m
&EPA
United States
Environmental Protection
Agency
Evaluation of
Energy Conservation
A Measures
>r Wastewater Treatment Facilities
EPA 832-R-10-005 SEPTEMBER 2010
-------
U.S. Environmental Protection Agency
Office of Wastewater Management
1200 Pennsylvania Avenue NW
Washington, DC 20460
EPA832-R-10-005
September 2010
Cover photo:
Bucklin Point WWTF, MA. Photo courtesy of Narragansett Bay Commission.
Cover insert photos (left to right):
High Speed Magnetic Bearing Turbo Blower at the De Pere WTF, Wl. Photo courtesy of Green Bay
Metropolitan Sewerage District.
Oxidation Ditch with Aeration Rotor at the City of Bartlett WWTP #1, TN. Photo courtesy of City of
Bartlett Wastewater Division.
Variable Outlet Vane Diffuser. Photo courtesy of Turblex, Inc.
Evaluation of Energy Conservation Measures ii September 2010
-------
Preface
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the nation's
land, air, and water resources. Under a mandate of environmental laws, the Agency strives to formulate
and implement actions leading to a balance between human activities and the ability of ecosystems to
support and sustain life. To meet this mandate, the Office of Wastewater Management (OWM) provides
information and technical support to help solve environmental problems today and to build the
knowledge base necessary to protect public health and the environment well into the future. This
document was prepared under contract to EPA, by The Cadmus Group. The document provides
information on current state-of-development as of the publication date; however, it is expected that
this document will be revised periodically to reflect advances in this rapidly evolving area. Except as
noted, information, interviews, and data development were conducted by the contractor. While there
are many proven, cost-effective energy conservation practices and numerous new technologies or
modifications of existing technologies available for detailed study, the case studies in this document
were selected on the basis of specific criteria. The criteria included the ability to provide as least one
year of full-scale operating and performance data, capability of providing detailed capital, operations,
and maintenance cost breakdowns, and the ability to provide the data within the time frame established
for completing the document. It is anticipated that as the document is updated, additional case studies
on new technologies could be included.
Disclaimer
This information represents new, innovative or emerging approaches, techniques, or technologies that
may assist utility owners and operators reduce the capital or operating costs of wastewater treatment.
Some of the information, especially related to emerging technologies, was provided by the
manufacturer or vendor of the equipment or technology, and could not be verified or supported by a
full-scale case study. In some cases, cost data were based on estimated savings without actual field
data. When evaluating technologies, estimated costs, and stated performance, efforts should be made
by the reader to collect current and more up-to-date information.
The mention of trade names, specific vendors, or products does not represent an actual or presumed
endorsement, preference, or acceptance by EPA or the federal government. Stated results, conclusions,
usage, or practices contained herein may be different depending on specific site conditions and do not
necessarily represent the views or policies of EPA.
This document has been reviewed in accordance with EPA's peer and administrative review policies and
approved for publication
Evaluation of Energy Conservation Measures Hi September 2010
-------
Acknowledgements
This document was prepared by The Cadmus Group, Inc. (Cadmus) under EPA Contract No. GS-10F-
0273K C/l-1, Task Order 311. The Cadmus Team was led by Laura Dufresne and Stephen Couture of
Cadmus and David Reardon and Kenneth Henderson of HDR. EPA technical direction and oversight were
provided by James Wheeler and Phil Zahreddine, EPA Office of Wastewater Management.
The project was supported by a technical expert panel consisting of the following individuals:
Kathleen O'Conner, New York State Energy Research and Development Authority
Joe Cantwell, SAIC
Mike Wilson, CH2M Hill
Steve Bolles, Process Energy Services
Andre Schmidt, Los Angeles County Sanitation Districts - Energy Recovery Engineering Services
Jess Burgess, Consortium for Energy Efficiency
A formal peer review of the draft document was conducted by the following individuals:
Thomas E. Jenkins, JenTech Inc.
Julia Gass, Black & Veatch
George Lawrence, Efficiency Vermont
George Crawford, CH2M HILL
Additional review was provided by David Redmon of Redmon Engineering Company, Andrew Shaw of
Black & Veatch, and Andrew Truman of Black & Veatch.
While every effort was made to accommodate all of the Peer Review comments, the results and
conclusions do not indicate consensus and may not represent the views of all the reviewers.
The authors sincerely appreciate the review and guidance provided by the technical expert panel
members and peer reviewers.
