A further insight into the mechanism of biosorption of metals, by examining chitin epr spectra.

Experimental chitin-uranium-copper EPR spectra have been simulated by computer. The simulation suggests that the chitin-copper-uranium EPR spectra are primarily due to a chitin-copper interaction, with insignificant contribution from other paramagnetic species. The simulation suggests two possible complex configurations, both involving one ligand nitrogen atom.

The mechanism of metals precipitation by biologically generated alkalinity in biofilm reactors.

Microbial strains, characterized by increased tolerance and ability to grow in metal bearing wastewaters as well as by effective metal sequestering capability by both active (bioaccumulative) and passive (biosorptive) processes, were tested as inoculum for metal laden wastewater treatment systems. Their capacity to grow in metal bearing wastewater, using an easily available and inexpensive carbon source such as acetate, was studied in batch experiments. Two principal conclusions were drawn: (1). Growth was observed for all the strains examined suggesting that the strains can be acclimated to metals bearing wastewaters. (2). Solution pH increased from neutral to alkaline values during growth (pH(initial)=7, pH(final)=10). The later was observed systematically for all strains. Metal precipitation, due to the metabolically generated alkalinity is expected as a result.Supporting evidence for this hypothesis was provided during the operation of two pilot moving bed sand filters treating two different metal bearing wastewaters. Acetate was used as carbon source to support the growth and maintenance of microbial biomass on the sand grains of the filters. The characteristics of the sludge produced from the operation of the pilot plants were subsequently studied in the laboratory. Both sludges were significantly loaded with large amounts of metals.A mechanism of metal precipitation induced by the metabolically generated alkalinity, when acetate is used as carbon source, could be proposed as the main process responsible for the metals sequestering inside the moving bed sandfilter reactor.

An investigation of engineering parameters for the use of immobilized biomass particles in biosorption.

Immobilized, inactive mycelia of Rhizopus arrhizus are preferential to native biomass for use in the biosorption of metal ions. Refinement of a proprietary immobilization technique previously developed at McMaster University enabled production of particles of immobilized Rhizopus arrhizus biomass having a 12-23% wt of polymer additive. The effects of production stage parameters on the intrinsic uptake capacity of the immobilized biomass were examined. Kinetic experiments showed the following trends: a decrease in the weight percent of the added polymer leads to an increase in the apparent uranium uptake capacity of the immobilized biomass particles for a given contact time. A decrease in the particle size improved the kinetics of metal uptake and led to an increase in the apparent uranium uptake capacity for the same contact time. An increase in the initial concentration of the uranium solution caused equilibrium conditions to be attained faster.

PM10 composition during an intense Saharan dust transport event over Athens (Greece).

The influence of Saharan dust on the air quality of Southern European big cities became a priority during the last decade. The present study reports results on PM(10) monitored at an urban site at 14 m above ground level during an intense Saharan dust transport event. The elemental composition was determined by Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) for 12 elements: Si, Al, Fe, K, Ca, Mg, Ti, S, Ni, Cu, Zn and Mn. PM(10) concentrations exceeded the EU limit (50 µg/m(3)) several times during the sampling period. Simultaneous maxima have been observed for the elements of crustal origin. The concentrations of all the elements presented a common maximum, corresponding to the date where the atmosphere was heavily charged with particulate matter permanently for an interval of about 10h. Sulfur and heavy metal concentrations were also associated to local emissions. Mineral dust represented the largest fraction of PM(10) reaching 79%. Seven days back trajectories have shown that the air masses arriving over Athens, originated from Western Sahara. Scanning Electron Microscopy coupled with Energy Dispersive X-ray analysis (SEM-EDX) revealed that particle agglomerates were abundant, most of them having sizes <2 µm. Aluminosilicates were predominant in dust particles also rich in calcium which was distributed between calcite, dolomite, gypsum and Ca-Si particles. These results were consistent with the origin of the dust particles and the elemental composition results. Sulfur and heavy metals were associated to very fine particles <1 µm.

The role of chitin in uranium adsorption by R. arrhizus.

In order to further refine and support the uranium biosorption mechanism hypothesis proposed for Rhizopus arrhizus, uranium competitive equilibrium uptake isotherms by chitin were determined at two different solution pH levels and in the presence of different concentrations of competing ions, namely, Cu(2+), Zn(2+), and Fe(2+). The co-ion effect became more poronounced as the co-ion concentration in solution and pH increased. Obtained equilibrium data are in agreement with uranium biosorption data reported earlier. Infrared, mass, and electron paramagnetic resonance (EPR) spectra of chitin before and after uranium uptake in the presence of the competing ions Cu(2+), Zn(2+), and Fe(2+) were recorded. The combination of the spectral data and the information from equilibrium studies supported the hypothesis advanced earlier on the mechanism of uranium uptake by R.arrhizus. In addition, the data suggested the participation of a free radical in uranium coordination by the cell wall chitin. The mechanism of reduction of the uranium uptake capacity of the biomass in the presence of competing ions was also elucidated further.

