Preparation of mesoporous activated carbon from date stones for the adsorption of Bemacid Red.

This work concerns the elimination of the organic pollutant; Bemacid Red (BR), a rather persistent dye present in wastewater from the textile industry in western Algeria, by adsorption on carbon from an agricultural waste in the optimal conditions of the adsorption process. An active carbon was synthesized by treating an agro-alimentary waste, the date stones that are very abundant in Algeria, physically and chemically. Sample after activation (SAA) with phosphoric acid was highly efficient for the removal of BR. The characterization of this porous material has shown a specific surface area that exceeds 900 m2/g with the presence of mesopores. The iodine value also indicates that the activated carbon obtained has a large micro porosity. The reduction of the infrared spectroscopy (FTIR) bands reveals that the waste has been synthesized and activated in good conditions. Parameters influencing the adsorption process have been studied and optimized, such as contact time, adsorbent mass, solution pH, initial dye concentration and temperature. The results show that for a contact time of 60 min, a mass of 0.5 g and at room temperature, the adsorption rate of the BR by the SAA is at its maximum. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were studied to analyse adsorption kinetics. The result shows the adsorption kinetic is best with the pseudo-second-order model. In this study, Langmuir, Freundlich and Temkin isotherms were investigated for adsorption of BR onto SAA. The Freundlich and Temkin isotherms have the highest correlations coefficients. The suggested adsorption process involves multilayer adsorption with the creation of chemical bonds. The mechanism of adsorption of BR by SAA is spontaneous and exothermic, and the Gibbs free energy values confirm that the elimination of the textile dye follows a physisorption.

Experimental and numerical study of methylparaben decomposition in aqueous solution using the UV/H2O2 process.

The present paper aims at presenting a kinetic model that is supposed to result in the decomposition of methylparaben in completely mixed batch reactor (CMBR) using the UV/H2O2 process. The proposed model incorporates photochemical, chemical reactions and their constant rates to formulate the overall kinetic rate expressions which are integrated into MATLAB. Thus, the changes in pH values during the process of oxidation are taken into consideration. In addition, the effects of hydrogen peroxide (HP) dosage, as well as the concentration of hydroxyl radicals, are examined. Accordingly, the pseudo-first-order rate constant, its variation as functions of HP concentration, incident UV-light intensity and the limitations of the adopted approach are discussed. In line with that, the authors provided evidence of the validity of the kinetic model through the exposure of previous experimental studies as reported in the literature review then through the evidence of the present experimental data.

Evidence of colloidal transport of PAHs during column experiments run with contaminated soil samples.

Brownfield soils may contain high levels of organic pollutants particularly polycyclic aromatic hydrocarbons (PAHs). It is essential to predict their migration and fate and to evaluate the risk of transfer to sensitive targets, such as water resources, ecosystems and human health. In this study, soil samples have been taken from an experimental contaminated site of former steel activities located at Homecourt (Lorraine, France). These samples have been lixiviated in laboratory column in water-saturated condition at room temperature. The effluent has been collected by fraction and analysed by a standard method giving total concentration of each of 16 PAHs. The breakthrough curves of 16 PAHs significantly evolve in the same way according to the volume of effluent and tend to vanish to 12-15 pore volumes. If several PAHs remain at a concentration below the solubility, others clearly exceed this threshold. Material balance sheets show that only a very small fraction of PAHs is mobilised. These results are interpreted by postulating that PAHs are transported by the solution not only in the dissolved state but also by associations with particulate or dissolved organic matter.

Dynamic speciation analysis of atrazine in aqueous latex nanoparticle dispersions using solid phase microextraction (SPME).

Solid phase microextraction (SPME) is applied in the dynamic speciation analysis of the pesticide atrazine in an aqueous medium containing sorbing latex nanoparticles. It is found that the overall rate of extraction of the analyte is faster than in the absence of nanoparticles and governed by the coupled diffusion of free and particle-bound atrazine toward the solid/sample solution interface. In the eventual equilibrium the total atrazine concentration in the solid phase is dictated by the solid phase/water partition coefficient (K(sw)) and the concentration of the free atrazine in the sample solution. These observations demonstrate that the nanoparticles do not enter the solid phase. The experimental data show that the rate of release of sorbed atrazine from the latex particles is fast on the effective time scale of the microextraction process. A lability criterion is derived to quantitatively describe the relative rates of these two processes. All together, the results indicate that SPME has a strong potential for dynamic speciation analysis of organic compounds in media containing sorbing nanoparticles.

Steady-state diffusion regime in solid-phase microextraction kinetics.

The temporal evolution of diffusion-controlled analyte accumulation in solid-phase microextraction (SPME) is critically discussed in terms of the various aspects of steady-state diffusion in the two phases under conditions of fast exchange of the analyte at the solid phase film/water interface. For partition coefficients (K(sw)) much larger than unity and a sufficiently thin polymer film, the concentration gradient of the analyte in the polymer phase is largely insignificant. The growth of the accumulated amount of analyte is then adequately described by the well-known exponential expression for steady-state diffusion under non-depletive conditions, provided the initial transient stage is properly taken into account. In case of fiber-type solid phases, the cylindrical nature of the diffusion complicates the nature of the transient stage as well as the magnitude of the steady-state flux.

PAHs and organic matter partitioning and mass transfer from coal tar particles to water.

The coal tar found in contaminated soils of former manufactured gas plants and coking plants acts as a long-term source of PAHs. Organic carbon and PAH transfer from coal tar particles to water was investigated with closed-looped laboratory column experiments run at various particle sizes and temperatures. Two models were derived. The first one represented the extraction process at equilibrium and was based on a linear partitioning of TOC and PAHs between coal tar and water. The partition coefficient was derived as well as the mass of extractable organic matter in the particles. The second model dealt with mass transfer. Particle diffusion was the limiting step; organic matter diffusivity in the coal tar was then computed in the different conditions. A good consistency was obtained between experimental and computed results. Hence, the modeling of PAH migration in contaminated soils at the field scale requires taking into account coal tar as the source-term for PAH release.