The impact of paper additives on activated sludge

grantor: University of TorontoThe primary objective of this research was to identify paper additives with a potential to cause adverse effects on an activated sludge effluent treatment system, using a screening method based on batch respirometry. The screening of twenty different paper additives used at Abitibi-Consolidated's Iroquois Falls Mill revealed that three basic paper dyes (Orange 3, Violet 5, Red B) one cleaner/solvent and a microbiocide are the most toxic to the respiring biomass in the effluent treatment system. Polymeric additives, such as drainage and retention aids had no observable impact on the biomass. Although the oxygen uptake rate (OUR) of the biomass was decreased by up to 61% by Orange 3 paper dye, at ten times the worst expected dose (750 mg/L), significant inhibitions are not expected under normal operations in the paper mill. Qualitative microscopic examinations, showing toxicity to rotifers and protozoa, substantiated the screening results and in some cases revealed that subtle toxic effects which occur at low doses are not accompanied by an observable decrease in OUR. Continuous pilot plant testing confirmed the validity of the batch respirometric screening protocol. A seven day exposure to 200 mg/L of Orange 3 paper dye resulted in a 53% decrease of the specific oxygen uptake rate in the aeration basins, and the disappearance of all rotifers and protozoa. A complete recovery quickly followed the removal of paper dye from the treatment system feed. Removal of paper dyes by adsorption onto the biomass is believed to be an important toxicity removal mechanism.M.A.Sc