Date of Award


Semester of Degree


Document Type

Restricted Access Dissertation

Degree Name

Ph.D. in Environmental Resources Engineering


Environmental Resources Engineering

Major Professor

Wendong Tao

Steering Committee Member

Mark LeChevallier

Steering Committee Member

Lee Newman


Aeration accounts for approximately 50% of total energy used in the conventional activated sludge wastewater treatment process. Increasingly stringent wastewater discharge limits on nitrogen and higher costs of energy drive the search for new technologies and process control strategies that can be employed to treat wastewater with lower energy inputs while still producing high-quality effluent. The application of low dissolved oxygen simultaneous nitrification and denitrification operation in wastewater treatment plants for enhanced nitrogen removal is gaining popularity. The complexity of microbial ecology for biological nitrogen removal includes ammonia-oxidizing archaea, ammonia-oxidizing bacteria, complete ammonia oxidizers, nitrite-oxidizing bacteria, anaerobic ammonia oxidizing bacteria, and anaerobic and aerobic heterotrophic denitrifiers. Our current understanding of kinetics and microbial ecology cannot fully explain how total nitrogen is efficiently removed in biological nitrogen removal plants under low dissolved oxygen conditions. Therefore, it is necessary to study the mechanisms and associated processes for biological nitrogen removal using novel microorganisms to drive improvements for process optimization and energy savings. This study investigated the kinetics of biological nitrogen removal under low dissolved oxygen conditions, examined microbial communities and structure in the low dissolved oxygen process, and developed a process model and an aeration control strategy to achieve a stable low dissolved oxygen operation with reduced energy usage. The kinetic study found that microorganisms with high oxygen affinity were developed for nitrogen removal. The 16S rRNA gene amplicon sequencing results showed that Nitrospira were the only autotropic nitrifying bacteria discovered in five wastewater treatment plants while a diverse group of microorganisms were identified for simultaneous nitrification and denitrification in low dissolved oxygen operations. A feedback ammonia-based aeration control strategy remarkably reduced energy consumption without compromising treatment performance of a stable low dissolved oxygen operation. This study provided an understanding of microbial ecology and insights into process control and optimization for wastewater treatment plants operated under low dissolved oxygen simultaneous nitrification and denitrification conditions.