Evaluation of Energy Conservation Measures iv September 2010
-------
Acronyms and Abbreviations
ACEEE
APPA
ASCE
ASE
AWWA
BEP
bhp
BNR
BOD
CCCSD
CEC
CEE
CFO
CHP
DCS
DO
DOE
DSIRE
ECM
EPACT
EPC
EPRI
ESCO
GBMSD
gpm
hp
l&l
IDA
IUVA
kW
kWh
LPHO
MBR
mg
mgd
MLE
MPN
NAESCO
NEMA
NYSERDA
PG&E
PLC
PSAT
psi
psig
American Council for an Energy Efficient Economy
American Public Power Association
American Society of Civil Engineers
Alliance to Save Energy
American Water Works Association
Best Efficiency Point
Brake Horsepower
Biological Nutrient Removal
Biochemical Oxygen Demand
Central Contra Costa Sanitary District
California Energy Commission
Consortium for Energy Efficiency
Cost Flow Opportunity
Combined Heat and Power
Distributed Control System
Dissolved Oxygen
Department of Energy
Database of State Incentives for Renewables and Efficiency
Energy Conservation Measure
Energy Policy Act
Energy Performance Contracting
Electric Power Research Institute
Energy Services Company
Green Bay (Wisconsin) Metropolitan Sewerage District
Gallons per minute
Horsepower
Inflow and infiltration
International Ozone Association
International Ultraviolet Association
Kilowatt
Kilowatt hour
Low Pressure High Output
Membrane Bioreactor
Million Gallons
Million Gallons per Day
Modified Ludzack-Ettinger process
Most Probable Number
National Association of Energy Service Companies
National Electrical Manufacturers Association
New York State Research and Development Authority
Pacific Gas and Electric
Programmable Logic Controller
Pump System Assessment Tool
Pounds per Square Inch
Pounds per Square Inch Gauge
Evaluation of Energy Conservation Measures
September 2010
-------
rpm
SRT
TDH
TSS
TVA
UV
UVT
VFD
W
WEF
WEFTEC
WERF
WMARSS
WPCP
WRF
WSU
WWTP
Revolutions per Minute
Solids Residence Time
Total Dynamic Head
Total Suspended Solids
Tennessee Valley Authority
Ultraviolet Light
UVtransmittance
Variable Frequency Drive
Watt
Water Environment Federation
Water Environment Federation Technical Exhibition and Conference
Water Environment Research Foundation
Waco Metropolitan Area Regional Sewer System
Water Pollution Control Plant
Water Research Foundation
Washington State University
Wastewater Treatment Plant
Evaluation of Energy Conservation Measures
September 2010
-------
Contents
1. Introduction 1-1
1.1 Background 1-1
1.2 Purpose and Audience 1-2
1.3 Report Organization 1-3
1.4 Summary of Innovative and Emerging ECMS 1-4
1.5 References 1-6
2. Recommended Approach to Energy Management 2-1
2.1 Introduction 2-1
2.2 Recommended Approach 2-1
2.3 Tools for Energy Management 2-4
2.4 Financing Resources 2-4
2.5 Other ECMs and Resources 2-6
2.6 References 2-7
3. Energy Conservation Measures for Pumping Systems 3-1
3.1 Introduction 3-1
3.2 Pumping System Design 3-3
3.3 Motors 3-5
3.3.1 Motor Efficiency and Efficiency Standards 3-6
3.3.2 Motor Management Programs 3-7
3.3.3 Innovative and Emerging Technologies 3-8
3.4 Power Factor 3-9
3.5 Variable Frequency Drives (VFDs) 3-10
3.5.1 Energy Savings 3-11
3.5.2 Applications 3-11
3.5.3 VFD Strategies for Wastewater Pumping Stations 3-12
3.6 References 3-13
4. Design and Control of Aeration Systems 4-1
4.1 Introduction 4-1
4.2 ECMs for Aeration Systems 4-1
4.2.1 ECMs for Diffused Aeration Systems 4-2
4.2.2 ECMs for Mechanical Aerators 4-5
4.3 Control of the Aeration Process 4-7
4.3.1 Automated DO Control 4-7
4.3.1.1 DO Measurement Equipment 4-10
4.3.1.2 Advances in DO Control Strategies 4-13
4.3.2 Emerging Technologies Using Control Parameters other than DO 4-15
4.4 Innovative and Emerging Control Strategies for Biological
Nutrient Removal 4-18
Evaluation of Energy Conservation Measures vii September 2010
-------
4.5 References 4-20
5. Blower and Diffuser Technology for Aeration Systems 5-1
5.1 Introduction and Comparison of Blower Types 5-1
5.2 High-Speed Gearless (Turbo) Blowers 5-5
5.3 Single-Stage Centrifugal Blowers with Inlet Guide Vanes and Variable
Diffuser Vanes 5-11
5.4 New Diffuser Technology 5-15
5.5 References 5-19
6. Innovative and Emerging Energy Conservation Measures for Selected
Treatment Processes 6-1
6.1 Introduction 6-1
6.2 UV Disinfection 6-1
6.2.1 Design 6-3
