Enhanced biological treatment of bleached kraft mill effluents - II. Reduction of mixed function oxygenase (MFO) induction in fish

Biological treatment studies with bleached kraft mill effluents (BKME) asse ssed the removal of hepatic MFO induction potency towards fish. Bench-scale activated sludge, facultative stabilization basin. and aerated stabilizati on basin processes were compared under conservative conditions of elevated sludge age and hydraulic retention times as well as moderate temperatures f or the treatment of bleachery effluents from a modernized bleached kraft mi ll using oxygen delignification and 60% chlorine dioxide substitution. Opti mized treatment for the removal of hard-to-degrade organics also consistent ly removed more than 85-90% of effluent-induced MFO activity of fish, based on laboratory bioassays. Follow-up mill-site pilot scale testing with an a ctivated sludge treatment process in extended-aeration mode also demonstrat ed >90% reductions in the MFO induction potential of whole mill effluent. C haracterization of various in-plant process waters sampled at the mill indi cated that the delignification and 60% aeration mode also demonstrated >90% reductions in the MFO induction potential of whole mill softwood-line blea ch plant was a major contributor (> 70 %) to the MFO induction untreated an d biologically-treated BKME. (C) 1999 Elsevier Science Ltd. All rights rese rved.