Modeling the sorption of metal ions from aqueous solution by iron-based adsorbents.

The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy metal ions from aqueous solutions was the aim of the present review paper. Synthesized material was used in two forms, i.e. in fine powder of nanocrystals and in the form of grains (as granular). The main examined parameters were the quantity of sorbent, the presence of ionic strength, the pH value of solution and the metals speciation, including the presence of complexing agents. The removal efficiency of the packed-bed column was examined and compared. Typical adsorption models were discussed and the bed depth-service time equation has been applied to the sorption results in order to model the column operation.

Removal of zinc ion from water by sorption onto iron-based nanoadsorbent.

Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solution (i.e. effluent) by sorption onto synthetic nanocrystalline akaganéite. Due to favorite characteristics, this material was shown to be a promising inorganic adsorbent prepared in the laboratory, following a new method of synthesis-previously published. The effects of adsorbent amount, zinc concentration, solution pH value, ionic strength and temperature variation on the treatment process were mainly investigated during this study. Typical adsorption models were determined searching the mechanism of sorption while the bed depth-service time model was applied to column (with granular material) experiments.

Adsorptive removal of arsenites by a nanocrystalline hybrid surfactant-akaganeite sorbent.

Removal of toxic arsenite ions from aqueous solutions was investigated using an innovative hybrid nanocrystalline surfactant-modified akaganeite. This sorbent was prepared using ferric chloride as the precursor and a cationic surfactant, hexadecyltrimethylammonium bromide. From the experimental work, the material was found to be an effective adsorbent for the separation of arsenites. The chemical kinetics of the process was studied, described by a pseudo-second-order equation. The Freundlich adsorption isotherm was determined to examine the mechanism of sorption. FTIR measurements and XPS analysis gave useful information both on the sorbent synthesized and on the arsenite removal process.

Coagulation-flocculation pretreatment of sanitary landfill leachates.

Sanitary landfill leachates are considered as heavily polluted industrial wastewaters, presenting significant time and spatial variations of their physical-chemical parameters. Special care is required for their efficient treatment and disposal. The main aim of this work was to examine the application of coagulation-flocculation for the treatment of raw and partially stabilized leachates. Jar-test experiments were employed in order to determine the optimum conditions for the removal of organic matter and color, i.e. coagulant-flocculant combination, effective dosage and pH control. Ferric chloride, aluminium sulphate and lime were tested as conventional coagulants, whereas four commercial polyelectrolytes were co-examined: one anionic, two cationic and a non-ionic polymer. High chemical oxygen demand (COD) removal capacities (about 80%) were obtained during the addition of ferric chloride to the partially stabilized leachates, whereas low COD reductions (i.e. lower than 35%) were measured during the addition of coagulants in the raw samples. The addition of polyelectrolytes and pH adjustment in the alkaline region were found to affect slightly the removal of pollutants. The physico-chemical process may be used as a useful pretreatment step, especially for fresh leachates, prior to biological treatment, or as a post-treatment (polishing) step for partially stabilized leachates.

Hybrid flotation--membrane filtration process for the removal of heavy metal ions from wastewater.

A promising process for the removal of heavy metal ions from aqueous solutions involves bonding the metals firstly to a special bonding agent and then separating the loaded bonding agents from the wastewater stream by separation processes. For the separation stage, a new hybrid process of flotation and membrane separation has been developed in this work by integrating specially designed submerged microfiltration modules directly into a flotation reactor. This made it possible to combine the advantages of both flotation and membrane separation while overcoming the limitations. The feasibility of this hybrid process was proven using powdered synthetic zeolites as bonding agents. Stable fluxes of up to 80l m(-2)h(-1) were achieved with the ceramic flat-sheet multi-channel membranes applied at low transmembrane pressure (<100 mbar). The process was applied in lab-scale to treat wastewater from the electronics industry. All toxic metals in question, namely copper, nickel and zinc, were reduced from initial concentrations of 474, 3.3 and 167mg x l(-1), respectively, to below 0.05 mg x l(-1), consistently meeting the discharge limits.

Sorption of As(V) ions by akaganéite-type nanocrystals.

A priority pollution problem, the removal of arsenate oxyanions from dilute aqueous solutions by sorption onto synthetic akaganéite (beta-FeO(OH)) was the aim of the present study. This is an innovative inorganic adsorbent material prepared in the laboratory, following a new method of preparation. The effect of akaganéite and arsenate concentration, the contact time, temperature, solution pH value, and ionic strength variation on the treatment process was mainly investigated during this study. Typical adsorption isotherms were determined, which were found to fit sufficiently the typical Langmuir equation. The mechanism of sorption was examined by electrokinetic, X-ray diffraction, Fourier transmission infrared and scanning electron microscopy measurements. Promising results were obtained, due to the favourite characteristics of the adsorbent applied.

Flotation of metal-loaded clay anion exchangers. Part II: the case of arsenates.

Hydrotalcite-like materials, or otherwise termed layered double hydroxides, are clays with an ability to remove anions. As they usually are in powder form, these sorbents often present appreciable problems in the solid/liquid separation process following the sorption stage. Sorptive flotation of metal-loaded particles was investigated in this paper, as an alternative two-stage process. In the sorption process, satisfactory removals of arsenic(V) were obtained onto synthetic hydrotalcite particles from water. The effect of some parameters, like the solution ionic strength, concentrations, temperature, etc. was examined. During the second stage of the process, hydrotalcite fine particles were removed from the liquid phase by dispersed-air flotation; various surfactants were tested in relation to the ionic strength of the solution. The combined process of sorptive flotation provides promising results for arsenic removal.

