Selective removal of resin and fatty acids from mechanical pulp effluents by ozone

Fresh chemithermomechanical (CTMP) mill primary clarifier (combined) effluents were treated using a system capable of accurately applying small measured charges of ozone. It was shown that the efficiency of ozone transfer into effluent was much better than into water, and that there was no residual dissolved ozone. Small ozone charges destroyed high proportions of the total resin and fatty acids (RFAs) and juvabiones (JBs) present in the effluents. This effect diminished with increasing ozone charges. Likewise, effluent toxicity, as measured in the Microtox assay, decreased rapidly with the low ozone charges. The low charges of ozone were also shown to be effective in destroying both soluble and particulate RFAs. It was shown that there was a strong positive correlation between the RFA content and the acute toxicity of an effluent sample, and that all the acute toxicity was extractable with methyl-t-butyl ether. Both Microtox and Daphnia magna acute toxicity assays correlated with effluent RFA content, but the Microtox was somewhat more sensitive. Thus, ozone may be a useful economical treatment agent for selectively removing RFAs and toxicity from mill effluent streams.