Enhanced degradation of dyes in secondary textile wastewater: Continuous-flow photoreactors using TiO2/chitosan/glycerol under UVA irradiation

One of advanced methods for treating textile wastewater is photocatalytic processes that decolorize and degrade organic pollutants. In this study, a photoreactor using TiO 2 /chitosan/glycerol (TCG) beads under ultraviolet A (UVA) irradiation was employed to degrade acid blue 193 (AB193) and treat secondary textile wastewater (STWW). The photoreactor's dye removal efficiency was evaluated by varying fixed TCG thickness, initial dye concentration, and hydraulic retention time. Optimal dye removal was achieved at 15 min in batch mode with fixed TCG thicknesses of 0.75–1.25 cm. The apparent rate constant ( k app ) increased with initial dye concentration, indicating that the degradation process followed pseudo-first-order kinetics. The continuous-flow system exhibited lower removal efficiencies and rate constants ( k r ) than the batch system, with k r decreasing from 0.841 to 0.781 as the fixed TCG thickness increased from 0.75 cm to 1.75 cm. In contrast, the batch system showed a slight increase in k r from 1.010 to 1.034. The batch system outperformed the continuous-flow photoreactor, particularly at high contaminant concentrations. In continuous-flow experiments, STWW decolorization slightly increased from 76.0% to 77.2%, while COD removal decreased from 83.7% to 78.8% with an increase in fixed TCG thickness from 0.75 cm to 1.25 cm. These findings demonstrate that the TCG beads combined with the continuous-flow photoreactor effectively treat textile wastewater, producing effluent that meets Vietnamese environmental standards.