Pulp and paper mills discharge large amounts of wastewater containing high concentrations of lignin, a coloring substance that is dangerous and presents high toxicity to the environment. In this study, ozonation in alkaline ambience was evaluated for color reduction in black liquor, generated in a cotton linter mill. It was observed that the ozonation time to reach 80% color reduction was higher at a lower initial ozone dose (0,4 gO3 L-1 h-1) in comparison to a higher initial ozone dose (4,3 gO3 L-1 h-1). On the other hand, the amount of consumed oxidant was lower at the lower ozone dose. It is suggested that molecular oxygen participates in the oxidation mechanism of colored compounds, which is initiated by hydroxyl radicals (•OH) formed during ozonation in alkaline ambience.
ozonation; AOP; black liquor; color
