MS Thesis Defense


Molly Hite
Master's Student, Water Resources Science

June 8, 2018


Quantification of Nitrifying Bacterial Populations in Three Biological Wastewater Treatment Plants Throughout Seasonal and Process Variations in Minnesota

Biological wastewater treatment plants aim to remove nutrients from raw wastewater to protect effluent-receiving bodies of water and comply with state and federal discharge regulations. Ammonia is a pollutant of concern that is targeted for removal and the microbes responsible, or “nitrifiers”, consist of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). Identification and quantification of nitrifiers is of interest to wastewater treatment plant operators due to the large energy demand exerted by nitrification. Nitrifiers require oxygen for the oxidation of ammonia to a less toxic compound, nitrate. The aeration required to meet the oxygen demand of nitrification is a major cost associated with wastewater treatment. During the winter months in Minnesota, ammonia regulations are relaxed and the dissolved oxygen (DO) supply can be decreased. However, reestablishing nitrification activity by increasing DO in the early spring is crucial to prevent future permit violations. Determining the extent to which DO concentration and/or temperature play in nitrifier abundance was a major goal of this research project. Through quantitative polymerase chain reaction and Illumina sequencing, AOB and NOB were successfully quantified in three Minnesota wastewater treatment plants throughout a year-long sampling period. It was discovered that temperature and DO did not statistically and reliably impact AOB or NOB abundance, but a decrease in DO did affect NOB abundance.