The Figure 1 shows the COD and TOC results obtained for the combined system (activated sludge-
O3/pH 8 and activated sludge-O3/pH 10). The O3/pH 10 ozonation process was more efficient,
achieving 54.4 and 48.7% for COD and TOC removal, respectively. The O3/pH 8.3, showed only 35.1
and 17.4% efficiency removal for these parameters. This indicates that the ozonation process at pH 10
was able to remove remaining refractory fraction, increasing the COD and TOC ratio removal. For the
removal of phenolic compounds the pH of the ozonation process seriously affected the efficiency of
the process. For the systems O3/pH 8.3 and O3/pH 10, the efficiency removal was 48.5 and 74%,
respectively after 60 minutes. At pH 10 deprotonation of phenol (pKa = 10) occurs and the ozone rate
constant increases by as much as six orders of magnitude [5]. The main advantage of the application of
ozone in the treatment of paper effluent was the color removal, with 76.9 and 88.5% reduction after 60
minutes for ozonation carried out at pH 8.3 and 10, respectively. Figure 2 shows the efficiency
removal for both parameters. It is possible observed that the treatment time can be reduced for 20
minutes without seriously affecting the efficiency of the ozonation process. It is an important result,
since this implies costs reductions.