Environmentally benign hybrid nanocomposite beads for azo dye remediation via synchronized dual degradation mechanisms.

Practically, 12% of used dyes are excluded as waste in the mobile aqueous environment. Methyl orange (MO), an industrial azo dye, is known to be carcinogenic. Accordingly, this work was engaged to fabrication of a high-efficiency visible light photocatalysts based on Ag-Alginate/Chitosan-coated MgO nanocomposite beads. MgO and Ag were prepared via precipitation and γ-radiation reduction technique as a green physical one, respectively. The degradation mechanisms depended on catalytic reduction by means of sodium borohydride/Ag and photooxidative degradation. XRD proved the periclase crystalline form of MgO of size 20 nm and the formation of face-centered cubic silver crystals of size 15 nm. The degradation yield varied directly with time, MgO, and dye concentration until certain limit. Five and twenty minutes were enough to get clear solution of MO (30 and 15 ppm, respectively) while 60 min was required to achieve the same target for 60 ppm MO solution. The catalysts showed high efficiency for MO of high concentration. The incorporation of Ag into catalytic beads could support both mechanisms as it could elevate the degradation efficiency up to 50% and save the time to a great extent. Thus, this carrier fruitfully converted wastewater into an effluent that can be repaid to the water cycle with minimal strike on the ecosystem.

Advantages of using non-isothermal bioreactors in agricultural waste water treatment by means of immobilized urease. Study on the influence of spacer length and immobilization method.

The behavior of three different catalytic membranes, obtained by immobilizing urease on nylon sheets chemically grafted with methyl methacrylate, was studied in a bioreactor operating under isothermal and non-isothermal conditions. Membrane activation was carried out by condensation or acyl azide reaction, and spacers of different lengths, such as hexamethylendiamine or hydrazine, were used. Under isothermal conditions, the activities of the catalytic membranes and soluble urease were characterized as a function of pH, temperature, and urea concentration. Both enzyme forms showed the same optimum pH, whereas the optimum temperature was lower for the immobilized enzymes. The spacer length appeared to determine broader pH- and temperature-activity profiles for the urease derivatives. The apparent K(m) values of the insoluble urease were dependent on membrane type and were higher than those of the soluble counterpart, thus indicating an affinity loss for urea. Under non-isothermal conditions, all membranes exhibited an increase of percentage activity proportional to the applied temperature difference and decreasing with the increase of urea concentrations. A decrease of the apparent K(m) was also observed. These results suggest that substrate diffusion limitations due to the immobilization process can be overcome in the presence of temperature gradients. In addition, the remarkable reduction of the production times supports the use of non-isothermal bioreactors for the treatment of urea-polluted waste waters.