Integrated Ozonation‐Biotreatment of Pulp Bleaching Effluents Containing Chlorinated Phenolic Compounds

Abstract

Bleaching effluents from pulp and paper industry are problematic because they contain toxic chlorinated phenolic compounds and recalcitrant chlorinated lignin fragments of higher molecular weight. The chlorinated phenolic compounds have been shown to be rather easily removable in fluidized bed bioreactors. The total amount of adsorbable organic halogens (AOX), however, was only reduced by 20%‐30%. It is generally possible to oxidize all unsaturated organic compounds in the bleaching effluents by ozonation. However, ozone is still too expensive to allow complete treatment. Nevertheless, the increase of biodegradability of recalcitrant components by dechlorination and degradation of high molecular weight fractions by ozone can lead to increased efficiency in a subsequent biotreatment. In this study the simple ozonation of bleaching effluents with and without biological pretreatment was compared with sequential or cyclic ozonation—biotreatment schemes. By integrated ozonation—biotreatment, the degradation efficiency relative to the amount of ozone consumed was markedly increased. The overall efficiency of the treatment process in terms of fractional removals of global parameters COD, TOC, and AOX increased. More than 70% of AOX were eliminated. No toxic effect was observed in the cyclic reactor, where the liquid passed was cycling between an ozonation and a biotreatment zone. In the liquid phase no dissolved ozone could be detected in this reactor.