Performance of photo-catalytic oxidation for degradation of chlorophenols: Optimization of reaction parameters and quantification of transformed oxidized products.

In a pulp and paper mill, chlorine bleaching of pulp generates toxic aqueous stream containing various chlorophenols (CPs) which are not removed easily by biological process. The objective of the study was to optimize photo-catalytic oxidation reaction for synthetic wastewater containing mixture of mono-, di-, tri- and penta-CPs (i.e., 4-CP; 2,4-DCP; 2,4,6-TCP, and PCP) and evaluate its performance for simulated bleaching effluents produced during pulp bleaching stages. The experimental runs were performed in a glass reactor (capacity = 500 ml) with UV lamp (200-390 nm). A maximum TOC reduction of 93% was achieved for synthetic wastewater (initial TOC = 42 mg/L) at the following conditions: pH = 4.4 (unadjusted), H2 O2 dose = 6.8 mM (stoichiometric), [H2 O2 ]:[Fe2+ ] = 65 and run time = 37 min. Under these conditions, ∼90% of the chlorine atoms were dissolved as chloride ions in the treated wastewater. High performance liquid chromatography analysis on liquid samples extracted during the oxidation reaction revealed no accumulation of carboxylic acids in treated wastewater. At similar operating conditions, TOC removal from simulated bleaching effluent was 78% during photo-catalytic process compared to ∼50% obtained after Fenton's oxidation.