Column biosorption of lanthanum and europium by Sargassum.

Batch and column biosorption of La(3+) (lanthanum) and Eu(3+) (europium) was studied using protonated Sargassum polycystum biomass. The ion exchange sorption mechanism was confirmed by the proportional release of protons and by the total normality of the solution, which remained constant during the process. Equilibrium isotherms were determined for the binary systems, La/H and Eu/H for a total normality of 3 meq g(-1), which produced separation factors of 2.7 and 4.7, respectively, demonstrating a higher affinity of the biomass towards europium. Column runs with a single metal feed were used to estimate the intra-particle mass transfer coefficients for La and Eu (6.0 x 10(-4) and 3.7 x 10(-4) min(-1), respectively). Modeling batch and column binary systems with proton as the common ion was able to predict reasonably well the behavior of a ternary system containing protons. The software FEMLAB was used for solving the set of coupled partial differential equations. Moreover, a series of consecutive sorption/desorption runs demonstrated that the metal could be recovered and the biomass reused in multiple cycles by using 0.1N HCl with no apparent loss in the biosorbent metal uptake capacity.

Biosorption and me.

Biosorption has been defined as the property of certain biomolecules (or types of biomass) to bind and concentrate selected ions or other molecules from aqueous solutions. As opposed to a much more complex phenomenon of bioaccumulation based on active metabolic transport, biosorption by dead biomass (or by some molecules and/or their active groups) is passive and based mainly on the "affinity" between the (bio-)sorbent and sorbate. A personal overview of the field and its origins is given here, focusing on R&D reasoning and know-how that is not normally published in the scientific literature. While biosorption of heavy metals has become a popular environmentally driven research topic, it represents only one particular type of a concentration-removal aspect of the sorption process. The methodology of studying biosorption is based on an interdisciplinary approach to it, whereby the phenomenon can be studied, examined and analyzed from different angles and perspectives-by chemists, (micro-)biologists as well as (process) engineers. A pragmatic science approach directs us towards the ultimate application of the phenomenon when reasonably well understood. Considering the variety of parameters affecting the biosorption performance, we have to avoid the endless empirical and, indeed, alchemistic approach to elucidating and optimizing the phenomenon-and this is where the power of computers becomes most useful. This is all still in the domain of science-or "directed curiosity". When the knowledge of biosorption is adequate, it is time to use it-applications of certain types of biosorption are on the horizon, inviting the "new technology" enterprise ventures and presenting new and quite different challenges.

Biosorption of arsenic (V) with acid-washed crab shells.

Highly toxic arsenate occurs naturally in some well water as well as in industrial wastewaters. Removal of arsenate (As(V)) by biosorption with acid-washed crab shells (AWCS) is very sensitive to solution pH. It greatly increased when the solution pH was lowered from 3.44+/-0.07 to 2.51+/-0.02, but it was reduced at pH below 1.99+/-0.01. Change of solution pH not only affected the charged functional groups on AWCS but also the speciation of arsenate in solution. Increasing ionic strength of solution negatively affected the arsenic uptake. At ionic strength 0.1M, arsenic uptake was seriously depressed. Arsenic biosorption with AWCS was mainly through arsenate binding on the amide groups in the AWCS. AWCS has a dense structure and low extent of swelling in aqueous solutions. This might prevent effective arsenate access to the functional groups in AWCS.

Stabilization of the initial electrochemical potential for a metal-based potentiometric titration study of a biosorption process.

