The photocatalytic discoloration of Reactive Blue 19 (RB-19), a textile anthraquinone dye, were investigated in aqueous suspensions containing TiO2 or ZnO as catalysts. The reactions can be mathematically described as a function of parameters pH, amount of catalyst and dye concentration being modeled by the use of response surfaces methodology. Optimized values for the concentration of the catalyst and the pH for each reaction systems were determined. ZnO showed greater degradation activity than TiO2 when the reaction was carried out in a 41 circulating reactor under optimized conditions. The figure-of-merit electric energy per order (EE/O) allows to determine that the electrical energy cost of reducing the color by one order of magnitude was three times higher for TiO2. In both reaction systems, the acute toxicity evolved from zero to around 50 toxicity units in the initial stages of irradiation, depleting to minimal values after 30 min of reaction.