A kinetic model describing cell growth and production of highly active, recombinant ice nucleation protein in Escherichia coli.

A structured kinetic model, which describes the production of the recombinant ice nucleation protein in different conditions, was applied. The model parameters were estimated based on the variation of the specific growth rate and the intracellular product concentration during cultivation. The equations employed relate the cellular plasmid content or plasmid copy number with the cloned-gene expression; these correlations were successfully tested on the experimental data. The optimal nutrient conditions for the growth of Escherichia coli expressing the inaZ gene of Pseudomonas syringae were determined for the production of active ice nucleation protein. The kinetics of the cultures expressing the inaZ gene were studied in a bioreactor at different growth temperatures and nutrient conditions.

Modelling the sorption of metals from aqueous solutions on goethite fixed-beds.

The research on separation methods of toxic metals from wastewater streams is continuous and intensive and, among them, sorption processes are considered of particular importance, mainly due to their effectiveness. The sorption of chromate anions and zinc cations from dilute aqueous solutions using a packed-bed (column configuration) of synthesised granulated goethite was investigated in the present study. The examined parameters during this investigation were the following: (1) the initial pH value of metal-laden aqueous solution (two representative values at acidic pH, 3.5 and 5.0, were tested); (2) the quantity of sorbent in the column, corresponding to bed height; and (3) the influence of ethylene diamine tetra acetic acid (EDTA) addition, a common, strong chelating agent. The Bed Depth-Service Time model has been applied to the sorption results in order to model the column operation. The removal efficiency of Cr(VI) anions by the sorptive column was found to be higher than that of Zn(II) cations. The presence of EDTA caused a certain decrease of removal efficiency for the case of hexavalent chromium, due to competition for the same sorption sites, while the removal of divalent zinc was increased, due to variation of cation speciation.

Biosorptive flotation for metal ions recovery.

The solid/liquid separation of suspended, metals-loaded biomass was studied extensively by successfully applying flotation. Industrial non-living biomass samples of different origin have been tried in the laboratory as sorbents of metal ions, with the main stress on Streptomyces rimosus, an effective actinomyces. Flotation was used as the harvesting technique downstream, following the biosorption stage. Important parameters of the investigation were the solution pH, the surfactant type and concentration, the applied modification of biomass, etc. The reuse and recycling of biosorbent following elution was proved possible. As a result cleaned water was produced as underflow of the flotation process.

Flotation of metal-loaded clay anion exchangers. Part I: the case of chromates.

Synthetic hydrotalcite-like layered materials are known for their ability to remove anions, like the chromates. These sorbents usually exist in powder form, thereby exhibiting high surface area and rapid kinetics for adsorption, but presenting appreciable problems in the subsequent solid/liquid separation process. Almost complete removals were obtained in this paper, from batchwork dispersed-air flotation in presence of a flocculant. Due to the experienced difficulty of flotation of thermally activated (at 500 degrees C) hydrotalcite metal-loaded particles, the application of various surfactants was studied. Continuous-flow laboratory runs certified also the effectiveness of this combined process of sorptive flotation, a promising innovative treatment technology.

Flotation removal of As(V) onto goethite.

Arsenic oxyanions, considered as priority pollutants, were removed from dilute aqueous solutions by sorption onto synthetic goethite, a typical inorganic adsorbent. Flotation was subsequently applied as an effective solid/liquid separation method. The combined process produced a foam concentrate, containing the arsenic-loaded goethite particles. The dispersed-air flotation technique was used for the generation of fine gas bubbles. The main parameters affecting the process were studied and promising results, in terms of arsenic removal and of goethite separation, were obtained.

Metal biosorption-flotation. Application to cadmium removal.

Biosorption using suspended non-living biomass, and flotation (for consequent solid/liquid separation of the metal-loaded biomass) have been studied in the laboratory as a possible combined process, for the removal of toxic metals (i.e., cadmium) from dilute aqueous solutions. The various parameters of the process were investigated in depth, including re-use of biosorbent. A filter aid (contained in the biomass industrial waste used) was found not really to interfere. Zeta-potential measurements of the aforementioned system were also carried out. Promising results were obtained during continuous-flow experiments. A flotation residence time of 4 min was achieved. Metal removal and suspended biomass recovery were generally over 95%.

Flotation of cadmium-loaded biomass.

Biosorption of heavy metal ions such as Cd(2+) by dead biomass has been recognized as a potential alternative to existing removal technologies applied to wastewater treatment. Two bacterial strains were studied in the laboratory, streptomyces griseus and S. clavuligerus, an industrial by-product. Both washed and unwashed samples were examined. Foam flotation proposed in this work as the separation state following biosorption. Effective biomass separation was conducted in the presence of a frother, ethanol. The pH of the solution was a crucial parameter for flotation and also for metal binding. Other basic parameters of flotation examined were the initial cadmium concentration in the dilute aqueous solution and the quantity of biomass used. A study of zeta-potential measurements of the actinomycetes was carried out under the conditions used in the separation; surface tension was also measured. These provided useful information on the process.