6.2.2 Operation and Maintenance 6-5
6.3 Membrane Bioreactors (MBRs) 6-6
6.4 Anoxic and Anaerobic Zone Mixing 6-8
6.4.1 Hyperbolic Mixer 6-8
6.4.2 Pulsed Large Bubble Mixing 6-12
6.5 References 6-13
7. Energy Conservation Measures for Solids Processing 7-1
7.1 Introduction 7-1
7.2 Digestion 7-1
7.3 Incineration 7-4
7.4 Thermal Drying 7-6
7.5 References 7-9
8. Summary of Facility Case Studies 8-1
8.1 Introduction 8-1
8.2 Approach 8-1
8.3 Summary of Results 8-3
Appendix A: Facility Case Studies
Appendix B: Web Resources
Evaluation of Energy Conservation Measures viii September 2010
-------
List of Tables
Table 1-1. Innovative and Emerging ECMs 1-5
Table 3-1. Pump System Efficiency 3-2
Table 5-1. Overview of Blower Types of Aeration of Wastewater 5-2
Table 5-2. Manufacturer Cost Ranges for Select Blower Types 5-3
Table 5-3. Typical Blower Efficiencies 5-4
Table 5-3. Examples of Turbo Blower Manufacturers in the North American Market 5-8
Table 5-4. Net Present Worth of Blower Selections for the City of Oneida (2003$) 5-14
Table 6-1. Disinfection Equipment Power and Cost Estimates (55 mgd Peak Flow,
38 mgd Average Flow, 65% Design UVT) 6-4
Table 8-1. Summary of Facility Case Studies 8-4
Evaluation of Energy Conservation Measures ix September 2010
-------
List of Figures
Figure 1-1. Typical Energy Use Profile for 10-mgd Secondary Treatment Processes 1-2
Figure 2-1. Steps in the Plan-Do-Check-Act Management Systems Approach 2-2
Figure 3-1. Vector Relationship of AC Power 3-9
Figure 3-2. Wasted Energy in Alternative Control Schemes Compared to
Variable Frequency Drives 3-11
Figure 4-1. Eimco Water Technologies Carrousel System Excell® Aerator II 4-6
Figure 4-2. Common Cascade System for Automated DO Control 4-10
Figure 4-3. Optical DO Sensor Operation 4-12
Figure 4-4. Integrated Air Flow Control System for Automated DO Control 4-14
Figure 4-5. Flow-Through Respirometry Cell 4-16
Figure 4-6. Representation of BIOS Process 4-17
Figure 4-7. Representation of the Bios Process 4-19
Figure 5-1. Example of High-Speed Turbo Blower with Air Bearings (HIS) 5-6
Figure 5-2. Example of High-Speed Turbo Blower with Mechanical Bearings
(Atlas Copco) 5-6
Figure 5-3. Comparison of Power Draw for Old and New Blower at Burlington, VT 5-11
Figure 5-4. Example of Single-Stage Centrifugal Blower with Inlet Guide Vanes and
Variable Diffuser Vanes by Turblex® 5-11
Figure 5-5. Example of Single-Stage Centrifugal Blower with Inlet Guide Vanes and
Variable Diffuser Vanes by Dresser Roots 5-11
Figure 5-6. Variable Outlet Vane Diffuser from Turblex® 5-12
Figure 5-7. Ultra-fine Pore Membrane Aeration Panel 5-15
Figure 5-8. AeroStrip® Diffuser by the Aerostrip Corporation 5-16
Figure 6-1. Example UV Lamp Configurations for Wastewater Treatment 6-2
Figure 6-2. Typical Installation of a Hyperboloid Mixer 6-9
Figure 6-3. Conventional Hydrofoil Mixer 6-11
Figure 6-4. Typical BioMix™ Installation 6-12
Figure 7-1. Vertical Linear Motion Mixer by Enersave Fluid Mixers, Inc 7-3
Figure 7-2. Schematic Representation of Multiple Hearth Incinerator Energy Efficiency
Improvements at WSSC Western Branch WWTP 7-6
Figure 7-3. Example of Solar Dryer by Parkson 7-8
Evaluation of Energy Conservation Measures x September 2010
-------
1. Introduction
Chapter 1 covers:
1.1 Background
1.2 Purpose and Audience
1.3 Report Organization
1.4 Summary of Innovative and Emerging ECMs
1.5 References
1.1 Background
Providing reliable wastewater services and safe drinking water is a highly energy-intensive
activity in the United States. A report prepared for the Electric Power Research Institute (EPRI) in 1996
estimated that by the end of that year, the energy demand for the water and wastewater industry
would be approximately 75 billion kilowatt hours (kWh) per year, or about 3 percent of the electricity
consumed in the U.S. (Burton 1996). The Consortium for Energy Efficiency (CEE) now estimates the
annual energy usage at approximately 100 billion kWh per year (Burton 1996, extrapolated by CEE). At
an average energy cost of $0.075 per kWh, the cost for providing safe drinking water and providing
effective wastewater treatment is approximately $7.5 billion per year.
