Combining photocatalytic process and biological treatment for Reactive Green 12 degradation: optimization, mineralization, and phytotoxicity with seed germination.

In this study, we show that the combination of a photocatalytic process (as a pretreatment step) combined with the conventional biological treatment of wastewaters can improve the process and achieve satisfactory efficiency. In this context, Reactive Green 12 (RG-12) solutions were photocatalytically pretreated using TiO2-impregnated polyester as supported catalyst under UV light in batch reactor. Photocatalysis as pretreatment (during 4 and 8 h of irradiation) was combined with 7 days of aerobic biological treatment using activated sludge. As first assays, respiratory tests revealed that the removal of RG-12 was improved by 5.4% and 11.7% for the solutions that were irradiated for 4 and 8 h in the presence of TiO2, respectively. However, 34.5% and 19% of dye solution was discolored after 7 days of biological treatment for the pretreated solutions during 4 and 8 h of UV light exposure, respectively. The discoloration efficiency obtained by the combined processes achieved 59.6% and 74.9% for the samples under photocatalysis during 4 and 8 h, respectively. A significant decrease in chemical oxygen demand (COD) of about 74.9% was achieved after photocatalysis/biodegradation processes. In addition, a decrease in the phytotoxicity was obtained as followed by the germination index (GI) values of cress seeds that increased from 46.2 to 88.7% after 8 h of photocatalysis and then to 92.8% after further 7 days of biological treatment.

Box-Wilson design modeling of photocatalytic degradation of industrial dye and wastewater in semi-pilot solar photoreactor.

This work focuses on the treatment of a dye solution, C.I. Basic Blue 41 (BB41), and industrial wastewater by UV/TiO2 photocatalytic process using aqueous catalyst suspensions of titanium dioxide (TiO2), Degussa P25. The procedures were carried out in a semi-pilot scale prototype solar photoreactor under solar radiation. Response surface methodology (RSM) based on Box-Wilson design was applied to assess individual effects of the five main independent parameters: initial dye concentration ([BB41]), TiO2 concentration ([TiO2]), flow rate (Q) initial pH and accumulated solar energy (Qvn) on the decolorization efficiency and to optimise the UV/TiO2 process. Photocatalytic mineralisation was carried out at the optimal conditions found by RSM and results were evaluated by total organic carbon (TOC) abatement for BB41 sloution and industrial wastewater. The optimal conditions found by RSM were: 0.4 g/L, 14.04 mg/L, 1,479.6 L/h, 5.52 and 80 KJ/L for TiO2 concentration, initial dye concentration, flow rate, initial pH and accumulated solar energy, respectively. Photocatalytic mineralisation results show that for accumulated visible solar energy equal to 377.714 kJ/L (after 6 hours of irradiation), under these conditions, the percentage of the initial TOC reduction is about 88% and 85.5% for industrial waste and BB41 solution, respectively.

Efficient degradation method of emerging organic pollutants in marine environment using UV/periodate process: Case of chlorazol black.

Sea has historically been subject to high anthropogenic pressures of direct and indirect loads of emerging organic pollutants (EOPs) from intensive industrial and agricultural activities. Photoactivated periodate (UV/IO4-) is an innovative oxidation technique that was never tested in seawater as pollutants matrix. In this work, we attempted to investigate the treatment of seawater contaminated with chlorazol black (CB) dye, as a model of EOPs, using photoactivated periodate process. It was found that periodate (0.5mM) assisted-UV treatment of CB (20mgL-1) in seawater resulted in 13.16-fold increase in the initial degradation rate, compared to UV alone, and 82% of CB was removed after 40min face to 38% under UV alone. The beneficial effect of UV/IO4- treatment is strongly dependent on operational parameters. More interestingly, SDS surfactant, as an organic matter, did not affect the degradation process, making UV/IO4- a promising technique for treating seawater contaminated with EOPs.