Kinetics and mass transfer of fixed bed photoreactor using N-doped TiO₂ thin film for tannery wastewater under visible light

A fixed bed photocatalytic reactor with N-doped TiO₂ thin film coated on stainless steel plate was conducted for tannery wastewater treatment under visible light irradiation. The photocatalytic efficiency was evaluated on a basis of changes on concentration of total chromium (Cr) and total organic carbon (TOC). Kinetics and mass transfer were determined from change of flow rate and the hydraulic retention time of wastewater in photoreactor. The photocatalytic reduction of total Cr followed pseudo-first order model with variation of feed concentration. The optimum flow rate in total Cr removal was found at 750 mLmin-¹ with 1.20 mgL-¹min-¹ initial reaction rate and 0.0452 min-¹ kinetic rate constant. With the high flow rate (>750 mLmin¹); both overall rate constant and photocatalytic efficiency was decreased. In the testing of photostability of the N-doped TiO₂ thin film in fixed bed photoreactor, the slight decrease of photocatalytic activity in total Cr and TOC removal after 6 cycles of tannery wastewater treatment was in an acceptable range which suggested that the photocatalyst can be successfully reused in wastewater applications.