Energy is used throughout the wastewater treatment process; however, pumping and aeration
operations are typically the largest energy users (see Figure 1-1 for a typical energy use profile for a
medium sized wastewater treatment plant). Energy costs in the wastewater industry are rising due to
many factors, including:
• Implementation of more stringent effluent requirements, including enhanced removal of
nutrients and other emerging contaminants of concern that may, in some cases, lead to the use
of more energy intensive technologies.
• Enhanced treatment of biosolids including drying/pelletizing.
• Aging wastewater collection systems that result in additional inflow and infiltration, leading to
higher pumping and treatment costs.
• Increase in electricity rates.
As a consequence of these rising costs, many wastewater facilities have developed energy management
strategies and implemented energy conservation measures (ECMs). Using the figures provided earlier in
this section, improving the energy efficiency of America's drinking water and wastewater systems by 10
percent could save more than 10 billion kWh each year, representing a cost savings of approximately
$750 million annually.
Evaluation of Energy Conservation Measures 1-1 September 2010
-------
2.0
_ 1
„ . ^ _ , s
- - - • jg
f
v
(
1
1
Main
Pumping
Primary
Treatment
Secondary
Treatir»nt
Sludge
Treatment
Figure 1-1. Typical Energy Use Profile for 10-mgd Secondary Treatment Processes.
Source: WEF 2009, Figure 7.1. Used with permission.
Note: energy use for various treatment processes will vary greatly from plant to plant. Advanced treatment
processes may require more energy than conventional treatment processes and may not be represented in this
figure.
1.2 Purpose and Audience
The purpose of this report is to encourage the implementation of ECMs at publicly owned
treatment works (POTWs) by providing accurate performance and cost/benefit information for such
projects. The report's focus is mainly on energy efficient equipment replacement, operational
modifications, and process control enhancements that lead to improved energy efficiency and cost
savings with reasonable payback periods (10 years or less). The scope of the report does not include
cogeneration technologies (also known as combined heat and power, or CHP) or alternative/renewable
energy technologies, as the information on these topics is being developed by EPA under separate
projects. The main audiences for this report are POTW managers, owners, and operators who may be
considering the implementation of ECMs and states or other agencies who may be interested in
supporting such projects.
This report includes summary information on conventional ECMs that are in use in the U.S. and
have a strong track record of success with respect to energy conservation; however, the focus is
identification of innovative and emerging ECMs. For the purposes of this document, innovative and
emerging are defined as follows:
• Innovative: technologies that may be established overseas and have either been tested in the
U.S. as a full-scale demonstration project or installed at a U.S. wastewater treatment plant
Evaluation of Energy Conservation Measures
1-2
September 2010
-------
(WWTP) for at least one year but not more than 5 years. For a technology that meets the above
criteria to be considered innovative rather than emerging, independent test data showing
energy savings must be presented in the literature or documented in this report in one of the
facility case studies. Innovative technologies include modifications and new applications for
established technologies.
• Emerging: technologies in the development or testing stage in the U.S. and that show potential
for energy savings and relatively short payback periods, but for which independent full-scale
demonstration or operating data are not yet available.
See Section 1.4 for a summary of innovative and emerging ECMs identified in this report.
