M.A. Nawi

Enhancement of azo dye Acid Orange 7 removal in newly developed horizontal subsurface-flow constructed wetland.

Horizontal subsurface-flow (HSF) constructed wetland incorporating baffles was developed to facilitate upflow and downflow conditions so that the treatment of pollutants could be achieved under multiple aerobic, anoxic and anaerobic conditions sequentially in the same wetland bed. The performances of the baffled and conventional HSF constructed wetlands, planted and unplanted, in the removal of azo dye Acid Orange 7 (AO7) were compared at the hydraulic retention times (HRT) of 5, 3 and 2 days when treating domestic wastewater spiked with AO7 concentration of 300 mg/L. The planted baffled unit was found to achieve 100%, 83% and 69% AO7 removal against 73%, 46% and 30% for the conventional unit at HRT of 5, 3 and 2 days, respectively. Longer flow path provided by baffled wetland units allowed more contact of the wastewater with the rhizomes, microbes and micro-aerobic zones resulting in relatively higher oxidation reduction potential (ORP) and enhanced performance as kinetic studies revealed faster AO7 biodegradation rate under aerobic condition. In addition, complete mineralization of AO7 was achieved in planted baffled wetland unit due to the availability of a combination of aerobic, anoxic and anaerobic conditions.

Immobilized titanium dioxide/powdered activated carbon system for the photocatalytic adsorptive removal of phenol

Titanium dioxide (TiO2) and powdered activated carbon (PAC) were fabricated via a layer by layer arrangement on a glass plate using a dip-coating technique for the photocatalytic-adsorptive removal of phenol. Thinner TiO2 layer coated on PAC sub-layer has larger surface area and better phenol removal than the thicker TiO2 layer. The system obeyed the Langmuir isotherm model, which exhibited a homogeneous and monolayer adsorption with a maximum capacity of 27.8 mg g-1. The intra-particle diffusion was the rate-limiting step as the linear plot crossed the origin, while the adsorption was unfavorable at elevated temperature. Under light irradiation, the TiO2/PAC system removed phenol two-times more effectively than the TiO2 monolayer due to the synergistic effect of photocatalysis by TiO2 top layer and adsorption by PAC sub-layer. The COD removal of phenol was rapid for 10mg L-1 of concentration and under solar light irradiation. It was shown that the PAC sub-layer plays a significant role in the total removal of phenol by providing the adsorption sites and slowing down the recombination rate of charge carriers to improve the TiO2 photocatalytic oxidation performance.

Physical and adsorptive characterizations of immobilized polyaniline for the removal of methyl orange dye

Synthesized polyaniline (PANI) powder mixed with ENR-PVC polymer blend adhesive was immobilized on glass plates for the adsorption of methyl orange (MO) dye. The immobilized PANI composite was made up of plasticized PANI aggregates and was in a doped state. The incorporation of ENR-PVC blend in PANI slightly reduced the surface area from 9.2 to 8.5 m2 g-1, and its presence was confirmed through FTIR. The adsorption process was highly dependent on the aeration rate, and the pH of MO solution in which 40 mL min-1 and ambient pH (6.5) was selected as the working conditions. The process of MO uptake onto the immobilized PANI obeyed the pseudo-second-order kinetic model, while intra-particle diffusion was found to dominate the adsorption process. The qm of the immobilized PANI was 77.3 mg g-1 for MO uptake and obeyed the Freundlich isotherm model. The thermodynamic study revealed that the adsorption process of immobilized PANI was spontaneous and unfavorable at high temperature. The immobilized PANI was found to be comparable with other PANI based adsorbents in term of cost, recyclability and adsorption efficiency.