Biomedical subjects

Rose Amal

Publications and source records attributed to Rose Amal.

9 recordsLinked to original sources

PubMed2006

Microbial reduction of hexavalent chromium by landfill leachate.

The reduction of hexavalent chromium (Cr(VI)) in municipal landfill leachates (MLL) and a non-putrescible landfill leachate (NPLL) was investigated. Complete Cr(VI) reduction was achieved within 17 days in a MLL when spiked with 100 mg l(-1) Cr(VI) or less. In the same period, negligible Cr(VI) reduction was observed in NPLL. In MLL, Cr(VI) reduction was demonstrated to be a function of initial Cr(VI) concentration and bacterial biomass and organic matter concentrations. The bacteria were observed to tolerate 250 mg l(-1) Cr(VI) in MLL and had an optimal growth activity at pH 7.4 in a growth medium. The MLL also possessed an ability to sequentially reduce Cr(VI) over three consecutive spiking cycles.

Bacteria↗

PubMed2005

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC.

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.

Adsorption↗

PubMed2005

Understanding selective enhancement by silver during photocatalytic oxidation.

The superiority of silver deposited titania particles over bare titania particles for the photocatalytic oxidation of selected organic compounds is explained: the presence of silver mainly enhances the photocatalytic oxidation of organic compounds that are predominantly oxidised by holes, while it has only an insignificant effect on those organic compounds that require hydroxyl radicals for their mineralisation.

Journal Article↗

PubMed2005

Evaluating the applicability of regulatory leaching tests for assessing the hazards of Pb-contaminated soils.

Soil contamination is a major environmental problem due to the ecological threat it poses. In this work, electron probe microanalysis (EPMA), X-ray diffraction (XRD), and leaching studies were employed to explain the different leaching behaviors of non-stabilized and stabilized soils. The applicability of the leaching fluids used in the toxicity characteristic leaching procedure (TCLP) and Australian Standards, AS 4439.1-1997 for assessing the hazards of contaminated soils was investigated as was the leaching of lead from soil stabilized by cement and buffered phosphate techniques. The results showed Pb speciation in the soil highly influenced metal leaching. The synthetic leaching fluids were unable to provide a reliable estimation of Pb concentration in the municipal landfill leachate (ML) due to the absence of organic ligands capable of forming stable complexes with the lead. Water provided the closest representation of lead leaching from the non-stabilized and phosphate stabilized soils while sodium tetraborate buffer was found to be suitable for cement-stabilized soil in a non-putrescible landfill leachate system. A comparison of stabilization methods revealed that the buffered phosphate technique was more suitable for stabilizing the lead in the soil relative to cement stabilization.

Environmental Pollution↗

PubMed2004

Floc strength characterization technique. An insight into silica aggregation.

This paper tests an approach to the estimation of relative particle bond strength based on the nondimensional floc and aggregation factors. The strength of flocs formed by aggregating nanosized silica particles with the addition of potassium chloride (KCl) or cationic surfactants, alkyltrimethylammonium bromide (mixture of CTAB, DTAB, and MTAB) was analyzed. The bonding force of the flocs formed in surfactant compared to that formed in the KCl system was estimated using the new dimensional analysis approach. This force ratio was then compared to that obtained by atomic force microscopy.

Journal Article↗

PubMed2004

Comparison between acetic acid and landfill leachates for the leaching of Pb(II), Cd(II), As(V), and Cr(VI) from cementitious wastes.

The Toxicity Characteristic Leaching Procedure (TCLP) has been widely used to characterize the suitability of solid wastes for disposal in landfills. However, the widespread application of this test for the assessment of wastes disposed in different landfill types is often questionable. This paper investigates the leaching profiles of cement-stabilized heavy metal ions, namely, Pb (II), Cd (II), As(V), and Cr(VI), using acetic acid and leachates from municipal and nonputrescible Australian landfill sites. The leaching profiles of Pb, Cd, As, and Cr using acetic acid were found to be similar to the nonputrescible landfill leachate and differed markedly from the municipal solid waste (MSW) leachate. The additional presence of high amounts of organic and inorganic compounds in the municipal landfill leachate influenced the leaching profiles of these metal ions as compared to the acetic acid and the nonputrescible systems. It is postulated that the organic compounds present in the municipal landfill leachate formed complexes with the Pb and Cd, increasing the mobility of these ions. Moreover, the organic compounds in the municipal landfill leachate induced a reducing environment in the leachate, causing the reduction of Cr(VI) to Cr(III). It was also found that the presence of carbonates in the municipal landfill leachate affected the stability of calcium arsenate, with the carbonate competing with arsenate for calcium at high pH, forcing arsenate into the solution.

Acetic Acid↗

PubMed2003

Evaluating the applicability of a modified toxicity characteristic leaching procedure (TCLP) for the classification of cementitious wastes containing lead and cadmium.

Having the toxicity characteristic leaching procedure (TCLP) as a starting point, this study examined the effect of the various leaching parameters on the leaching of Pb and Cd from cementitious wastes. Using modified TCLP procedures, the parameters investigated were the acid concentration, leaching duration, particle size of the crushed waste, liquid to solid ratio, and the acid type. The main finding was that the final leachate pH controls the leachability of metals due to its influence on their solubility. The high alkalinity of cementitious waste buffers the leachate at a pH where most metals become insoluble. The TCLP was found to result in an unrealistic condition for cementitious wastes due to the high resultant leachate pH.

Cadmium↗

PubMed2001

Scattering Behavior of Restructured Aggregates: A Simulation Study.

Simulations of diffusion-limited cluster-cluster aggregation (DLCA) with no restructuring, full restructuring, and partial restructuring have been performed. The scattering patterns produced from these aggregates have been simulated using the Rayleigh-Gans-Debye approximation. Pure DLCA aggregates produced a scattering pattern with the slope of the fractal region being about -1.8. In contrast, the slope of the fractal region of the scattering pattern for fully restructured aggregates was about -2.1, indicating an increase in fractal dimension. Partial restructuring at large length scales produced an upward turn in the scattering pattern at low qr(o), while at high qr(o) the fractal section of the pure DLCA aggregate was retained. This last result was expected and is consistent with the results and postulations of several other workers. This simulation shows that the type of scattering pattern often obtained from orthokinetic or sheared aggregation can be produced by restructuring of aggregates at large length scales. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Evidence of Shear Rate Dependence on Restructuring and Breakup of Latex Aggregates.

Small-angle static light scattering has been used to probe the evolution of aggregate size and structure in the shear-induced aggregation of latex particles. The size of aggregates obtained from the particle-sizing instrument (Coulter LS230) was compared with the size of those obtained with another approach utilizing the Guinier equation on the scattering data. Comparison of the two methods for studying the effects of mixing on the evolution of the aggregate size with time revealed similar trends. The aggregate structures were quantified in terms of their fractal dimensions on the grounds of the validity of Rayleigh-Gans-Debye scattering theory for the fractal aggregates. Analysis of the scattering patterns of aggregates verified that restructuring of the aggregates occurred as the aggregates were exposed to certain shear environments, resulting in a scale-dependent structure that could not be quantified by a fractal dimension. The effect of restructuring on aggregate size was particularly noticeable when the aggregates were exposed to average shear rates of 40 to 80 s(-1), whereas no significant restructuring occurred at lower shear rates. At 100 s(-1), the fragmentation of aggregates appeared to be more significant than aggregate compac-tion. Copyright 2001 Academic Press.

Journal Article↗