in both biosorption capacity and biosorbent mass. Metals uptake levelled off or increased after using a 1M CaCl(2) regeneration step after each desorption. Calcium, as a regenerating agent, increased the stability and reusability of the gels repairing the damage caused by the acid and removing the excess protons after each elution providing new binding sites. Because of their excellent reusability, pectin xerogels are suitable for metal remediation technologies.

Lead(II) adsorption from aqueous solutions by raw and activated charcoals of Melocanna baccifera Roxburgh (bamboo)--a comparative study

Melocanna baccifera (Poaceae) is the most abundant and economically important non-timber product in state of Mizoram, India. The communities of the region use this potential resource in many ways, charcoal production is one of them. Bamboo charcoal has application in food, pharmaceutical and chemical industries. Activated charcoal was prepared from M. baccifera charcoal by chemical pretreatment in order to make better use of this abundant biomass material. Batch experiments were conducted under varying range of pH (2.0-6.0), contact time (15-360 min) and metal ion concentrations (50-90 mg L(-1)). The optimum conditions for lead biosorption are almost same for M. baccifera raw charcoal (MBRC) and M. baccifera activated charcoal (MBAC)-pH 5.0, contact time 120 min, adsorption capacity q(max) 10.66 mg g(-1) and 53.76 mg g(-1), respectively. However, the biomass of MBAC was found to be more suitable than MBRC for the development of an efficient adsorbent for the removal of lead(II) from aqueous solutions. FTIR analysis revealed that -OH, C-H bending, C=O stretching vibration and carbonyl functional groups were mainly responsible for Pb(II) biosorption. Thus, this study demonstrated that both the charcoal biomass could be used as adsorbents for the treatment of Pb(II) from aqueous solution.

A novel two-resistance model for description of the adsorption kinetics onto porous particles

A novel two-resistance model for description of the sorption kinetics by porous particles has been proposed. The model takes into account two kinetic steps of different kinds which are involved in the overall sorption process rate: (i) the rate of solute diffusion in pores of the sorbent particles having uniform sizes and characterized by the homogeneous intraparticle diffusion coefficient and (ii) the rate of a direct adsorption/desorption process on the surface, described by applying the statistical rate theory (SRT) approach. Two different kinds of sorbent particles geometry are considered: the spherical and the plane particles, having their dimension characterized by radius and thickness, respectively. The meaning of the parameters which influence the sorption kinetics has been discussed. The results make it possible to judge which conditions have to be fulfilled to consider only one kinetic step and, thus, to simplify the theoretical description of a given system. The conclusion has been drawn that the concave character of kinetic sorption isotherms plotted in the function of the square root of time is of a general nature and is connected with the situation when at least two different processes are involved in controlling the sorption kinetics.

A comparative study of natural, formaldehyde-treated and copolymer-grafted orange peel for Pb(II) adsorption under batch and continuous mode

Natural, formaldehyde-treated and copolymer-grafted orange peels were evaluated as adsorbents to remove lead ions from aqueous solutions. The optimum pH for lead adsorption was found to be pH 5. The adsorption process was fast, reaching 99% of sorbent capacity in 10 min for the natural and treated biomasses and 20 min for the grafted material. The treated biomass showed the highest sorption rate and capacity in the batch experiments, with the results fitting well to a pseudo-first order rate equation. In the continuous test with the treated biomass, the capacity at complete exhaustion was 46.61 mg g(-1) for an initial concentration of 150 mg L(-1). Scanning electronic microscopy and energy dispersive X-ray spectroscopy indicated that the materials had a rough surface, and that the adsorption of the metal took place on the surface. Fourier transform infrared spectroscopy revealed that the functional groups responsible for metallic biosorption were the -OH, -COOH and -NH(2) groups on the surface. Finally, the thermogravimetric analysis indicates that a mass reduction of 80% can be achieved at 600 degrees C.

Evaluation of untreated coffee husks as potential biosorbents for treatment of dye contaminated waters

The objective of this work was to propose an alternative use for coffee husks (CH), a coffee processing residue, as untreated sorbents for the removal of methylene blue (MB) from aqueous solutions. The effects of solution temperature, pH, biosorbent dosage and contact time on MB removal were investigated. The experimental adsorption equilibrium data were fitted to both Langmuir and Freundlich adsorption models. The biosorption kinetics was determined by fitting first and second-order kinetic models to the experimental data, with the second-order model providing the best description of MB adsorption onto coffee husks. pH variations did not present a significant effect on MB removal. Evaluation of thermodynamics parameters indicated that the adsorption is spontaneous and endothermic. The experimental data obtained in the present study demonstrated coffee husks to be suitable candidates for use as biosorbents in the removal of cationic dyes.

