During recent years the BOD-loading of pulp and paper mill wastewaters has decreased dramatically, due to more effective circulation of water in the processes, and the new activated sludge biological treatment plants. This traditional threat to the environment has been forgotten by the scientists who nowadays are more interested in the role of chlorine compounds discharged from bleaching processes. However, eutrophication due to nutrient loading is still present in many recipients of pulp and paper industry. The BOD-reduction has often been carried out on the cost of adding nutrients, pnosphorus and nitrogen to the purification processes. The biological treatment has also decreased the inhibitive effect of wastewater on the biological production of the recipient water body. Therefore, the eutrophication arises immediatly. The authors worry about the research of nutrients; loadings, development trends and eutrophication effects.

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