An interactive metal-based potentiometric titration method has been developed using an ion selective electrode for studying the sorption of metal cations. The accuracy of this technique was verified by analyzing the metal sorption mechanism for the biomass of Rhizopus arrhizus fungus and diatomite, two dissimilar materials (organic and mineral, strong sorbent and weak sorbent) of a different order of cation exchange capacity. The problem of the initial electrochemical potential was addressed identifying the usefulness of a Na-sulfonic resin as a strong chelating agent applied before the beginning of sorption titration experiments so that the titration curves and the sorption uptake could be quantitatively compared. The resin stabilized the initial electrochemical potential to -405+/-5 mV corresponding to 2 micro gl(-1) of lead concentration in solution. The amounts of lead sorbed by R. arrhizus biomass and diatomite were 0.9 mmol g(-1) (C(e)=5.16 x 10(-2)mM) and 0.052 mmol g(-1) (C(e)=5.97 x 10(-2) mM), respectively. Lead sorption by the fungal biomass was pinpointed to at least two types of chemical active sites. The first type was distinguished by high reactivity and a low number of sites whereas the other was characterized by their higher number and lower reactivity.

Biosorption of La, Eu and Yb using Sargassum biomass.

Biosorption of the lanthanides: Lanthanum (La(3+)), Europium (Eu(3+)) and Ytterbium (Yb(3+)) from single-component and multi-component batch systems using Sargassum polycystum Ca-loaded biomass was studied. The ion exchange sorption mechanism was confirmed by the release of calcium ions from the biomass that matched the total number of metal and protons removed from the solution. The metal binding increased with pH due to the decrease of proton concentration in the system, as they also compete for the binding sites. The maximum metal uptake capacity for pH 3, 4 and 5 ranged approximately between (0.8-0.9) mmol g(-1) for La (0.8-0.9) mmol g(-1) for Eu, and (0.7-0.9) mmol g(-1) for Yb. Biosorption from multi-component mixtures was examined at pH 4 using equimolar initial concentrations of the metals. The metal affinity sequence established was Eu>La>Yb, and the maximum metal uptake obtained was 0.29, 0.41, 0.28 mmol g(-1) for La, Eu and Yb, respectively.

Effect of counterions on lanthanum biosorption by Sargassum polycystum.

The effect of the presence of different anions on the biosorption of La(3+) (Lanthanum) using Sargassum polycystum Ca-loaded biomass was studied in this work. Different types of metal salts were used, such as nitrate, sulphate and chloride. The presence of the anion sulphate decreased the metal uptake for tested pH values of 3--5 when compared to the nitrate and chloride systems. The presence of chloride ions did not seem to interfere with the lanthanum removal. The speciation of lanthanum in solution could explain the differences obtained for the different systems and the Mineql+ program was used for the calculations. A monovalent complex with sulphate and lanthanum was formed that had lower apparent affinity towards the biomass compared to the free trivalent metal ion. The La uptake varied from 0.6 to 1.0 mmol g(-1). The Langmuir model was used to describe quantitatively the sorption isotherms. The addition of sulphuric acid for pH adjustment decreased the metal uptake from lanthanum sulphate solutions when compared to the nitric acid addition. The effect was more pronounced with sulphuric acid due to the formation of complexes.

A high-resolution titrator: a new approach to studying binding sites of microbial biosorbents.

The high-resolution potentiometric titration was used as a physico-chemical method to study the acid properties of selected biosorbent materials in order to quantify the functional acidic groups for sorption and to determine their affinities by considering their partial or total ionization equilibrium reactions. The Gran's method and the Henderson-Hasselbach's equation were employed in establishing the partition of the total acidity as associated with strong, weak and very weak acidic chemical active groups. The differences in the total organic acidity (A(TO)) for the two selected types of bacteria and two mycelia revealed by this method were explained by the chemical composition of their cell walls. The total organic acidities obtained were 3.87 me g(-1) for Thiobacillus ferrooxidans, 1.31 me g(-1) for Corynebacterium glutamicum, 0.81 me g(-1) for Aspergillus niger and 2.54 me g(-1) for Rhizopus arrhizus. The links between the activity of protons and the sorption capacities of the selected bioorganic matters were established. Sorption of lead by C. glutamicum and R. arrhizus biomass indicated an optimum pH of 6. It appeared that 64% (Pb(uptake)=0.48 me g(-1)) and 38% (Pb(uptake)=0.28 me g(-1)) of A(TO) were involved during lead sorption onto R. arrhizus and C. glutamicum, respectively. The applications of titration techniques become a powerful tool for the characterization of heterogeneous materials involved in biosorption and bioremediation processes.

