Origin of Effluent Toxicity from a Simulated BCTMP Process, 1993 Environmental Conference Proceedings

Untreated effluents from bleached chemithermomechanical pulp (BCTMP) mills exhibit ahigh toxicity to aquatic organisms. This study considers where the aquatic toxicity originates during radiata pine BCTMP pulp manufacture and the chemical components that contribute to this toxicity.

Effluents from the manufacture of radiata pine CTMP in a pilot plant and from laboratory simulation of chip and pulp washing and peroxide bleaching were collected and their toxicity determined by Microtox. Microtox EC50 values for the effluents were between 0.012 and 21.5% v/v. Effluent produced from the plug screw feeder before sulfite impregnation and before refining was found to be most toxic. Based on toxicity emission factors, the effluents from the plug screw feeder before chip impregnation and before refining, and bleaching effluent contributed most to the overall acute toxicity. In agreement with overseas results, resin acids appeared to be a significant contributor to the acute aquatic toxicity of radiata pine BCTMP pulp mill effluents. However, other components in the effluents may contribute to the toxicity, particularly chronic sublethal effects.