identifying cost savings through energy conservation measures in mechanically aerated activated ...

287 Pages·2012·9.18 MB·English

IDENTIFYING COST SAVINGS THROUGH ENERGY CONSERVATION MEASURES IN
MECHANICALLY AERATED ACTIVATED SLUDGE TREATMENT PROCESSES IN SOUTHEAST
FLORIDA
by
Eric Stanley

A Thesis Submitted to the Faculty of
The College of Engineering and Computer Science
in Partial Fulfillment of the Requirements for the Degree of
Master of Science

Florida Atlantic University
Boca Raton, FL
May 2012
IDENTIFYINGCOSTSAVINGS THROUGHENERGYCONSERVATIONl\ffiASURES IN
l\ffiCHANICALLYAERATED ACTIVATEDSLUDGE TREATMENTPROCESSESINSOUTHEAST
FLORIDA
By
Eric Stanley
This thesis was prepared under the direction of the candidate's thesis advisor, Dr. Frederick Bloetscher,
Departmentof Civil, Environmental, and Geomatics Engineering" and.has been approved by the members
of his supervisory committee. It was submitted to the faculty of theCollege ofEngineering andComputer
Science and was accepted inpartial fulfillmentoftherequirementsforthedegree ofMaster ofScience.
SUPERVISORYCOMMITTEE:
eoerickBloetscher,Ph.D.,P.E.
Thesis Advi r
,Ph.D.
...._;:J-C-
Panagiotis D.Scaralatos, Ph.D..
Chair, DepartmentofCivil,Environmeniii ,
andGeomatics Engineering
MohammadIlyas, Ph.D.
Interim Dean, CollegeofEngineering
andComputerScience
b·l/~/
'UJ1'2.
Barry T.R son,Ph.D. Date ..
Dean, Graduate College
ii
ABSTRACT
Author: Eric Stanley
Title: Identifying Cost Savings through Energy Conservation Measures in Mechanically
Aerated Activated Sludge Treatment Processes in Southeast Florida

Institution: Florida Atlantic University
Thesis Advisor: Dr. Frederick Bloetscher
Degree: Master of Science
Year: 2012
This thesis presents a model which estimates energy and cost savings that can be realized by
implementing Energy Conservation Measures (ECMs) at mechanically aerated wastewater treatment plants
(WWTPs) in southeast Florida. Historical plant monitoring data is used to estimate savings achieved by
implementing innovative aeration technologies which include; 1) Fine Bubble Diffusers; 2) Single-Stage
Turbo Blowers; 3) Automatic Dissolved Oxygen (DO) Control. Key assumptions for modeling
performance of each technology are researched and discussed, such as trends in the future cost of
electricity, efficiency of blowers, and practical average DO levels for each scenario. Capital cost estimates
and operation and maintenance (O&M) costs are estimated to complete life-cycle cost and payback
analyses. The benefits are quantified on an individual and cumulative basis, to identify which technologies
are cost-beneficial. The results demonstrate that levels of payback of 20 years or less are available at the
three WWTPs studied.

iii
ACKNOWLEDGEMENTS
The author wishes to thank his wife, Tatyana, without whose love and support nothing would be
possible. The author also wishes to thank his employer, Hazen and Sawyer, P.C., including senior engineers
and coworkers, for providing a dynamic workplace environment supportive of furthering understanding of
complex engineering issues. The help of the utilities officials including Norm Wellings, Gabe Destio, and
Ed Catalano with the City of Boca Raton, and Chuck Flynn with the City of Plantation, was instrumental in
furthering the progress of this work. Lastly, the author would like to thank his thesis committee, including
Frederick Bloetscher, Ph.D., P.E., and Daniel Meerof, Ph.D, for their guidance in completing this thesis.

