Photocatalytic Degradation of Textile Dyeing Wastewater Using Titanium Dioxide on a Fixed Substrate: Optimization of Process Parameters and Continuous Reactor Tests

Herein, a preparation of a mixed-phase titanium dioxide (TiO 2 ) thin layer on glass beads was developed using the modified spray method. This approach was determined to be affordable and easy to operate. Optimum conditions were investigated for the photodegradation of wastewater generated from textile dyeing by TiO 2 -coated glass beads as a catalyst using the central composite design (CCD). An increase in the direct dye photodegradation rate was observed at lower direct dye concentrations when TiO 2 dosages were increased, and the initial pH value was decreased. The optimal conditions involving TiO 2 dosage, pH, UV intensity, and dye concentrations were 3 g/L, 5.0, 3000 µW/cm 2 , and 50 mg/L, respectively, when administered at ambient temperatures. For the batch experiments, the direct dye removal efficiency at 93.7% was achieved within 24 h. The average direct dye removal efficiency was 67.8% and could be up to 80.2% when using a fixed-bed photocatalysis reactor during 30 d of continuous operation. The reused catalyst’s degradation efficiency was not significantly changed, indicating its capability for repeated reuse and the excellent stability of immobilized TiO 2 onto the glass beads. This study additionally found that high temperatures could increase the efficiency of color removal.