Lead biosorption study with Rhizopus arrhizus using a metal-based titration technique.

Acid-base and metal-based potentiometric titration methods were used to analyze sorption mechanisms of lead by Rhizopus arrhizus fungal biomass. Biosorption was not considered globally but as the result of successive sorption reactions on various binding sites with different selectivities. Precipitation occurred rapidly when lead concentration increased. Lead was sorbed essentially by carboxylic groups and by phosphates and sulfonates (less abundant) of the organic matter. The lead affinity to carboxylic, sulfonate and phosphate binding sites depended on the association coefficient with proton or counter-ion and on the spatial distribution of the surface sites promoting the formation of mono- or bi-dentate complexes. Chemical bonds and binding sites were confirmed using microscopic and spectroscopic techniques (IR, MET-EDAX). It appeared that although the total organic acidity was reached, number of ionized and free carboxylic groups were not involved in lead sorption reactions. In spite of lead speciation in the solution, surface micro-precipitation was observed and the two processes, surface adsorption and micro-precipitation, are sequential and possibly overlapping. At low concentrations (<10(-6) M) adsorption is the dominant phenomenon and beyond (>10(-5) M) surface clusters appeared before the predicted solution precipitation phenomenon.

A review of the biochemistry of heavy metal biosorption by brown algae.

The passive removal of toxic heavy metals such as Cd(2+), Cu(2+), Zn(2+), Pb(2+), Cr(3+), and Hg(2+) by inexpensive biomaterials, termed biosorption, requires that the substrate displays high metal uptake and selectivity, as well as suitable mechanical properties for applied remediation scenarios. In recent years, many low-cost sorbents have been investigated, but the brown algae have since proven to be the most effective and promising substrates. It is their basic biochemical constitution that is responsible for this enhanced performance among biomaterials. More specifically, it is the properties of cell wall constituents, such as alginate and fucoidan, which are chiefly responsible for heavy metal chelation. In this comprehensive review, the emphasis is on outlining the biochemical properties of the brown algae that set them apart from other algal biosorbents. A detailed description of the macromolecular conformation of the alginate biopolymer is offered in order to explain the heavy metal selectivity displayed by the brown algae. The role of cellular structure, storage polysaccharides, cell wall and extracellular polysaccharides is evaluated in terms of their potential for metal sequestration. Binding mechanisms are discussed, including the key functional groups involved and the ion-exchange process. Quantification of metal-biomass interactions is fundamental to the evaluation of potential implementation strategies, hence sorption isotherms, ion-exchange constants, as well as models used to characterize algal biosorption are reviewed. The sorption behavior (i.e., capacity, affinity) of brown algae with various heavy metals is summarized and their relative performance is evaluated.

1H-NMR study of Na alginates extracted from Sargassum spp. in relation to metal biosorption.

The use of a number of species of marine brown algae in the implementation of bioremediation strategies for toxic heavy metals is being considered and evaluated. The biosorption capacity of these algae for heavy metals resides mainly in a group of linear polysaccharides known as alginates that occur as a gel in the algal thallus. The potential for selective metal binding by the biomass of two species of Sargassum was evaluated by 1H-NMR (nuclear magnetic resonance) following a high temperature, alkaline extraction and purification of their alginate polysaccharide. The alkaline extraction protocol applied to Sargassum fluitans and Sargassum siliquosum yielded alginate samples of low viscosity, suitable for direct acquisition of well-resolved spectra. Estimates of both the ratio of beta-D-mannopyranuronosyl (M) and alpha-L-gulopyranuronosyl (G) residues along the polymer chain and the frequencies of occurrence of diad uronic acid residue pairs were obtained. Guluronic acid (G) was the major component in all extracts and the GG diads accounted for more than 49% of the polymer diads. Whereas the performance of Sargassum spp. in the metal biosorption process is a function of both its alginate content and composition, the occurrence of "G-blocks" in both purified alginates and in the raw brown seaweed is critical because it results in a well-established selectivity for divalent ions, potentially increasing the commercial effectiveness of targeted biosorption as a means of remediation.

