Photodegradation of azo dye Acid Red 18 in a quartz labyrinth flow reactor with immobilized TiO2 bed

The photocatalytic oxidation of azo dye Acid Red 18 in water in the quartz labyrinth flow reactor with immobilized catalyst bed was investigated. A commercially available titanium dioxide (Aeroxide® P25, Degussa, Germany) was used as a photocatalyst. The influence of various factors, including reaction mixture flow rate, initial dye concentration and time of the irradiation on the photodegradation of model compound were examined. The reaction rate was affected by the circulation flow rate, particularly when the flow rate was low (i.e. 4.3 dm3/h). The decomposition rate of Acid Red 18 depended on the initial dye concentration. The rate constants calculated for dye concentrations of 10 and 30 mg/dm3 amounted to 0.228 and 0.176 h−1, respectively. Not only decolorization but also mineralization was effective in the proposed system. After a total fading of the dye solution, ca. 98% of TOC disappeared when the 10 mg/dm3 solution was applied and ca. 99% when 30 mg/dm3 was used. An important advantage of the photoreactor is that no separation of the catalyst is necessary and as a result the size of installation could be minimized and running costs decreased.