Environmental Engineering Program


First Advisor

Dr. Bruce Dvorak

Second Advisor

Dr.Ashraf Aly Hassan

Date of this Version



Mowat, K. (2021). Biofiltration Application at Ethanol Plants: Analysis of Aqueous Streams and Treatment of VOCs [University of Nebraska-Lincoln]. Civil and Environmental Engineering Theses, Dissertations, and Student Research.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Environmental Engineering, Under the Supervision of Professors Bruce Dvorak and Ashraf Aly Hassan. Lincoln, Nebraska: August, 2021

Copyright © 2021 Katie Marie Mowat (Donesky)


The United States used 14.5 billion gallons of the biofuel ethanol in 2019 produced primarily (82%) in dry-mill corn ethanol plants. These plants produce volatile organic compounds (VOCs) — some of which are hazardous air pollutants (HAPs) — during production. Traditional treatment methods for gaseous emissions use a large quantity of water or natural gas. Thus, a bio-trickling filter (BTF) is considered an innovative alternative treatment method. A lab-scale BTF was used in this study to look at the effect of ethanol concentration and temperature on the treatment of a HAPs mixture. Gaseous and aqueous testing were performed on the influent and effluent from the BTF. These tests were also completed on select aqueous streams from within two Nebraska ethanol plants (Plants A and B). This thesis concluded that a mesophilic (21ºC) BTF column had a higher removal efficiency for the mixtures tested than a thermophilic (60ºC) column due to pH and VOC solubility. As the concentration of ethanol increased the treatment of acetaldehyde decreased and ethanol removal increased by around 25-35%. This increase may be due to the microbial culture increasing its affinity to ethanol and/or an increase in internal mass transfer of ethanol. It was also found that the microbes had an affinity for VOCs in this order: formaldehyde, ethanol, acetaldehyde, and then methanol. From the aqueous sampling at the two ethanol plants, it was determined that neither of the plants had a stream that met the exact target C:N:P ratio of 200:4:1 that is necessary for use as a nutrient solution in a BTF. Many of the streams also contained chlorine or excess levels of ethanol— both of which are toxic to microbes. Therefore, the nutrient solution used will be either wastewater treatment plant (WWTP) effluent, a waste stream with nutrients added, or well water with nutrients added. Finally, this thesis concluded that in order for Plant B to meet the impurity limits as set by the federal drug administration (FDA) for ethanol plants transitioning into the production of alcohol-based disinfectants, the column tops or the final product process streams will need to be treated further.

Advisors: Bruce Dvorak and Ashraf Aly Hassan