Abstract. An alternative process for the removal of organic pollutants in aqueous systems is photocatalysis. The challenges hindering its industrial use are electron-hole recombination and mass-transfer limitations. In order to address these problems, the objective of this study is to introduce air by sparging, and design an air-sparged photocatalytic reactor using titanium dioxide immobilized on borosilicate glass. The performance of the reactor on the removal of the model pollutant, methylene blue (MB), was evaluated and compared against the reactor operated without sparging. The effect of mass-transfer limitations on reactor performance was also investigated by regression using a Langmuir-type model equation. The sparged photocatalytic reactor was able to degrade 57% MB in 2 hours, an improvement of 40% compared to no sparging, and is comparable to similar reactors in literature, but with the advantage of using less expensive materials of construction and simpler immobilization technique. Mass-transfer limitation studies showed a good fitting of the initial reaction rate r, with r = 0.1399Q / (0.6120 + Q) for the sparged operation, and Q is the volumetric flowrate of water (L/min). The model also shows that the reactor operates near the reaction-limited regime, and that the extent of mass-transfer limitation effects was reduced by the present reactor.

Abstract-An alternative process for the removal of organic pollutants in aqueous systems is photocatalysis. The challenges hindering its industrial use are electron-hole recombination and mass transfer limitations. In order to address these problems, the objective of this study is to introduce air by sparging, and design an air-sparged photocatalytic reactor using titanium dioxide immobilized on borosilicate glass. The performance of the reactor on the removal of the model pollutant, methylene blue (MB), was evaluated and compared against the reactor operated without sparging. The effect of mass transfer limitations on reactor performance was also investigated by regression using a Langmuir-type model equation. Reactor performance was optimized using Response Surface Methodology to determine the set of initial MB concentration, treatment time, initial pH, and sparging rate that would result to the highest removal of methylene blue. The sparged photocatalytic reactor was able to degrade 57% MB in 2 hours, an improvement of 40% compared to no sparging. Mass transfer limitation studies showed that the reactor operates near the reaction-limited regime, and that the extent of mass transfer limitation effects was reduced. The set of parameters that maximizes methylene blue removal were 2.0 ppm MB, 120 minutes treatment time, pH 9.95 and 2.0 L/min sparging rate, with a predicted removal of 55.5%. Validation experiments resulted to 57.2% MB removal, and that the present reactor is comparable to similar reactors in literature, but with the advantage of using less expensive materials of construction and simpler immobilization technique.Index Terms-Photocatalysis, response surface methodology, tubular photocatalytic reactor, wastewater treatment.