iv
IDENTIFYING COST SAVINGS THROUGH ENERGY CONSERVATION MEASURES IN
MECHANICALLY AERATED ACTIVATED SLUDGE TREATMENT PROCESSES IN SOUTHEAST
FLORIDA
LIST OF TABLES .........................................................................................................................................ix 
LIST OF FIGURES ..................................................................................................................................... xiii 
I. INTRODUCTION ....................................................................................................................................... 1 
1.1  Overview of the Aeration Process ................................................................................................. 3 
1.2  Less Efficient Mechanical Aeration Versus More Efficient Fine-Bubble Diffused Aeration ........ 5 
1.3  Less Efficient Multi-stage Centrifugal Blowers Versus More Efficient Single-stage Turbo
Blowers ....................................................................................................................................................... 6 
1.4  Less Efficient Manual DO Control Versus More Efficient Automatic DO Control ...................... 7 
1.5  Combining Technologies to Optimize Efficiency ........................................................................ 10 
1.6  Summary of Facilities Studied ..................................................................................................... 11 
II - LITERATURE REVIEW – DISCUSSION OF THE STATE OF THE ART IN ACTIVATED
SLUDGE PROCESS CONTROL AND KEY MODELING ASSUMPTIONS ............................................ 13 
2.1  Energy Conservation Measure Case Studies ................................................................................ 13 
2.2   Fine Bubble Diffusers .................................................................................................................. 17 
2.3   Blower Technology ...................................................................................................................... 18 
2.4   DO Control Strategy ................................................................................................................... 23 
2.4.1   Manual Control ........................................................................................................................ 23 
2.4.2   Automatic DO Control ............................................................................................................. 24 
2.4.3   DO Probes ................................................................................................................................ 25 
2.4.4   Modulating Valves ................................................................................................................... 25 
2.4.5   Flow Meters ............................................................................................................................. 26 
2.5   Piping ........................................................................................................................................... 27 
v
2.6   Summary of Technologies ........................................................................................................... 27 
2.7   Key Assumptions For Aeration Model ........................................................................................ 28 
2.7.1   DO Levels ................................................................................................................................ 28 
2.7.2   Blower Efficiency Assumptions .............................................................................................. 30 
2.7.3   Flowrate Assumptions ............................................................................................................. 30 
2.7.4   Aeration Modeling Global Assumptions ................................................................................. 31 
III. LITERATURE REVIEW – COST ESTIMATING METHODS AND ASSUMPTIONS ...................... 33 
3.1  Cost Estimate Level of Accuracy ................................................................................................ 33 
3.2   Life Cycle Cost Analysis Method And Assumptions .................................................................. 35 
3.3   Capital Cost ................................................................................................................................. 41 
3.3.1   Cost of Blower Technology ..................................................................................................... 42 
3.3.2   Cost of Fine Bubble Diffused Aeration Technology ............................................................... 43 
3.3.3  Foregone Capital Replacement Costs and Salvage Value ........................................................ 43 
3.4   Operation and Maintenance Costs ............................................................................................... 44 
IV. METHODOLOGY .................................................................................................................................. 46 
4.1  Identifying Specific Energy Conservation Measures .................................................................. 46 
4.2  Lifecycle Cost Analysis of ECMs ................................................................................................ 46 
4.2.1  Historical Plant Data ................................................................................................................ 49 
4.2.2  Estimating Yield ...................................................................................................................... 50 
4.2.3  Project Future Flows and Loadings ......................................................................................... 52 