Enhanced and selective adsorption of Pb2+ and Cu2+ by EDTAD-modified biomass of baker's yeast

Enhanced and selective removal of Pb2+ and Cu2+ in the presence of high concentration of K+, Na+, Ca2+ and Mg2+ were achieved by adsorption on biomass of baker's yeast modified with ethylenediaminetetraacetic dianhydride (EDTAD). The modified biomass was found to have high adsorption capacities and fast rates for Pb2+ and Cu2+, and it also displayed consistently high levels of metal uptake over the pH range from 2.7 to 6.0. From Langmuir isotherm, the adsorption capacities for Pb2+ and Cu2+ were found to be 192.3 and 65.0 mg g(-1), respectively, which are about 10 and 14 times higher than that of the unmodified biomass. Competitive biosorption experiments showed that the co-ions of K+, Na+, Ca2+ and Mg2+ had little effects on the uptake of Pb2+ and Cu2+ even at the concentration of 1.0 mol L(-1). The adsorbed Pb2+ and Cu2+ on the modified biomass could be effectively desorbed in an EDTA solution, and the regenerated biomass could be reused repeatedly with little loss of the adsorption capacity.

Untreated coffee husks as biosorbents for the removal of heavy metals from aqueous solutions

The objective of this work was to propose an alternative use for coffee husks (CH), a coffee processing residue, as untreated sorbents for the removal of heavy metal ions from aqueous solutions. Biosorption studies were conducted in a batch system as a function of contact time, initial metal ion concentration, biosorbent concentration and pH of the solution. A contact time of 72 h assured attainment of equilibrium for Cu(II), Cd(II) and Zn(II). The sorption efficiency after equilibrium was higher for Cu(II) (89-98% adsorption), followed by Cd(II) (65-85%) and Zn(II) (48-79%). Even though equilibrium was not attained in the case of Cr(VI) ions, sorption efficiency ranged from 79 to 86%. Sorption performance improved as metal ions concentrations were lowered. The experimental sorption equilibrium data were fitted by both Langmuir and Freundlich sorption models, with Langmuir providing the best fit (R2>0.95). The biosorption kinetics was determined by fitting first and second-order kinetic models to the experimental data, being better described by the pseudo-second-order model (R2>0.99). The amount of metal ions sorbed increased with the biosorbent concentration in the case of Cu(II) and Cr(VI) and did not present significant variations for the other metal ions. The effect of the initial pH in the biosorption efficiency was verified in the pH range of 4-7, and the results showed that the highest adsorption capacity occurred at distinct pH values for each metal ion. A comparison of the maximum sorption capacity of several untreated biomaterial-based residues showed that coffee husks are suitable candidates for use as biosorbents in the removal of heavy metals from aqueous solutions.

Biosorption of copper(II) by Marrubium globosum subsp. globosum leaves powder: effect of chemical pretreatment

The study was aimed at determining the effect of chemical pretreatment on copper(II) biosorption by Marrubium globosum subsp. globosum leaves. The uptake capacity of the biomass was increased by chemical pretreatment when compared with the raw biomass. The results of biosorption experiments, carried out at the conditions of 50 mg l(-1) initial metal concentration and pH 5.5, showed that pretreating the biomass with alkali solutions (laundry detergent, sodium hydroxide and sodium bicarbonate, 0.5 M) improved the biosorption capacity of biomass (45.90, 45.78 and 43.91%, respectively) compared with raw biomass. Pretreatment with sulfuric and nitric acid solutions, 0.5 M, increased the biosorption capacity of biomass by 11.82 and 10.18%, respectively, while there was no considerable change in the biosorption capacity of biomass (0.35%) after pretreatment with formic acid solution, 0.5 M. Furthermore, sodium chloride and calcium chloride, 0.5 M, pretreatments resulted in the improvement in biosorption capacity of biomass (31.38 and 26.69%, respectively). FT-IR analysis revealed that hydroxyl and carboxyl functional groups were mainly responsible for copper(II) biosorption.

Biosorption of hexavalent chromium onto raw and chemically modified Sargassum sp

Hexavalent chromium biosorption by raw algae is always accompanied with significantly high organic leaching. In this study, hydrochloric acid, sodium hydroxide, calcium chloride, formaldehyde, and glutaraldehyde were used for modification of raw Sargassum sp. seaweed (RSW), in order that the modified seaweed (MSW) has a lower organic leaching while the metal biosorption capacity is comparable to the RSW. The result shows that the chemical modification by 0.2% formaldehyde achieves such goals. The biosorption of both RSW and MSW is highly pH dependent. At the optimal pH of 2.0, the maximum biosorption capacities of MSW and RSW are 1.123 and 0.601 mmol g(-1), respectively. The surface treatment improves the reduction capacity of the biosorbents. The instrumental analysis demonstrates that the Cr(VI) biosorption is controlled by redox, ion exchange and coordination reactions, of which alcohol, carboxyl, amino and sulphonic groups play important roles. The complete uptake of hexavalent chromium is achieved in 20 h. The chemical reduction for Cr(VI) to Cr(III) is pH dependent and controls the overall chromium removal kinetics.

