Activated Sludge Treatment of Kraft Mill Effluents from Conventional and Oxygen Bleaching

Conventional and oxygen bleaching effluents from hardwood kraft pulp mills were treated in laboratory-scale activated sludge processes. The main interest was the fate of organochlorine compounds in the activated sludge process.

In the treatment of conventional bleaching wastewaters the BOD₇-reduction was 80-91 % and in oxygen bleaching wastewaters 86-93 %. The respective COD_Cr removals were about 40 % and about 50 %.

The AOX reductions were on average 22 % and 40 % in the treatment of conventional and oxygen bleaching effluents, respectively. The reductions of chlorinated phenols, guajacols and catecols were usually more than 50 % in both reactors. Very little accumulation of AOX into the sludge was observed. The stripping of AOX from aeration unit was insignificant.