Effects of ozone on resin acids in thermomechanical pulp and paper mill circulation waters

The present study investigated ozonation as means to remove resin acids from pulp and paper mill circulation waters. Ozone selectively oxidizes resin acids in debarking, thermomechanical pulping (TMP), and newsprint machine (PM) circulation waters. The relative ozone dose of 0.2 mgO(3)/initial mgCOD eliminated over 90% of total resin acid concentration in all tested waters, despite the initial resin acid or organic matter concentration. With that ozone dose, the removal of organic material (measured as COD) was only about 30%. Because of the different COD concentrations of tested waters, the absolute amount of ozone needed for over 90% resin acid reduction was 2000 mg/l for debarking water, 600 mg/l for TMP water, and 300 mg/l for PM water, when initial COD concentrations were 10,000, 3000, and 1500 mg/l, respectively. In theory, abictane type resin acids should be more susceptible to ozone attack than pimarane type resin acids, because of their conjugated double bond structure. In the experiments, a high oxidizability of pimarane type resin acids, as compared to abietane type resin acids, was found.