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Most of dyes are considered as non - biodegradable substances and because this, they have became in an environmental problem. Commercial dyes are used in paper and textile industries, and their by-products contaminate surface water sources. Titanium dioxide - based photocatalysis can be an alternative for treatment of dye - contaminated water streams before dumping, because this process can generate powerful oxidant species as hydroxyl free radicals (•OH). In this study, the photocatalytic decolorization of methylene blue was carried out in a compound parabolic collector (CPC) and tubular collector (TC; no reflectors) using the radiation provided by a set of six UV black-lamps. The experimental tests corresponding to a central-composite experimental design were carried out during three hours, whereas the tests for optimal conditions were carried out during 315 min. The decolorization of the dye was measured indirectly with UV- visible absorbance. The optimal region could be determined using the Response Surface Methodology, and for CPC reactor the results were 70.8% for optimal degradation at 0.44 g/L of TiO 2  and a pH of 8.41, whereas for tubular collector the optimal decolorization were 63.46% at 0.38 g/L of TiO 2 , and a pH of 6.34. For both reactors, the optimal conditions found with Response Surface methodology were experimentally validated (66.5% MB decolorization for CPC and 62.1% MB decolorization for TC). With optimal conditions found, the possibility of air sparging was also evaluated. The degradation rate of dye increased slightly with oxygen saturation, whereas it was observed a larger decolorization of dye in CPC reactor than the tubular reactor.

Photocatalytic Decolorization of Methylene Blue with Two Photoreactors