This report builds upon an extensive literature review of the effectiveness and costs of ECMs for
municipal wastewater treatment and solids processing. Additionally, a panel of technical experts
provided input on the implementation of various ECMs. Detailed facility assessments of nine wastewater
treatment facilities are provided, including detailed information on ECM implementation, energy
savings, and cost data.
1.3 Report Organization
The report is organized into nine chapters and two appendices as follows:
• Chapter 1, Introduction, presents background, purpose, audience, and organization for the
report.
• Chapter 2, Recommended Approach to Energy Management, presents a comprehensive
approach to energy management at a wastewater treatment utility, including developing an
energy management program. It lists available tools and financing resources that can help
utilities implement their programs. It also lists other ECMs that should be considered by
wastewater utilities but are not the focus of this report.
• Chapter 3, Energy Conservation Measures for Pumping Systems provides an overview of
conventional ECMs related to pumping design, variable frequency drives (VFDs), and motors and
refers the reader to industry standards and web links for additional guidance.
• Chapter 4, Design and Control of Aeration Systems, provides detailed information on ECMs
related to the design of aeration systems and automated aeration control, including
conventional control based on dissolved oxygen (DO) measurements and emerging control
strategies. Innovative and emerging technologies for automated control of biological nitrogen
removal are also discussed.
• Chapter 5, Blower and Diffuser Technology for Aeration Systems, describes innovative ECMs
related to blower and diffuser equipment. It includes a summary of various blower types such as
single-stage centrifugal, high-speed turbo, and screw compressors in addition to new diffuser
technology.
• Chapter 6, Innovative and Emerging Energy Conservation Measures for Selected Treatment
Processes, provides a discussion of ECMs for advanced technologies (UV disinfection,
Evaluation of Energy Conservation Measures 1-3 September 2010
-------
membranes, and anoxic zone mixing) and presents full-scale plant test results where available.
For ECMs that are technically feasible and promising for the industry but where operating data
are not available, manufacturer's information is provided.
• Chapter 7 - Energy Conservation Measures for Solids Processing, describes innovative EMS for
digestion, incineration, and thermal drying and provides supporting data from case histories.
• Chapter 8, Summary of Facility Case Studies, describes the approach used to select the nine
facility case studies and summarizes case study findings in narrative form and in summary
tables.
• Appendix A, Facility Case Studies, contains detailed information and results from nine facility
case studies.
• Appendix B, Web Resources, provides resources for further information. Categories of web
resources include books available from online retailers; government publications through U.S.
Department of Energy (DOE) and U.S. Environmental Protection Agency (EPA); information
available from nonprofit organizations, state programs, Water Environment Research
Foundation (WERF) and Water Research Foundation (WaterRF); and online journals and
conference proceedings.
1.4 Summary of Innovative and Emerging ECMs
Table 1-1 lists the innovative and emerging ECMs identified in this report and references the
specific report section for more information. As stated in Section 1.2, independent demonstration or
full-scale operating data documenting energy savings are required for a new technology to be
considered "innovative;" otherwise, it was classified as "emerging" in this report. Note that this report
describes many other conventional ECMs that can achieve significant energy savings.
Evaluation of Energy Conservation Measures 1-4 September 2010
-------
Table 1-1. Innovative and Emerging ECMs
Chapter
4 - Design and Control
of Aeration Systems
5- Blower and Diffuser
Technology for
Aeration Systems
6- Innovative and
Emerging Energy
Conservation Measures
for Selected Treatment
Processes
7 -Energy Conservation
Measures for Solids
Processing
ECM Name
Intermittent Aeration
Dual Impeller Aerator (mechanical mixing)
Integrated airflow control
Automated SRT/DO Control
Respirometry for aeration control
Critical oxygen point control
Off -gas monitoring and control
Online monitoring and control of nitrification
using nicotinamide adenine dinucleotide (NADH)
(Symbio® process)
Bioprocess Intelligent Optimization System (BIOS)
High-speed gearless (Turbo) blowers
Single-stage centrifugal blowers with inlet guide
vanes and variable diffuser vanes
Ultra-fine bubble diffusers
New diffuser cleaning technology
Low-pressure high-output lamps for UV
disinfection
Automated channel routing for UV disinfection
Membrane air scour alternatives
Hyperbolic mixers
Pulsed Large Bubble Mixing (e.g., BioMx)
Vertical linear motion mixer
Upgrading multiple hearth furnaces to
incorporate waste heat recovery/combustion air
pre-heating
Solar drying
ECM Categorization
and Report Section
Emerging -4. 2.1
Emerging -4. 2. 2
Innovative -4.3.1
Innovative- 4.3.1
Emerging -4. 3. 2
Emerging -4. 3. 2
Emerging -4. 3. 2
Emerging -4.4
Emerging -4.4
Innovative -5. 2
Innovative -5. 3
Emerging -5.4
Emerging -5. 5
Emerging -6. 2.1
Emerging -6. 2. 2
Emerging -6. 3
Innovative -6. 4.1
Innovative -6. 4.2
Innovative -7. 2
Innovative -7. 3
Emerging -7.4
Evaluation of Energy Conservation Measures
1-5
September 2010
-------
1.5 References
Burton, Franklin L. 1996. Water and Wastewater Industries: Characteristics and Energy Management
Opportunities. Burton Environmental Engineering, Los Altos, CA. Prepared for the Electric Power
Research Institute. Palo Alto, California. Report CR106941. September, 1996.
