A.I. Zouboulis

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.

Removal of arsenic from contaminated water sources by sorption onto iron-oxide-coated polymeric materials.

The modification of polymeric materials (polystyrene and polyHIPE) by coating their surface with appropriate adsorbing agents (i.e. iron hydroxides) was investigated in the present work, in order to apply the modified media in the removal of inorganic arsenic anions from contaminated water sources. The method, termed adsorptive filtration, has been classified as an emerging technology in water treatment processes as it presents several advantages towards conventional technologies: the production of high amounts of toxic sludge can be avoided and it is considered as economically more efficient; whereas it has not yet been applied in full-scale treatment plants for low-level arsenic removal. The present experiments showed that both modified media were capable in removing arsenic from the aqueous stream, leading to residual concentration of this toxic metalloid element below 10 microg/L, which is the new maximum concentration limit set recently by the European Commission and imposed by the USEPA. Though, among the examined materials, polyHIPE was found to be more effective in the removal of arsenic, as far as it concerns the maximum sorptive capacity before the filtration bed reaches the respective breakthrough point.

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.

A field investigation of the quantity and quality of leachate from a municipal solid waste landfill in a Mediterranean climate (Thessaloniki, Greece)

Abstract Sanitary landfill leachates belonging to different stabilization stages were systematically sampled and 20 of the most commonly examined pollution parameters were determined on a seasonal basis. Selected important relationships between these parameters were defined and statistical evaluation of the results has been performed. The composition of leachates varied widely, depending mainly upon their degree of stabilization and upon their seasonal production, representing the influence of different climatic conditions. All parameters examined showed markedly higher values when leachates were collected ‘fresh’, while pH tended to increase gradually with time from slightly acidic towards alkaline values in leachate that is older, and therefore more stabilized. Toxic metal concentrations were found to be relatively low in ‘fresh’ leachate samples and even lower in the aged ones. Finally, suggestions have been proposed for the subsequent treatment of leachates, based upon hydrological and leachate quality data, in order to avoid environmental deterioration problems caused by direct disposal.

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.

Treatment of oil-in-water emulsions by coagulation and dissolved-air flotation

Abstract The treatment of oil-in-water emulsions containing n-octane (used as simulated wastewater) was investigated by means of dissolved-air flotation jar-tests. The effect of several parameters on flotation efficiency for separation of the emulsified oil was examined, namely, (a) the presence the nonionic surfactant Tween 80, used for the stabilization of the emulsions, (b) the initial pH value of the emulsions, (c) the concentration of chemical additives, such as polyelectrolytes (organic flocculants of cationic or anionic type) or ferric chloride (inorganic coagulant), (d) the concentration of sodium oleate (used as flotation collector) and (e) the recycle ratio. Zeta-potential measurements were also performed in order to interpret the obtained results. The use of polyelectrolytes was not able to effectively treat the studied emulsions, while the addition of ferric chloride and the subsequent application of dissolved-air flotation was found very efficient. At the optimum defined experimental conditions (recycle ratio: 30%, pH: 6, [Fe3+]: 100 mg l−1 and [sodium oleate]: 50 mg l−1) more than 95% of the emulsified oil was effectively separated from an initial concentration of 500 mg l−1.

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.

Comparison of two biological treatment processes using attached-growth biomass for sanitary landfill leachate treatment.

The objective of this investigation was to compare two biological systems using attached-growth biomass, for treatment of leachates generated in a typical municipal solid waste sanitary landfill. A moving-bed biofilm process, which is a relatively new type of biological treatment system, has been examined. It is based on the use of small, free-floating polymeric (polyurethane) elements, while biomass is being grown and attached as biofilm on the surface of these porous carriers. A granular activated carbon (GAC) moving-bed biofilm process was also tested. This method combines both physico-chemical and biological removal mechanisms for the removal of pollutants. The presence of GAC offers a suitable porous media, which is able to adsorb both organic matter and ammonia, as well as to provide an appropriate surface onto which biomass can be attached and grown. A laboratory-scale sequencing batch reactor (SBR) was used for the examination of both carriers. The effects of different operation strategies on the efficiency of these biological treatment processes were studied in order to optimize their performance, especially for the removal of nitrogen compounds and of biodegradable organic matter. It has been found that these processes were able to remove nitrogen content almost completely and simultaneously, the removal of organic matter (expressed as BOD5 and COD), color and turbidity were sufficiently achieved.

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.