Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Civil, Construction, and Environmental Engineering

First Advisor

Timothy G. Ellis

Second Advisor

Hans van Leeuwen


Food processing industries typically produce large quantities of high strength organic wastewater. The standard approach for such wastewater would be anaerobic pretreatment. However, the wastewater from the Quaker Oats Company located in Cedar Rapids, Iowa USA contained furfural, which was found to be toxic to anaerobic microorganisms.;In this study, batch and continuous laboratory scale experiments were performed to investigate the treatment of furfural-based wastewater using aerobic yeast. Three yeasts, Candida guillermondii, C. tropicalis , and C. utilis, were first studied in batch tests. All yeast cultures could lower the COD in the wastewater by more than 90%.;As the work was done under non-aseptic conditions, bacterial growth also occurred. Much of the work focused on finding operational conditions to minimize bacterial growth. At a pH of 4.5, the maximum specific growth rate, mu max, of C. utilis and bacteria were 0.13 h-1 and 0.03 h-1 and the value of half-saturation coefficient for substrate, Ks, were 160 mg COD/L and 12 mg COD/L, respectively. Accordingly, when substrate concentrations were higher than 30 mg COD/L, yeast grew faster than bacteria.;Yeast cultivation in continuously stirred aerobic reactors was studied with different yeast cultures. The effect of the age of the yeast or solids retention time (SRT) on reactor performance was investigated initially. SRT values of 1.0, 1.3, 1.5, 1.75, and 2 days were investigated and the reactors were controlled at a constant pH of 4.5 and temperature of 35°C. C. tropicalis and C. utilis and mixed cultures of these two yeast were used. The results showed that an SRT of 1.5 days was optimal to treat wastewater, maintain the yeast culture, and minimize bacterial contamination. All three yeast cultures could remove COD from the wastewater up to 90% at this SRT.;Subsequently, the effect of temperature on yeast performance was studied. C. tropicalis and C. utilis were studied in separate reactors. Two reactors were run at temperatures of 25, 30, 35, and 40°C. The SRT and pH were controlled at 1.5 day of 4.0 respectively. The results indicated that the optimum operating temperature in terms of removal efficiency, yeast biomass yield, and prevention of bacterial contamination was 30°C. Under these conditions, both C. tropicalis and C. utilis could remove COD by 90%.;Finally, the effect of pH on yeast performance was investigated. C. tropicalis and C. utilis were studied in separate reactors. The reactors were operated at different pH values, i.e. 3.0, 3.5, 4.0, 4.5, 5.0, and 5.5. The SRT and temperature of 30°C were controlled at 1.5 days and 30°C respectively. The higher pH increased the removal efficiency. Bacterial contamination was significant at pH values of 5.0 and 5.5. Therefore, the optimum pH range in terms of treatment efficiency, yeast biomass yield, and preventing bacterial contamination was between 4.0 and 4.5. At this pH range, more than 90% COD removal was accomplished in both reactors.



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Monchai Wongkarnka



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102 pages