Design of Small Scale Anaerobic Digesters for Application in Rural Developing Countries

125 Pages·2015·2.17 MB·English

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Graduate Theses and Dissertations Graduate School
2011
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Laurel Erika Rowse
University of South Florida, [email protected]
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Design of Small Scale Anaerobic Digesters for Application in Rural Developing

Countries

by

Laurel E. Rowse

A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science
Department of Civil and Environmental Engineering
College of Engineering
University of South Florida

Co-Major Professor: Sarina J. Ergas, Ph.D.
Co-Major Professor: James R. Mihelcic, Ph.D.
Daniel H. Yeh, Ph.D.

Date of Approval:
November 2, 2011

Keywords: Biogas, Manure Treatment, Methane Cooking Fuel, Particulate Matter Indoor
Air Pollution, Biodigester

Copyright © 2011 Laurel E. Rowse
Dedication

To Paul J. Notarianni – An amazing, courageous person and a great friend. One
day, I will build a space ship powered by liquid methane produced from animal waste.
To Casey, Eleni, and Daragh – Admirable women of strength speaking truth.
To Kate – Whom I never knew. May we bring change to the Peace Corps in her
memory and name.
Acknowledgments
Many people helped me in the course of researching and writing this document.
Professor Sarina Ergas was extremely helpful and supportive, always ready to answer
questions, offer insights and suggestions, and inspire me to do more than I ever thought
was possible. Professor Jim Mihelcic was extremely supportive to me, helped me narrow
down my research interests, and provided a broader perspective of the research our group
is doing in developing countries. Professor Daniel Yeh was always willing and eager to
provide opportunities for learning outside the classroom. He made possible the
opportunity for me to spend a summer as an International Research Experience for
Students Scholar doing research at the UNESCO IHE laboratory in Delft, the
Netherlands. I am grateful to my parents, Dianne Rowse and Nick Rowse, for their love
and support. Thank you to my sister, Linnea Rowse. Thank you, Tommy Lynn, James
Buckingham, and Matt Verbyla. Thank you to my family, friends, and fellow
environmental engineering students. I acknowledge the financial support provided to me
by the Master's International Program in Civil & Environmental Engineering at the
University of South Florida. Additionally, this material is based upon work supported by
the National Science Foundation1.

1 NSF funding is under the Scholarships in Science, Technology, Engineering, and Mathematics (S-STEM,
Grant No. 0965743). Any opinions, findings, and conclusions or recommendations expressed in this
material are those of the author and do not necessarily reflect the views of the National Science Foundation.
Table of Contents

List of Tables ..................................................................................................................... iv

List of Figures ......................................................................................................................v

List of Symbols .................................................................................................................. vi

List of Acronyms ............................................................................................................. viii

Abstract ................................................................................................................................x

Chapter 1: Introduction ........................................................................................................1
1.1 Problem Description ..........................................................................................1
1.2 Introduction to Anaerobic Digestion .................................................................2
1.3 Positive Community Impacts of Anaerobic Digestion ......................................3
1.3.1 Indoor Air Pollution ............................................................................6
1.3.2 Energy Production and an Alternative Cooking Fuel: Methane .........8
1.3.3 Addresses Unsustainable Deforestation Caused by Wood Fuel
Use ......................................................................................................8
1.3.4 The Empowerment of Women ............................................................9
1.3.5 Treatment of Animal and Human Waste ..........................................10
1.3.6 Anaerobic Digestion Generates Less Biosolids for Disposal ...........11
1.3.7 Nutrient - Rich Effluent as a Fertilizer .............................................12
1.3.8 Mitigation of Methane and Carbon Black Released into the
Atmosphere .......................................................................................13
1.4 Disadvantages of Anaerobic Digestion ............................................................14
1.5 Summary of Potential for Anaerobic Digesters for Application in Rural
Developing Countries ......................................................................................16
1.6 Objectives ........................................................................................................17
1.7 Scope of Work .................................................................................................17

Chapter 2: Literature Review .............................................................................................19
2.1 Microbiology of Anaerobic Digestion .............................................................19
2.2 Simple Reactor Technologies ..........................................................................22
2.2.1 Batch Reactor ....................................................................................24
2.2.2 Continuous Stirred Tank Reactor (CSTR) ........................................25
2.2.3 Plug Flow Reactor (PFR) ..................................................................26
2.3 Operational Configurations of Reactors ..........................................................26
2.3.1 Recycle ..............................................................................................26
i
2.3.2 Reactors in Series ..............................................................................27
2.3.3 Two-Stage Anaerobic Digestion .......................................................27
2.3.4 Phased Anaerobic Digestion .............................................................28
2.3.5 Reactors in Parallel ...........................................................................28
2.3.6 Semi – Batch .....................................................................................29
2.4 Reactor Designs Currently in Use for Small Scale Anaerobic Digestion in
Developing Countries ......................................................................................30
2.4.1 Fixed Dome Anaerobic Digester ......................................................32
2.4.2 Floating Drum Anaerobic Digester ...................................................35
2.4.3 Polyethylene Tubular Anaerobic Digester ........................................37
2.5 Organic Substrates ...........................................................................................39
2.6 Factors Affecting Performance ........................................................................42
2.6.1 Hydraulic Retention Time (HRT) .....................................................42
2.6.2 Solids Retention Time (SRT)............................................................43
2.6.3 Organic Loading Rate .......................................................................44
2.6.4 Safety Factor .....................................................................................45
2.6.5 Mixing ..............................................................................................46
2.6.6 pH ......................................................................................................47
2.6.7 Alkalinity ..........................................................................................48
2.6.8 Temperature ......................................................................................49
2.6.9 Volatile Solids Reduction .................................................................49
2.6.10 Gas Production ................................................................................50
2.7 Monitoring Parameters.....................................................................................50
2.8 Pathogen Reduction .........................................................................................55
2.9 Social Components of Development Projects..................................................56
2.10 Operation of an Anaerobic Digester Project ..................................................62

