Understanding the role of activated sludge in oxygen transfer to improve wastewater treatment sustainability

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Wastewater treatment plants play a critical role in environmental protection. In the United States, municipal wastewater treatment plants (WWTPs) process billions of gallons of wastewater every day to remove suspended solids, organic matter, and excess nutrients including nitrogen and phosphorus. Aeration is a critical unit operation in municipal WWTPs as it provides the required oxygen for the activated sludge process used in aerobic biological wastewater treatment to remove organic matter and nutrients. However, aeration requires a significant amount of energy and accounts for 70-80 % of the total energy used in an activated sludge wastewater treatment process. The overarching goal of this project is to advance the development of innovative solutions to reduce the aeration energy required to operate an activated sludge wastewater treatment process. To advance this goal, the Principal Investigator proposes to carry out an integrated experimental and modeling program to characterize and unravel the physicochemical and biological processes and parameters that control oxygen transfer in the mixed liquor of an activated sludge bioreactor. The successful completion of this project will benefit society through the generation of new fundamental knowledge and innovative solutions that could reduce the energy consumption and greenhouse gas (GHG) emissions of municipal WWTs. Additional benefits to society will be achieved through outreach and educational activities including the mentoring of two graduate students at the Missouri University of Science and Technology.In aerobic biological wastewater treatment, aeration accounts for approximately 50% of the total process energy consumption. Preliminary research by the Principal Investigator (PI) of this project has established that the biological and physicochemical properties of activated sludge have a significant impact on oxygen transfer during aeration. Building upon the results of this preliminary work, the PI and his research team propose to carry out an in-depth investigation of the oxygen transfer process in the mixed liquor of an activated sludge bioreactor including at the gas-liquid, liquid-solid, and gas-liquid-solid interfaces. The specific objectives of the research are to: 1) Evaluate the effects of sludge physical properties (e.g., morphology, settleability, viscosity, and hydrophobicity) on oxygen transfer at the gas-liquid interface; 2) Assess the effects of the sludge physical properties (listed above) and sludge biological parameters (e.g., microorganism population and concentration of extracellular polymeric substances) on oxygen transfer at the liquid-microorganism interface; 3) Evaluate the mechanisms of enhancement of oxygen transfer by microorganisms at the air-liquid interface; and 4) Develop and validate dimensionless process parameters that could be used to characterize the intrinsic oxygen transfer property of the mixed liquor of an activated sludge bioreactor. The successful completion of this project has the potential for transformative impact through the generation of fundamental knowledge and process design tools that could be leveraged to reduce the energy required to aerate and operate an activated sludge wastewater process. To implement the education and outreach activities of the project, the PI plans to leverage the Opportunities for Undergraduate Research Experiences program at the Missouri University of Science and Technology to provide research training opportunities to two undergraduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.