Dynamic and equilibrium studies of the RDX removal from soil using CMC-coated zerovalent iron nanoparticles.

Rapid chemical degradation of toxic RDX explosive in soil can be accomplished using zerovalent nanoiron suspension stabilized in dilute carboxymethyl cellulose solution (CMC-ZVINs). The effect of operating conditions (redox-potential, Fe/RDX molar ratio) was studied on batchwise removal of RDX in contaminated soil. While anaerobic conditions resulted in 98% RDX removal in 3 h, only slightly over 60% RDX removal could be attained under aerobic conditions. The molar ratio did not have any influence on the intermediate and final RDX degradation products (methylenedinitramine, nitroso derivative, N(2), N(2)O, NO(2)(-)), however, their distribution changed. Dynamic studies were conducted using a flow-through short column packed with RDX-contaminated soil and fed with CMC-ZVINs. The column was operated at two interstitial velocities (2.2 and 1.6 cm min(-1)), resulting in the 76.6% and 95% removal of the initial RDX soil contamination load (60 mg kg(-1)), respectively. While the column operating conditions could be further optimized, 95% of the RDX initially present in the contaminated soil packed in the column was degraded when flushed with a CMC-ZVINs suspension in this work.

Optimization of a biosorption column performance.

The dynamics of copper and zinc biosorption by Sargassum fluitans was analyzed under variable column operating conditions including different column lengths (15 and 45 cm), metal-feed solution concentrations (1 and 6 meq L(-1)), metal-sorbent affinities (2.01 and 0.45), and interstitial velocities (12 and 4 cm min(-1)). The experimental breakthrough curves obtained under these varying conditions were also simulated using a mathematical model taking into account the mass transfer as well as the axial dispersion phenomena. The column performance was evaluated using two performance indicators: the service time (t(s)) and the unused portion of the column as reflected in the area under the breakthrough curve (A(c)). Sensitivity analysis results indicated that the feed stream concentration, mass transfer coefficient, column length, and interstitial velocity had the most important effect on the column performance. Applying chromatography theories, the optimization of the biosorption process for productivity and sorption performance, in terms of operating conditions (interstitial velocity) and design parameters (column length), was outlined. The corresponding optimum curve relating the interstitial velocity and the column length resulted with the pressure drop limitations recognized. As an example, a laboratory column 100 cm long will necessitate an interstitial velocity of 19 cm min(-1) to yield the best sorption results.

Behavior of the mass transfer zone in a biosorption column.

Modeling of the mass transfer zone behavior under variable conditions in a flow-through fixed-bed sorption column enabled the prediction of breakthrough curves for Cu2+ and Ca-preloaded Sargassum fluitans biomass. The mass transfer resistance, particle diffusion, and the axial dispersion were incorporated in the model. The dynamics of the mass transfer zone was described under variable sorption column operating conditions including different column lengths and fluid flow rates. Accurate estimation of the behavior of the mass transfer zone as it progressed through the column, reflected eventually in the breakthrough curve, assisted in its relevant interpretations. Furthermore, the proposed mathematical model of the biosorption process was capable of demonstrating the expanding and broadening of the mass transfer zone linked to the equilibrium sorption isotherm. The fundamental understanding of the mass transfer zone dynamics is particularly important for process scale-up where maintaining the process efficiency is critical.

Comparative testing of tangential microfiltration for microbial cultures.