Chapter 3: Design Tool Development for Sizing the Bioreactor and Gas Storage Unit ...63
3.1 Model Inputs ....................................................................................................63
3.2 Model Calculations ..........................................................................................65
3.2.1 CHON Formula of Influent Waste Stream .......................................66
3.2.2 Stoichiometric Coefficients and Overall R Equation........................68
3.2.3 Amount of Biogas Produced per Day ...............................................70
3.2.4 Percent Methane................................................................................73
3.2.5 Volume of Water Fed per Day and Total Volume of Digester .........73
3.2.6 Digester Dimensions .........................................................................76
3.2.7 Rate Kinetics and SRT ......................................................................78
3.3 Model Outputs .................................................................................................81

Chapter 4: Results and Discussion .....................................................................................82
4.1 Case Study 1: Family – Sized Anaerobic Digester ..........................................82
4.2 Case Study 2: Anaerobic Digester for Six Households ...................................85
4.3 Case Study 3: Village – Sized Anaerobic Digester .........................................87
4.4 Discussion ........................................................................................................89
4.5 Recommendation for Guidelines for Residuals Disposal ................................90

ii
Chapter 5: Conclusions and Recommendations ................................................................91
5.1 Conclusions ......................................................................................................91
5.2 Future Work .....................................................................................................93

References ..........................................................................................................................95

Appendices .......................................................................................................................100
Appendix A: Calculation of Organic Loading Rates ...........................................101
Appendix B: Design Tool Excel Spreadsheet ......................................................102

About the Author ................................................................................................... End Page

iii
List of Tables

Table 1.1 Benefits of Anaerobic Digestion in Developing Countries .................................4
Table 2.1 Characteristics of Agricultural Substrates Used to Calculate C H O N
n a b c
Formulas ............................................................................................................41
Table 2.2 Suggested Operation Parameters for Rural Developing World
Applications .......................................................................................................42
Table 2.3 Monitoring Tests for Anaerobic Digestion Field Studies ..................................51
Table 3.1 User Inputs into the Model ................................................................................65
Table 3.2 Model Assumptions ...........................................................................................80
Table 3.3 Model Outputs ...................................................................................................81
Table 4.1 Inputs for Case Study 1: Family – Sized Anaerobic Digester ...........................84
Table 4.2 Outputs for Case Study 1: Family – Sized Anaerobic Digester ........................84
Table 4.3 Inputs for Case Study 2: Anaerobic Digester for Six Households ....................86
Table 4.4 Outputs for Case Study 2: Anaerobic Digester for Six Households ..................86
Table 4.5 Inputs for Case Study 3: Village Sized Anaerobic Digester ..............................88
Table 4.6 Outputs for Case Study 3: Village Sized Anaerobic Digester ...........................88
Table B.1 User Input Interface for the Excel Spreadsheet Design Tool ..........................102
Table B.2 Mass Balance Piece of the Model ...................................................................103
Table B.3 Semi-Empirical Kinetic Model Piece of the Model ........................................105
iv
List of Figures

Figure 2.1 Anaerobic Digestion Process Diagram .............................................................21
Figure 2.2 Simple Reactor Designs for Rural Developing Country Applications .............23
Figure 2.3 Stratification in a Standard – Rate Anaerobic Digester ....................................25
Figure 2.4 Semi – Batch Operation of a Reactor is a Combination Between
Continuous Flow Operation and Batch Operation ...........................................29
Figure 2.5 Fixed Dome Anaerobic Digester ......................................................................34
Figure 2.6 Floating Drum Anaerobic Digester ..................................................................36
Figure 2.7 Polyethylene Tubular Anaerobic Digester .......................................................38
Figure 3.1 Anaerobic Digester Design Tool Flowchart .....................................................64
Figure 3.2 Conceptualization of the Volume of Water Added as Water, the Volume of
Water Added as Moisture in Manure, and the Volume of Solids Added as
Solids in Manure ..............................................................................................79

v
List of Symbols
a = animal
kg = kilogram
m = meter
d = day
% = percent
Q = volumetric flow rate (m3/d)
Q = initial volumetric flow rate (m3/d)
0
C = concentration
C = initial concentration
0
kg VS = kilograms of volatile solids
μg = microgram
μm = micron; micrometer
L = liter
mg = milligram
mol = mole
θ = solids retention time (d)
c
X = cell concentration
Q = volumetric flow rate, out (m3/d)
w
X = cell concentration, out
w
C = concentration of volatile solids (kg VS/m3)
VS
vi