Genotoxic effects of kraft pulp mill effluents treated by biological aerobic systems

Kraft mills are responsible for massive discharges of highly polluted effluents containing high COD concentration, and also exert toxicity on aquatic organisms. This toxic effect is generally related to the presence of abietic acid and sterols. The present work focuses on the search of a possible correlation between the presence of these compounds and the toxic effect of both untreated and treated bleached kraft mill effluents (BKME). An activated sludge system and an aerated lagoon, fed with BKME, were operated at organic loading rates (OLR) of 0.20, 0.40 and 0.60g COD/L day, and the genotoxicity of both untreated and treated BKME was evaluated using the Bacillus subtilis 'rec' assay. The results indicate that toxicity of BKME could not be explained by the presence of abietic acid and sterols. Moreover, only a partial removal of the chronic toxicity could be achieved by the biological system used.