Removal of 4-Chloro-3-Methylphenol (p-Chlorocresol) from Tannery Effluent, from Lab to Pilot Scale

This study determined the effectiveness of ozone and Fenton’s reagents, and the ozone delivery system, for the degradation of the persistent organic compound p-chlorocresol (4-chloro-3-methylphenol) in tannery wastewater. Laboratory trials demonstrated that removal of p-chlorocresol from wastewater at pH 4.1 using ozone was at least 70% within 2–3 h. Fenton’s reagent did improve the p-chlorocresol removal, but only by 10%. When we normalize the % removal data to account for reaction time and ozone dose, the degradation rates of p-chlorocresol in the ozone only and ozone plus Fenton’s treatments were similar, ~76 mg p-chlorocresol g⁻ O₃ h⁻¹. In the pilot trials, the addition of ozone via a venturi delivery system with improved circulation achieved up to 46% removal of the p-chlorocresol in wastewater at pH 4.1 within 24 h; this equated to a removal rate of 3.8 mg p-chlorocresol g⁻ O₃ h⁻¹. The large difference in removal rate between the pilot and lab trials was attributed to higher organic load in the wastewater. The addition of Fenton’s reagent increased the removal of the p-chlorocresol to 66% in the venturi injection trial and almost doubled the removal rate (6.7 mg chlorocresol g⁻ O₃ h⁻¹). The addition of ozone via a direct blower system was not as effective as the venturi system because of the large loss of ozone from the tank reactor.