Minimum Impact of a Kraft Pulp Mill: Assessment and Improvement of the Ecotoxicological Balance, 1996 International Pulp Bleaching Conference Proceedings

G. Lenon, G. Lombardo, B. Joseleau, J. C. Hostachy

In spite of an appreciable reduction of the amount of organochlorine compounds in bleached kraft pulp mill wastewaters, untreated effluents and some mill effluents, after biological treatment, exhibit acute toxicity and / or chronic toxicity to aquatic organisms. To reduce this toxicity, it is essential to situate its origin and its evolution in the process. Effluents were collected from the main pulp making steps and from the chemical recovery stage. Their toxicities were determined by the microtox bioassay for acute toxicity and by the algal growth inhibition test for chronic effects. Toxicity Emission Factors were calculated. and reported on a global balance sheet. Effluents showing the greatest acute toxicity were chosen in order to study the efficiency of an ozonation treatment in reducing toxicity. Amount of ozone, temperature and pH parameters were studied to define the optimal treatment conditions. Up to 90% of the initial acute toxicity was eliminated with a low ozone dose.