Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Spring 2020 Physical and biological factors affecting oxygen transfer in the activated sludge wastewater treatment process Kenneth A. Campbell Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Environmental Engineering Commons Department: Civil, Architectural and Environmental Engineering Recommended Citation Campbell, Kenneth A., "Physical and biological factors affecting oxygen transfer in the activated sludge wastewater treatment process" (2020). Doctoral Dissertations. 2862. https://scholarsmine.mst.edu/doctoral_dissertations/2862 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. PHYSICAL AND BIOLOGICAL FACTORS AFFECTING OXYGEN TRANSFER IN THE ACTIVATED SLUDGE WASTEWATER TREATMENT PROCESS by KENNETH ASHBY CAMPBELL A DISSERTATION Presented to the Graduate Faculty of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in CIVIL ENGINEERING 2020 Approved by: Jianmin Wang, Advisor Glen Daigger Joel Burken Mark Fitch Melanie Mormile © 2020 Kenneth Ashby Campbell All Rights Reserved iii PUBLICATION DISSERTATION OPTION This dissertation consists of the following five articles, formatted in the style used by the Missouri University of Science and Technology: Paper I: Pages 70 – 100 were published in Water Environment Research. Paper II: Pages 101 – 138 were published in Chemosphere. Paper III: Pages 139 – 177 were published in Water Research. Paper IV: Pages 178 – 216 are intended for submission to Water Research. Paper V: Pages 217 – 262 are intended for submission to Chemical Engineering Journal. iv ABSTRACT The activated sludge (AS) process is widely utilized for wastewater treatment due to its versatility and general resiliency, but is energy intensive, requiring aeration and mixing energy inputs to maintain the biochemical reaction and optimize treatment performance. This study is focused on determining different factors that influence oxygen transfer and consequently its energy demand. AS morphology, as described by the d10, d20, d32, specific filament length (SFL), 30 min settleability (SV30), etc., does influence the OTE. Filamentous organisms increase the hydrodynamic radius of suspended particles, which dilates mixed liquor apparent viscosity (μapp) and impedes mass transfer. For example, an increase in the SFL 10 11 -1 from 3.8 x 10 to 2.7 x 10 μm g resulted in an increase of μapp in excess of 100% and decrease of OTE of 29%. The volumetric mass transfer coefficient (kLa) was most -1 0.85 significantly affected by the mixing intensity (P VR ) , superficial gas velocity (Usg) -0.75 and the μapp ,where the μapp is principally influenced by the SFL and ultimate settleability (SVULT), a new parameter based on regression analysis of times series settling data. The addition of surfactants to the influent wastewater increased OTE; however, greater dispersed growth resulted which mediated increases in the OTE, especially at higher feed concentrations. Complicating the issue of oxygen mass transfer in the AS process is the presence of floc and filamentous organism at the gas-liquid interface, which block the surface, restricting mass transfer. This effect tended to be more significant for short (10 d) SRT processes as compared to long (40 d) processes, yielding modified enhancement factors, E’A, of 0.59 to 0.78, respectively. v ACKNOWLEDGMENTS Principally, I would like to acknowledge Dr. Jianmin Wang, whose patient persistence and astute guidance were instrumental in my completion of this work. Dr. Wang’s enthusiasm and desire to have a fundamental understanding of processes was an inspiration and encouragement to me. Dr Glen Daigger has made himself readily accessible and has provided pertinent, direct feedback regarding my research. Thank you Drs. Melanie Mormile, Mark Fitch and Joel Burken for the hours of instruction and constructive assessments of my work both in the classroom and in the laboratory. Dr. Dimitri Feys of Missouri S&T donated his time and resources to aid in my understanding of fluid viscosity and its measurement. Dr. Cesar Mendoza of Missouri S&T and Dr. C.P. Huang of the University of Delaware provided helpful guidance regarding fluid viscosity. I must also acknowledge that this research would not be possible without the Center for Infrastructure Engineering Studies (CIES) research facilities. I would like to thank Brian Swift, Gary Abbott, Greg Leckrone and John Bullock for all the technical assistance provided throughout the course of my experimental regimen. Dr. Wenyan Liu and Ninu Madria provided much needed support in the laboratory operations. Jeff Medows provided a flexible work schedule that afforeded the ability to complete this extensive experimental regimen and finance life outside of the laboratory. Tuition remittance was provided by the Missouri University of Science and Technology through the Chancellor’s Fellowship program. vi TABLE OF CONTENTS Page PUBLICATION DISSERTATION OPTION ................................................................... iii ABSTRACT ....................................................................................................................... iv ACKNOWLEDGMENTS ...................................................................................................v LIST OF ILLUSTRATIONS ........................................................................................... xiii LIST OF TABLES ........................................................................................................... xvi NOMENCLATURE ....................................................................................................... xvii SECTION 1. INTRODUCTION ...................................................................................................... 1 1.1. OXYGEN TRANSFER AND UPTAKE IN THE ACTIVATED SLUDGE PROCESS ........................................................................................................... 4 1.1.1. Bubble Formation. .................................................................................... 6 1.1.2. Bubble Breakup and Coalescence. ......................................................... 13 1.1.3. Bubble Rise Velocity, Gas Holdup and Interfacial Area. ...................... 21 1.1.4. Oxygen Mass Transfer – Film Theory and Its Applications. ................. 24 1.1.5. Oxygen Mass Transfer – Penetration Model. ......................................... 28 1.1.6. Oxygen Uptake Rate. ............................................................................. 30 1.1.7. Oxygen Transfer – Design Approach. .................................................... 32 1.2. PHYSICAL FACTORS AFFECTING OXYGEN TRANSFER ..................... 40 1.2.1. Aerator Type........................................................................................... 40 1.2.2. Diffuser Configuration. .......................................................................... 45 1.2.3. Diffuser Fouling. .................................................................................... 46 vii 1.2.4. Mixing. ................................................................................................... 48 1.2.5. Surfactants. ............................................................................................. 53 1.3. BIOLOGICAL FACTORS AFFECTING OXYGEN TRANSFER ................. 61 1.3.1. Mixed Liquor Suspended Solids. ........................................................... 61 1.3.2. Solids Retention Time. ........................................................................... 63 1.3.3. Biological Floc Diameter. ...................................................................... 63 1.3.4. Extracellular Polymeric Substances. ...................................................... 65 1.4. CURRENT RESEARCH NEEDS .................................................................... 65 2. GOALS AND OBJECTIVES .................................................................................. 68 PAPER I. ACTIVATED SLUDGE MORPHOLOGY SIGNIFICANTLY IMPACTS OXYGEN TRANSFER AT THE AIR-LIQUID BOUNDARY ............................ 70 ABSTRACT ................................................................................................................. 70 1. INTRODUCTION .................................................................................................... 71 2. MATERIALS AND METHODS ............................................................................. 73 2.1. REACTOR SET UP.......................................................................................... 73 2.2. OXYGEN DEMAND AND TRANSFER EFFICIENCY DETERMINATION ......................................................................................... 76 2.3. VOLUMETRIC MASS TRANSFER COEFFICIENT DETERMINATION .. 77 2.4. VISCOSITY MEASUREMENT ...................................................................... 78 3. RESULTS & DISCUSSION .................................................................................... 79 3.1. REACTOR OPERATIONS .............................................................................. 79 3.2. SLUDGE SETTLEABILITY AND THE OTE ...............................................