In an attempt to extend and intensify the productive periods of bioprocesses, a self-cleaning tangential filtration device was examined. Built into a special-design bioreactor, its cell retention was evaluated for continuous-flow operation with selected examples of bacteria (Escherichia coli), yeasts (Sacharomyces cerevisiae), and filamentous fungi (Aspergillus niger). Performance characteristics such as filtration rates and cell accumulation were assessed as a function of filter rotational speed, operating pressure, cultivation time, and microfilter type (i.e., membrane or porous metallic). The highest flux of cell-free filtrate for each culture type was achieved using a 0.45-micron membrane-covered microfilter. While the respective yeast (S. cerevisiae) and bacterial (E. coli) cell concentrations were enhanced by as much as 16- and 8-fold over the batch growth levels, the representative A. niger fungal cultivation was less satisfactory because of progressively declining filtration rates limited by hydraulically resistant layers of microbial surface growth quite resistant to in situ filter backflushing with gas. Maximum steady-state flux was independent of operating pressure, yet was enhanced at rotational speeds up to about 800 rpm. Higher speeds offered no further improvements. The overall fermentation process was limited by the moderate levels of attainable flux which restricted the feed and dilution rates. The maximum attainable stabilized fluxes were 26-40 L/m(2) x h.

Modeling of lithium interference in cadmium biosorption.

Biosorption of Cd by the brown seaweed Sargassum polycystum biomass was experimentally investigated and mathematically modeled at different pH and ionic strength levels. From the potentiometric titration of the biomass, three types of functional groups were identified, and the dissociation constant and the numbers of these groups were determined. The carboxyl group (pK(H) 3.70 +/- 0.09) was found to play a major role in binding protons and Cd. The background ion, Li+, could interfere with the uptake of protons and Cd by competition forthe carboxyl sites. Whereas the binding mechanism on the carboxyl group was established as an ion exchange process, the second functional group, phosphonate (pK(H) 5.41 +/- 0.31), most likely bound metals by a complexation reaction. A biosorption model was developed based upon the binding mechanisms and was successfully used for predicting the isotherm and pH edge experiments. In addition, the speciation of the binding sites as a function of the pH was simulated using the developed model in order to visualize the distribution of Cd on the binding sites.

Metal selectivity of Sargassum spp. and their alginates in relation to their alpha-L-guluronic acid content and conformation.

The discovery of a consistent and unusual enrichment in homopolymeric alpha-L-guluronic acid G-blocks in alginates extracted from a suite of Sargassum brown algae is described in this study. 1H NMR spectroscopy was used to characterize these alginates which display homopolymeric guluronic acid block (G-block) frequency values (F(GG)) between 0.37 and 0.81. The presence of these G-blocks results in an enhanced selectivity for cadmium or calcium relative to monovalent ions such as sodium and the proton as well as smaller divalent ions such as magnesium. Results of competitive exchange experiments for the Cd-Ca-alginate system yield selectivity coefficient, K*(Cd)Ca, values between 0.43 +/- 0.10 and 1.32 +/- 0.02 for a range in F(GG) of 0.23 to 0.81. In contrast to the Cd-Ca-alginate system, the Mg-Ca-alginate and Mg-Cd-alginate systems yielded maximum values of K*(Mg)Ca (18.0 +/- 1.4) and K*(Mg)Cd (16.0 +/- 0.9) for the alginates extracted from Sargassum fluitans (F(GG) = 0.81; Cuba) and Sargassum thunbergii (F(GG) = 0.75; Korea), respectively. Selectivity studies with mixed-metal pair alginate systems highlight the importance of the specific macromolecular conformation of the alginate polymer in determining metal binding behavior in multiple-metal systems. Furthermore, they demonstrate the importance of the conformation of the alginate as it occurs within the tissue of Sargassum in determining the metal binding behavior of this algal biosorbent. The unique composition of the alginates present in species of Sargassum may represent a distinct advantage over other brown algal species when considering their implementation for the strategic removal of toxic heavy metals from contaminated and industrial wastewaters.