The mechanism of uranium biosorption by Rhizopus arrhizus.

Biosorption of elements is a little understood phenomenon exhibited by some types of even nonliving microbial biomass. A common fungus Rhizopus arrhizus has been reported to take up uranium from aqueous solutions to the extent of 180 mg U(6+)/g. The mechanism of uranium sequestering by this type of biomass was studied by using experimental techniques such as electron microscopy, x-ray energy dispersion analysis, IR spectroscopy, and supporting evidence was obtained for a biosorption mechanism consisting of at least three processes. Uranium coordination and adsorption in the cell-wall chitin structure occur simultaneously and rapidly whereas precipitation of uranylhydroxide within the chitin microcrystalline cell-wall structure takes place at a lower rate. Interference of Fe(2+) and Zn(2+) coions with uranium biosorption is indicated.

The mechanism of thorium biosorption by Rhizopus arrhizus.

Inactive cells of Rhizopus arrhizus have been documented to exhibit a high thorium biosorptive uptake (170 mg/g) from aqueous solutions. The mechanism of thorium sequestering by this biomass type was investigated following the same method as for the uranium biosorption mechanism. The thorium sequestering mechanism appeared somewhat different from that of uranium. Experimental evidence is presented which indicates that, at optimum biosorption pH (4), thorium coordinates with the nitrogen of the chitin cell wall network and, in addition, more thorium is absorbed by the external section of the fungal cell wall. At pH 2 the overall thorium uptake is reduced. The kinetic study of thorium biosorption revealed a very rapid rate of uptake. Unlike uranium at optimum solution pH, Fe(2+) and Zn(2+) did not interfere significantly with the thorium biosorptive uptake capacity of R. arrhizus.

Mechanism of aluminum interference on uranium biosorption by Rhizopus arrhizus.

Uranium competitive uptake experiments by Rhizopus arrhizus were carried out at three different solution pH levels and in the presence of different concentrations of competing aluminum ions in order to examine the competing ion effect. The coion effect became more pronounced as the coion concentration in solution and pH level increased. A preliminary examination of the effect of aluminum on the rate of uranium uptake was also completed. Results showed that the presence of aluminum does not interfere with the kinetics of uranium uptake by R. arrhizus. Electron microscopic and energy dispersive X-ray analyses were also performed on samples of the biomass. The combination of spectral data and the information from the equilibrium studies and the kinetic studies suggested that aluminum interferes with the uranium biosorptive uptake capacity of R. arrhizus by the precipitation of a metastable amorphous hydroxy polymeric precipitate through a mechanism we refer to as steric competition.

Adsorption of radium-226 by biological origin absorbents.

Selected samples of waste microbial biomass used in industrial fermentation processes and wastewater biological treatment plants have been studied for their radium biosorption ability from aqueous solutions. Equilibrium biosorption isotherms have been used to quantify the radium uptake capacity of the various types of biomass which were also compared to two types of activated carbon. Solution pH affected the observed uptake significantly. In general, the biomass types that showed appreciable sorption capacity exhibited maximum uptake between pH 7 and 10. The uptake was reduced considerably at pH 4 and little or no uptake was observed at pH 2. Radium biosorptive uptake capacities of the order of 4.5 x 10(4) nCi/g, at pH 7 and at an equilibrium radium concentration of 1000 pCi/L, were determined for a mixed culture, while the biomass of Penicillium chrysogenum adsorbed 5 x 10(4) nCi/g radium under the same conditions. The highest uptake value for a sample of F-400 granular activated carbon was 3600 nCi/g at pH 7 and 1000 pCi/L radium concentration. The biosorptive radium uptake of microbial biomass is compared to literature values for other types of adsorbents. The most effective biomass types studied exhibited radium removals in excess of 99% of the radium in solution.

A batch reactor mass transfer kinetic model for immobilized biomass biosorption.

Inactive cells of Rhizopus arrhizus have been immobilized into the form of particles of desirable particle size using a proprietary immobilization technique. The immobilized biomass particles are porous and are members of a new generation of biological origin adsorbents. The uranium adsorptive behavior of the biosorbent particles was modeled using a batch reactor mass transfer kinetic model of the biosorption process. The model successfully predicts the batch reactor adsorbate (uranium) concentration profiles and has provided significant insights on the way biosorbents function.

The continuous recovery of uranium from biologically leached solutions using immobilized biomass.

The potential of uranium recovery from the dilute uranium ore bioleach solutions of the Elliot Lake district of Canada was examined using immobilized microbial biomass. Batch and continuous laboratory scale pilot plant experiments were carried out. The results have shown that the immobilized microbial biomass can successfully recover all of the uranium from dilute (less than 300 mg U/L) solutions. The uranium can subsequently be eluted producing a high uranium concentration eluate perhaps exceeding 5000 mg U/L. The biomass maintained its biosorption capacity of about 50 mg U/g over 12 examined successive adsorption-elution cycles with no apparent indication of failure.