K. A. Matis

Biosorption of toxic metals from aqueous solutions by bacteria strains isolated from metal-polluted soils

The use of biological materials for effective removal and recovery of heavy metals from contaminated wastewaters has emerged as a potential alternative method to conventional treatment techniques. The aim of this paper was the laboratory study of biosorption of toxic metals from aqueous solution by the application of microorganisms (Bacillus laterosporus or Bacillus licheniformis), isolated from polluted (metal-laden) soil. Microorganisms have a high surface area-to-volume ratio, because of their small size and therefore, they can provide a large contact interface, which would interact with metals from the surrounding environment. Microbial metal accumulation has received much attention during recent years, due to the potential use of microorganisms for treatment of metal-polluted water or wastewater streams. Two toxic metals were selected as typical examples: a cation (cadmium) and an oxyanion (hexavalent chromium, and promising results were obtained, under optimized conditions.

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.

REMOVAL OF AS (V) FROM WASTEWATERS BY CHEMICALLY MODIFIED FUNGAL BIOMASS

Biosorption has been demonstrated to be a useful alternative to conventional treatment systems for the removal of toxic metals from dilute aqueous solution. The objective of this paper was to examine the main aspects of a possible strategy for the removal of arsenates, employing P. chrysogenum biomass. The pretreatment of biomass with common surfactants (as hexadecyl-trimethylammonium bromide and dodecylamine) and a cationic polyelectrolyte was found to improve the biosorption efficiency. The initial biomass showed a relative low affinity for metallic anions, whereas with the application of modified samples a significant uptake of arsenic was observed. Sorption data were well described by typical Langmuir and Freundlich adsorption isotherms. Promising results were obtained in laboratory experiments and effective As(V) removals were observed.

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.

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.

Removal of hexavalent chromium anions from solutions by pyrite fines

Abstract Bench scale experiments were conducted in the laboratory, aiming to the removal of hexavalent chromium from aqueous solutions, by dispersed pyrite fine particles. Pyrite (iron sulphide mineral), was found to act as an efficient Cr(VI) reducing agent. The resulted hydroxo-Cr(III) species were found to be precipitated (and removed) onto the pyrite particles. The process mechanism was also examined by ς-potential measurements and speciation studies. Promising results were obtained at highly acidic pH values (around 1–2), showing an interesting aspect of fine (solid waste) mineral particles utilization, in the removal of a priority pollutant.

BIOSORPTION OF CADMIUM IONS BY ACTINOMYCETES AND SEPARATION BY FLOTATION

Among the most important parameters which have to be examined, when treated waste waters are going to be recycled, is their content of toxic metals, due to ever decreasing metal disposal limits. For this reason, the examination of effective and innovate waste water treatment methods becomes an important need. The removal of cadmium, a toxic metal of high environmental priority due to its toxicity, from dilute aqueous solutions has been studied in the present work, applying microorganisms and using living, as well as non-living bacterial biomass of two specially isolated Actinomycetes strains, AK61 and JL322. The main parameters influencing this treatment process, namely contact time, pH of the solution, temperature and toxic metal and biomass concentrations have been examined and Langmuir isotherms have been depicted. Dispersed-air flotation was applied as the subsequent separation method for harvesting the suspended metal-laden microorganisms, following the biosorption of cadmium. The investigated parameters (in batch mode, laboratory scale) were in this case the dispersion pH, the flotation time, the air flowrate and the surfactant concentration. Electrokinetic measurements have been also performed for the biomass dispersions, under similar conditions with biosorption, providing useful information for the process mechanisms. Applying the optimum defined conditions, over 95% removal of cadmium has been achieved in one stage and simultaneously, quantitative separation of the used (metal-loaded) biomass has been obtained.

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.

Flotation of Salt-Type Minerals

Salt-type minerals flotation is discussed, based mainly on experiments on magnesite, dolomite and calcite. Among the parameters affecting flotation, the following are examined : crystal structure, solubility of minerals, surface charge, collectors, organic and inorganic modifiers, adsorption, contact angle and floatability. The selective separation by flotation of salt-type minerals from each other and from silicates is also investigated.

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.