Treatment of Direct Red 23 in recirculating semi-pilot system by O3/UV process: Operational parameters effect and central composite design modeling

The treatment of C.I. Direct Red 23 (DR23) solution has been investigated by the ozonation under UV irradiation (O3/UV) in a recirculating semi-pilot mode. Decolorization efficiency (DE%) of DR23 was compared using the O3 and O3/UV processes, which was74.9% and 92.7% after 30-min treatment of the dye (100 mg/dm3), respectively. Then, the effect of experimental parameters on the O3/UV process including initial dye concentration, ozone mass flow rate and initial pH was studied. The obtained results revealed that the decolorization efficiency increased by enhancement of ozone amount and decreasing of the DR23 concentration; the decolorization process was performed efficiently at the basic condition (pH= 10) due to the production of extra hydroxyl radicals. The pseudo-first order kinetic was observed for the dye decolorization. Electrical energy per order decreases using the O3/UV process at the desired pH 10 indicating adequate synergistic effect of the photolysis and ozonation. Eventually, central composite design (CCD) approach was properly applied for prediction of the DE% with appropriate performance (R2 = 98.52%) and optimization of the process.