A combined electrocoagulation-sorption process applied to mixed industrial wastewater

The removal of organic pollutants from a highly complex industrial wastewater by a aluminium electrocoagulation process coupled with biosorption was evaluated. Under optimal conditions of pH 8 and 45.45 Am(-2) current density, the electrochemical method yields a very effective reduction of all organic pollutants, this reduction was enhanced when the biosorption treatment was applied as a polishing step. Treatment reduced chemical oxygen demand (COD) by 84%, biochemical oxygen demand (BOD(5)) by 78%, color by 97%, turbidity by 98% and fecal coliforms by 99%. The chemical species formed in aqueous solution were determined. The initial and final pollutant levels in the wastewater were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and elemental composition of the biosorbent was characterized with scanning electron microscopy (SEM) and energy dispersion spectra (EDS).

Cystine-modified biomass for Cd(II) and Pb(II) biosorption

The surface of dried biomass of baker's yeast was modified by crosslinking cystine with glutaraldehyde. X-ray photoelectron spectroscopy and microscope were used to characterize the modified biomass. The adsorption capacity of the modified biomass for Cd(2+) and Pb(2+) showed an increase compared with the pristine biomass due to the presence of cystine on the biomass surface. Experimental data showed that the adsorption of the two metal ions increased with time until equilibrium was achieved. The adsorption capacities for Cd(2+) and Pb(2+) were 11.63 and 45.87 mg g(-1), respectively, which were determined from the Langmuir isotherm. The loaded biosorbent was regenerated using HCl solution and could be used repeatedly at six times with little loss of uptake capacity. FTIR spectroscopy revealed that carboxyl, amide, and hydroxyl groups on the biomass surface were involved in the adsorption of Cd(2+) and Pb(2+).

Batch desorption studies and multiple sorption-regeneration cycles in a fixed-bed column for Cd(II) elimination by protonated Sargassum muticum

The protonated alga Sargassum muticum was employed in batch desorption studies to find the most appropriate eluting agent for Cd(II)-laden biomass regeneration. Eleven types of eluting solutions at different concentrations were tested, finding elution efficiencies higher than 90% for most of the desorbents studied. Total organic carbon and biomass weight loss measurements were made. The reusability of the protonated alga was also studied using a fixed-bed column. Eleven consecutive sorption-regeneration cycles at a flow rate of 10 mL min(-1) were carried out for the removal of 50 mg L(-1) Cd(II) solution. A 0.1M HNO(3) solution was employed as desorbing agent. The column was operated during 605 h for sorption and 66 h for desorption, equivalent to a continuous use during 28 days, with no apparent loss of sorption performance. In these cycles, no diminution of the breakthrough time was found; although, a relative loss of sorption capacity, regarding the found in the first cycle, was observed. The slope of the breakthrough curves experiments a gradual increase reaching its maximum value for the last cycle tested (40% greater than for the first one). The maximum Cd(II) concentration elution peak was achieved in 5 min or less, and the metal effluent concentration was always lower than 0.9 mg L(-1) after 1 h of elution. The maximum concentration factor was determined to be between 55 and 109.

Surface complexation mechanism and modeling in Cr(III) biosorption by a microalgal isolate, Chlorella miniata

The mechanism involved in the removal of Cr(III) by a green microalgal isolate, Chlorella miniata, was examined based on a series of batch experiments and microscopic analyses, and a mathematical model was proposed. Results showed that Cr(III) biosorption increased with the increase of pH from 2.0 to 4.5, and no significant changes in biosorption outside this pH range. Langmuir isotherm indicated that the maximum Cr(III) sorption capacity of Chlorella miniata was 14.17, 28.72, and 41.12 mg g(-1) biomass at pH 3.0, 4.0, and 4.5, respectively. Results from desorption studies, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and EDX (energy-dispersive X-ray spectroscope) analyses confirmed that surface complexation was the main process involved in Cr(III) biosorption. Potentiometric titration revealed that carboxyl (pKa1 = 4.10), phosphonate (pKa2 = 6.36) and amine (pKa3 = 8.47) functional groups on the surface of Chlorella miniata were the possible sites for Cr uptake, and their average amounts were 0.53, 0.39, and 0.36 mmol g(-1) biomass, respectively. A surface complexation model further indicated that carboxyl group played the main role in Cr(III) complexation, with a binding constant of K11 = 1.87 x 10(-4) and K12 = 6.11 x 10(-4) for Cr3+ and Cr(OH)2+, respectively. This model also suggested that the hydroxy species was more easily to complex with the cell surface of Chlorella miniata.