4.2.4   Calculate Oxygen Requirement and Required Air Flowrates .................................................. 53 
4.2.5   Size Process Air Piping ............................................................................................................ 66 
4.2.6   Estimate Headloss Through Pipes and Create System Curve .................................................. 68 
4.2.7   Size Blowers ............................................................................................................................ 73 
4.2.8   Estimate Capital Cost ............................................................................................................... 77 
4.2.9  Estimate O&M and Foregone Capital Replacement Costs ...................................................... 78 
4.2.10  Energy Baseline – Estimated Energy Consumption of Existing Mechanical Aerators ............ 79 
vi
4.2.11  Complete Life Cycle Cost Analysis ......................................................................................... 81 
4.2.12  Model Accuracy Verification................................................................................................... 86 
V. PLANT ECM ASSESSMENT ................................................................................................................. 93 
5.1   City of Boca Raton WWTP ......................................................................................................... 93 
5.1.1   Boca Raton WWTP - Existing Secondary Treatment .............................................................. 93 
5.1.2   Boca Raton WWTP –Influent and Effluent Water Quality ...................................................... 95 
5.1.3   Boca Raton WWTP – Proposed ECM Design ......................................................................... 96 
5.1.4   Boca Raton WWTP - Results and Discussion ......................................................................... 97 
5.1.5   Boca Raton WWTP - Sensitivity Analysis ............................................................................ 101 
5.2   Broward County North Regional WWTP .................................................................................. 102 
5.2.1   Broward County North Regional WWTP - Existing Secondary Treatment .......................... 102 
5.2.2   Broward County North Regional WWTP –Influent and Effluent Water Quality .................. 103 
5.2.3   Broward County North Regional WWTP – Plant Specific Methodology
Considerations .................................................................................................................................... 104 
5.2.4   Broward County North Regional WWTP – Proposed ECM Design ..................................... 106 
5.2.5   Broward County North Regional WWTP – Results and Discussion ..................................... 107 
5.2.6   Broward County North Regional WWTP - Sensitivity Analysis ........................................... 112 
5.3   Plantation Regional WWTP ...................................................................................................... 113 
5.3.1   Plantation Regional WWTP - Existing Secondary Treatment .............................................. 113 
5.3.2   Plantation Regional WWTP – Influent and Effluent Water Quality ...................................... 113 
5.3.3   Plantation Regional WWTP – Proposed ECM Design .......................................................... 115 
5.3.4   Plantation Regional WWTP – Results and Discussion ......................................................... 115 
5.3.5   Plantation Regional WWTP - Sensitivity Analysis ............................................................... 119 
VI. DISCUSSION AND COMPARISON OF RESULTS .......................................................................... 121 
6.1   Improvement of Efficiency Comparison and Analysis .............................................................. 121 
6.2   Capital Cost Comparison and Analysis .................................................................................... 125 
6.3   Payback Comparison and Analysis ............................................................................................ 128 
vii
6.4   Sensitivity Analysis Comparison ............................................................................................... 132 
6.5   Total Savings And Regional Savings ......................................................................................... 136 
6.6   Current Energy Intensity Discrepancy and Potential Operational Modifications at
Plantation Regional WWTP .................................................................................................................... 136 
6.7   Ocean Outfall Rule Compliance ................................................................................................ 142 
6.8   Greenhouse Gas Emissions ........................................................................................................ 144 
VII. CONCLUSIONS AND RECOMMENDATIONS .............................................................................. 146 
7.1   Conclusions ................................................................................................................................ 146 
7.2   Recommendations ...................................................................................................................... 151 
APPENDICES ............................................................................................... Error! Bookmark not defined. 
BIBILIOGRAPHY ...................................................................................................................................... 268 

