Current Status of the Pure Oxygen Activated Sludge Process in Canadian Mills, 2002 Environmental Conference Proceedings

M. G. Paice, T. Kovacs, J. Bergeron and B. O’Connor

Since 1980, more than one quarter of the activated sludge biotreatment systems installed in Canadian mills have been the pure oxygen enclosed type (UNOX/OASES). The choice of these designs was based in part on their compact footprint, and on claims of lower sludge production and ability to handle foul condensates. We have now reviewed the operating parameters and performance characteristics of these systems. They are operated over a surprisingly wide range of volumetric organic loadings and food to microorganism ratios. In spite of this, their performance with regard to meeting effluent regulations (BOD, TSS, and acute toxicity) has been as good as other activated sludge designs. One significant issue is the high concentrations of carbon dioxide commonly found in the treated effluent, which can cause acute toxicity to trout. Other issues unique to these designs are also reviewed.