Denitrification of a Pulp Mill Effluent Waste Water Treatment at Port Alice, 1997 Environmental Conference Proceedings

With the introduction of more stringent effluent discharge standards by both federal and provincial governments during 1995, many Canadian pulp and paper mills had to upgrade their waste water treatment systems. One such was Port Alice, part of Western Pulp Inc. It is an ammonia-based sulphite mill, located in British Columbia, producing high purity dissolving pulp grades. As well as reductions in permitted AOX and BOD concentrations, contaminant fees for the discharge of other permitted substances were to be increased and the range of substances so controlled extended. Toxicity provisions required that the discharge of ammonia nitrogen be carefully controlled. To reach the per-mitted AOX discharge maximum of 1.0 kg/ton pulp, the bleach plant was rebuilt to allow the elimination of chlorine, by substitution with chlorine dioxide. Most of the pulp produced is ECF pulp. Extensive pilot plant tests of Port Alice waste waters had shown that it was possible to treat condensate anaerobically, but that the introduction of bleach plant effluent caused significant reductions in BOD removal efficiency. In view of the difficult start-ups of some of the anaerobic installations in North America, and the lack of a lengthy operating record, it was decided that a conventional air-activated sludge system would be installed. However, high concentrations of ammonia and nitrates would have resulted in high costs, due to the contaminant fees on both of these, and possibly poor results in test bioassays. Ammonia discharged averaged 12 tons/day with a 90 th percentile of 14 tons/day. After allowing for incorporation into biomass, the surplus ammonia was estimated to average 8.5 tons/day. Consequently, it was decided to design a system to operate with a high sludge age to allow ammonia conversion to nitrate, and to incorporate an anoxic zone into the treatment...