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UBC Theses and Dissertations

The effect of pH on microbial activity and community structure in the biological removal of resin acids from wastewater Werker, Alan Gideon


Pulp mills in Canada rely on biological treatment systems for the removal of resin acids that are released from wood during pulping and bleaching. These are priority contaminants for the pulping industry, since they have been frequently associated with events of toxicity breakthrough. Although, tighter mill control has helped to minimize the losses of resin acids in wastewater, acute toxicity removal in downstream biological treatment systems may still be insufficient, particularly under dynamic loading conditions. The mechanisms responsible for these limitations are not fully understood. This dissertation documents a fundamental study into the fate of resin acids during biological treatment. The objective was to quantify the influence of pH on the resin acid bioavailability, metabolism, and retention time during biological treatment. A progression of two batch and two continuous flow bioreactor investigations were undertaken to consider the interrelated issues of pH-dependent microbial activity and resin acid hydrophobicity. Changes in pH, within the typical range for biological treatment, significantly altered the bioavailability of resin acids and the community of microorganisms responsible for resin acid biodegradation. A sudden input of resin acids promoted an elevated level of community change during continuous treatment of bleached kraft mill effluent. The capacity of a treatment system to remove resin acids was found to be a function of the contaminant loading history. Time lag before biological removal in response to a shift-up in resin acid loading was significant and was also affected by the treatment system pH. Hence, the prevailing bioreactor pH operating condition, in conjunction with the period and amplitude of loading transients were shown to be key aspects controlling the microbial community structure and physiological state, which in turn determine the rate and extent of biological removal of resin acids. Through the course of the four investigations, novel contributions have been made in the areas of surface tension and microbial fatty acid measurements that have engineering application in future modelling and monitoring of the behaviour of microbial wastewater treatment processes.

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