Removal of colour and COD from paper and pulp industry wastewater by ozone and combined ozone/UV process

Abstract

ABSTRACT This study aims to investigate the effectiveness of ozonation alone and combined ozone/UV process for the removal of colour and chemical oxygen demand (COD) of black liquor discharged from paper and pulp industry. Moreover, the effect of several reaction parameters such as initial pH, ozone dose and reaction time were studied. Finally, pseudo-first-order considerations were applied to determine the rate of reactions in both ozonation alone and ozonation combined with UV process. The results indicate that COD and colour removal were enhanced by increasing the solution pH. The highest COD reduction and decolourization efficiencies were 56% and 71% at pH 9.8 with the O 3 /UV process with ozone dose of 0.2 mg/mL. The comparative study of both ozonation and UV-Ozone processes indicate that UV-ozone process was found to be more effective as compared with ozonation alone. COD and colour removal of pulp and paper wastewater organic load follows the pseudo-first-order apparent reaction kinetics. The fastest rate constant (4.40 × 10 –3 /min) at alkaline pH of wastewater was observed with O 3 /UV processes. Therefore, it was concluded that O 3 /UV process showed better performance than O 3 alone for the removal of colour and COD in paper and pulp wastewater near wastewater pH.