Photocatalytic oxidation of elemental chlorine free bleaching effluent with UV/TiO2

Photocatalytic oxidation of ECF (Elemental Chlorine Free) bleaching effluent (D-1 and E stage effluents of D1ED2 and OD1ED2 bleaching sequences) with UV/TiO2 treatment process has been studied for environmental load reduction. The effluents were generated in the laboratory by chlorine dioxide bleaching and alkaline extraction of the mixed hardwood kraft pulp under controlled conditions. Photodegradation of the effluents was done under UV radiation with 0.5 g/L of TiO2 at a pH 7.0 for 4 hrs in a slurry type reactor. Higher removal efficiencies have been observed with OD1ED2 than D1ED2 sequence. UV/TiO2 oxidation removed 46.3% BOD (Biochemical Oxygen Demand), 64.2% COD (Chemical Oxygen Demand), 88.3% color, and 59.3% AOX (Adsorbable Organic Halides) for Di and 55% BOD, 66.5% COD, 86.7% color, and 64.2% AOX for E stage effluents of OD1ED2 sequence. A significant improvement in biodegradability index (BOD/COD ratio) has also been observed for OD1ED2 than D1ED2 sequence, the values being 0.08 and 0.14 for Di, 0.09 and 0.1 for E stage effluents of D1ED2 and OD1ED2 sequences. This shows that effluents from OD1ED2 sequence are more amenable to photocatalytic degradation.