Improved water quality by process renewal in a pulp and paper mill

The Kaukas pulp and paper mill on southern Lake Saimaa was investigated to evaluate the environmental benefits of process renewal, i.e. the substitution of chlorine by chlorine dioxide in the bleaching and the modernisation of the biological effluent treatment. A comparative study of the mill effluent and the catchment water area was performed before (1991) and after (1993/1995) the changes. The chemical composition of the mill effluent was analysed with special emphasis on chlorinated organics and wood extractives. The same compounds were analysed in lake waters with respect to distribution and persistence. The study revealed a considerable decrease in the concentrations of chlorinated organics both in the mill discharge and in the lake. Most wood extractives also decreased in the effluent. However, the discharge of some wood extractives, such as sitosterol, was not significantly affected by the changes.