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A respirometric investigation of the activated sludge treatment of BKME during steady state and transient operating conditions

University of British Columbia

Activated sludge is commonly used to treat bleached kraft pulp mill effluent (BKME). Treatment performance during steady state operation is acceptable, but may be less than adequate during periods of unsteady state operation, such as process spills or temperature changes. Nineteen batches of BKME were treated in two lab scale activated sludge bioreactors. The effects of the solids retention time (SRT) and the presence of an aerobic selector on the activated sludge treatment of BKME during steady state and transient operating conditions were investigated. Respirometric methods for the study of activated sludge kinetics were investigated in detail, including the unsteady state nature of the assay, and the presence of multiple substrates. BKME is composed of many different substrates, and the composition was found to be variable from batch to batch. The substrate fractions were classified into two main groups, the readily biodegradable (70%) and the slowly biodegradable (30%). The removal rates of the readily biodegradable substrates were approximately an order of magnitude greater than the removal rates of the slowly biodegradable substrates. The substrate removal rates and the stoichiometry were more dependent upon the wastewater characteristics than the solids retention time or the presence of an aerobic selector. The pH affects the removal rates of all of the substrates in B K M E approximately to the same extent. Below pH 6 and above pH 9, the metabolic activity of the activated sludge was low enough to result in incomplete removal of the slowly biodegradable substrates. Outside of the pH range 5.5 to 9.5, the decay rate of the bacteria increased. Operating at a high SRT (fifteen days) mitigated the negative impact of pH on the biomass.

Thesis/Dissertation

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2009-06-29

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http://hdl.handle.net/2429/9831

Chemical and Biological Engineering

University of British Columbia

UBCV

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