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Doctor of Philosophy


Chemical and Biochemical Engineering


Dr. Lars Rehmann

2nd Supervisor

Dr. Madhumita B. Ray



This thesis examined the use of commercially available Biolog 96-well plates containing different carbon sources for a microalgal bioassay. Quaternary ammonium compounds (QACs) were used as potentially toxic model compounds to demonstrate the applicability of the assay. Toxicity of dodecyl trimethyl ammonium chloride (DTAC) and didecyl dimethyl ammonium bromide (DDAB) on the growth of Scenedesmus obliquus varied significantly under autotrophic, heterotrophic and mixotrophic growth conditions. The concentration for 50% growth inhibition effect (EC50) of DTAC followed the order: autotrophic (0.48 ± 0.03 mg of DTAC/L) > heterotrophic (1.46 ± 0.04 mg of DTAC/L) > mixotrophic (2.11 ± 0.06 mg of DTAC/L), whereas for DDAB, the order of inhibition was different as: heterotrophic (0.52 ± 0.02 mg of DDAB/L) > autotrophic (1.18 ± 0.08 mg of DDAB/L) > mixotrophic (1.35 ± 0.02 mg of DDAB/L). Moreover, EC50 values were a function of carbon source and growth regime, showing that only EC­50 values do not fully capture the toxic effects of a potentially toxic compound might have on algal communities. Therefore, a new assay was developed based on community level physiological profiling (CLPP). Five different mixtures of artificially defined microalgal communities were employed and the changes in substrate utilization patterns by the treatment of hexadecyl trimethyl ammonium chloride (CTAC) were quantified using principal component analysis (PCA). The toxic effect of CTAC was significant (P < 0.05), showing 58% inhibition compared to the control and the effect was more pronounced for the treatment than that obtained by varying the initial composition of the defined algal communities. The newly developed assay was further applied on wetland water samples, wastewaters (i.e. primary and secondary), river water, and activated carbon treated and untreated oil sand process waters (OSPWs). The assay was able to generate a distinguishable response among these samples, measuring small differences within the respective water groups and larger differences between them.

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