Ozone Removal of Fluorescent Whitening Agents (FWA's) From Pulp, 1997 Pulping Conference Proceedings

In order to use secondary fibers in food packaging board, we have to meet special requirements set by the FDA. Among many contaminants encountered with waste paper, fluorescent whitening agents (FWA’s) or optical brighteners are sometimes used to improve the appearance of paper products, and thus will enter the recycling plant. In the present study, removal of FWA’s from pulp was examined. Effects of operational variables such as consistency, pH and ozone charge on the process efficiency were investigated. Results showed that all three parameters, pH, consistency and ozone charge, had significant impacts. The highest efficiency was achieved at a high consistency range (25%). Even though the pH role was that the lower the pH the more optical brighteners removed, a high pH treatment at high consistency still removed more FWA’s than a low pH but low consistency process. As ozone charge increased in the range studied, the amount of optical brightener increased linearly. This study also covered the change in pulp physical properties but only pH was found to have some impact under certain conditions. If ozone treatment was at high consistency, not only more FWA’s were removed but pulp strength properties were not sensitive to pH and ozone charge. It seemed that ozone reacted preferentially with fluorescent molecules.