Contribution of Non-Biological Mechanisms to AOX Reduction Attained in Anaerobic Treatment of Bleached Kraft Effluents, 1994 Environmental Conference Proceedings

J. Dorica and A. Elliot

Laboratory anaerobic and aerobic reactors treating kraft bleach plant effluent were operated continuously for approximately one year to determine AOX removal efficiencies and the contribution of non-biological mechanisms to the overall AOX removal process.

BOD removal in the anaerobic stages varied between 31% and 53%, with the hardwood effluent responding slightly better to the treatment. Similarly, the AOX removal from the hardwood effluents was higher (65% and 71%, for single stage and two-stage treatment, respectively) than that for softwood effluents (34% and 40%). Chlorate was removed easily from both softwood and hardwood effluents (99% and 96%, respectively), with little difference in efficiency between the single-stage and two-stage anaerobic systems. Biogas yield decreased with increasing BOD load for both the softwood and hardwood effluents.

Anaerobic plus aerobic treatment removed in excess of 92% of BOD chlorate. AOX removal was 72% to 78% with hardwood effluents and 35% to 43% with softwood effluents. Most of the AOX was found to be removed from hardwood effluents during feed preparation and storage. Control treatment tests in non-biological reactors confirmed the presence of chemical mechanisms during the treatment of hardwood effluents at 55 degrees Celsius. The AOX removal that could be attributed to the anaerobic biomass ranged between 0 to 12%.