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LIST OF TABLES
Table 1.1 – Study Facility Summary ............................................................................................................. 12 
Table 2.1 – General ECM Case Study Survey .............................................................................................. 14 
Table 2.2 - Fine Bubble Diffuser Technologies with Highest SOTE’s ......................................................... 18 
Table 2.3 – Blower Technology Comparison ................................................................................................ 23 
Table 2.4 – Summary of Technologies .......................................................................................................... 28 
Table 2.5 – Manual DO Control - Case Study DO Levels ............................................................................ 29 
Table 2.6 – Automatic DO Control – Case Study DO Levels ....................................................................... 30 
Table 3.1 - AACE Estimate Class Level Characteristics (Christensen, 2005) .............................................. 34 
Table 3.2 – 2006 – 2011 AEO Report Average Predicted US Electricity Annual Real Inflation
Rates .............................................................................................................................................................. 39 
Table 3.3 – 2011 AEO Report Base and Side Case Assumptions ................................................................. 39 
Table 3.4 – Cost of Blower Technologies ..................................................................................................... 42 
Table 3.5 – Cost of Fine Bubble Diffusers .................................................................................................... 43 
Table 3.6 – Major Equipment Requiring Eventual Replacement .................................................................. 44 
Table 3.7 – Major Equipment Requiring Eventual Replacement .................................................................. 45 
Table 4.1 – Summary of Methodology .......................................................................................................... 48 
Table 4.2 – Boca Raton WWTP– Incremental Life-Cycle Cost Analysis ..................................................... 52 
Table 4.3 – Key Assumptions for ECMs ....................................................................................................... 57 
Table 4.4 – Extreme Weather Design Conditions ......................................................................................... 74 
Table 4.5 – Power Factor .............................................................................................................................. 80 
Table 4.6 – Predicted SCFM vs. Standard Oxygen Requirement based on Loading .................................... 90 
ix
Table 4.7 – Model Verification Sensitivity Analysis .................................................................................... 90 
Table 4.8 – Mechanically Aerated Module A, B, vs. Fine Bubble Aerated Module C Measured
Energy Usage Comparison ............................................................................................................................ 91 
Table 4.9 – Model Efficiency Gain Prediction Vs. Actual Efficiency Gain Prediction ................................ 92 
Table 5.1 – Study Facility Summary ............................................................................................................. 93 
Table 5.2 - Aeration Basin Characteristics .................................................................................................... 94 
Table 5.3 - Mechanical Aeration Characteristics .......................................................................................... 94 
Table 5.4 - Diffused Aeration Characteristics ............................................................................................... 94 
Table 5.5 - Blower Characteristics ................................................................................................................ 95 
Table 5.6 – Boca Raton WWTP – Design Influent/Effluent Based on 2007-2009 Flow/Loading
Data ............................................................................................................................................................... 95 
Table 5.7 – Boca Raton WWTP – Design Influent/Effluent Adjusted to Est. 2011-2031 Avg
Flowrate ......................................................................................................................................................... 96 
Table 5.8 – Boca Raton WWTP – Design Influent/Effluent Adjusted to Design Flow ................................ 96 
Table 5.9 – Life Cycle Cost Analyses Estimated Costs ................................................................................ 97 
Table 5.10 – Life Cycle Cost Analyses Estimated Savings ........................................................................... 97 
Table 5.11 – Boca Raton WWTP– Incremental Life-Cycle Cost Analysis ................................................... 99 
Table 5.12 – Boca Raton WWTP – Payback Sensitivity Analysis .............................................................. 101 
Table 5.13 - Aeration Basin Characteristics – Modules A and B ................................................................ 103 
Table 5.14 - Mechanical Aeration Characteristics – Modules A and B ...................................................... 103 
Table 5.15 – Broward Co. N. Regional WWTP – Design Influent/Effluent Based on 2004-2006 ............. 104 
Table 5.16 – Broward Co. N. Regional WWTP – Design Influent/Effluent Adjusted to Est. 2011-
2031 Avg Flow ............................................................................................................................................ 104 
Table 5.17 – Broward Co. N. Regional WWTP – Design Influent/Effluent Adjusted to Design
Flow ............................................................................................................................................................ 104 
Table 5.18 – 2004-2006 # of Basins In Service vs. Flowrate ...................................................................... 105 
Table 5.19 – Projected Module D Energy Reduction .................................................................................. 106 
Table 5.20 – Life Cycle Cost Analyses Estimated Costs ............................................................................ 107 
Table 5.21 – Life Cycle Cost Analyses Estimated Savings ......................................................................... 108 
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