Evaluation of ZnO, TiO2 and supported ZnO on the photoassisted remediation of black liquor, cellulose and textile mill effluents

Treatment of effluent from the cellulose and textile industries by applying a heterogeneous photocatalytic procedure using UV-light and free and supported catalysts is reported. When Kraft and textile effluents are submitted to UV-irradiation in the presence of free TiO2 and ZnO or silica gel supported ZnO, the colour fades progressively to reach substantial decolorization ratios. This decolorization process is accompanied by a considerable reduction of total phenol concentrations in the black liquor and final effluent. For bleaching mixture, the reduction of phenol concentration is not significant, and on the contrary, for textile effluents an increase of phenolic compound concentrations is observed during the initial phase of the photocatalytic process. The progressive degradation of the different chemical species contained in the effluents was demonstrated by HPLC analysis and total organic carbon contents determination. This degradation permitted an important reduction of the acute toxicity of the effluents.