The degradation of textile wastewater and brilliant red dye solutions in a coil photoreactor provided with recirculation, assisted by powdered TiO ₂ and medium-pressure mercury lamp irradiation, was investigated. Factorial design was used for the attainment of the best conditions for COD and color abatement. pH and TiO₂ loading showed to be critical variables for the photocatalytic degradation process for both textile wastewater and aqueous reactive dye solutions (25 mg L^-1). For both substrates, the optimized process conditions by factorial design were almost the same (pH 2-3, 444 mg TiO₂ L^-1 loading, 5 L h^-1 recirculation flow-rate). A 41% COD abatement for textile wastewater was obtained with a 120 min treatment. For the Brilliant Red dye solutions, a 20 min treatment resulted in about 90% decolorization (517 nm, pH 5), as well as in a reduction of 66% of the integrated absorbance (200-600 nm, pH 5).