Cams, K., 2005. Bringing Energy Efficiency to the Water & Wastewater Industry: How Do We Get There?
In WEFTEC 2005 Proceedings.
Water Environment Federation (WEF). 2009. Manual of Practice (MOP) No. 32: Energy Conservation in
Water and Wastewater Facilities. Prepared by the Energy Conservation in Water and Wastewater
Treatment Facilities Task Force of the Water Environment Federation. McGraw Hill, New York.
USEPA. 2008. Ensuring a Sustainable Future: An Energy Management Guidebook for Wastewater and
Water Utilities. January 2008. Available online:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook si energymanagement.pdf
Evaluation of Energy Conservation Measures 1-6 September 2010
-------
2. Recommended Approach to Energy Management
Chapter 2 covers:
2.1 Introduction
2.2 Recommended Approach
2.3 Tools for Energy Management
2.4 Financing Resources
2.5 Other ECMs and Resources
2.6 References
2.1 Introduction
Equipment upgrades and operational modifications to reduce energy use should not be one-
time events, but should be incorporated into a comprehensive energy review and management strategy.
Section 2.2 presents EPA's recommended approach to energy management for wastewater utilities. On-
line tools and financing resources are available to utilities interested in developing an energy
management strategy and are described in Sections 2.3 and 2.4 respectively.
As explained in Chapter 1, the scope of this document is energy conservation measures (ECMs)
related to equipment upgrades and operations strategies, with a focus on innovative and emerging
technologies. These are only a subset, however, of the ECMs available to wastewater utilities. Section
2.5 lists other types of ECMs (mainly conventional) and provides references for additional information.
2.2 Recommended Approach
To optimize energy savings at a wastewater treatment plant (WWTP) now and in the future,
ECMs should be evaluated and implemented as part of a comprehensive energy management program.
In order to assist utilities in developing such a program, the EPA Office of Wastewater Management
developed a guidebook entitled Ensuring a Sustainable Future: An Energy Management Guidebook for
Wastewater and Water Utilities (USEPA, 2008a)
http://www.epa.gov/waterinfrastructure/pdfs/guidebook si energymanagement.pdf, which notes that:
More and more utilities are realizing that a systematic approach for managing the full range of
energy challenges they face is the best way to ensure that these issues are addressed on an
ongoing basis in order to reduce climate impacts, save money, and remain sustainable (EPA
2008, p. 3).
This EPA guidebook recommends the plan-do-check-act management system approach for energy
conservation and management as shown in Figure 2.1. This basic approach is applicable to all utility
operations and not solely to energy management activities. However, the approach has been expanded
and tailored to water and wastewater utilities in a simple 9-step approach shown in the text box
following Figure 2.1. These key steps for success are based on experience of water and wastewater
utilities that have gone through the process of identifying and implementing ECMs. Note that in the 9-
step approach, identifying ECMs does not come into play until Step 6, Devise a Plan.
Evaluation of Energy Conservation Measures 2-1 September 2010
-------
Figure 2-1. Steps in the Plan-Do-Check-Act Management Systems Approach
Source: USEPA2008b
Evaluation of Energy Conservation Measures
2-2
September 2010
-------
Recommended 9-Step Approach to Energy Management
1. Create an Energy Sustainability Team. Identify an energy program management team with
responsibility for implementing the improvement program from start to finish. Create a core
team with representatives from all aspects of operations, maintenance and management.
Consider appointing an Energy Manager whose only responsibility is energy conservation (and
possibly recovery) for your facility.
2. Gather Data. Gather data on energy use (e.g., from gas, fuel oil and electricity bills). Make this
data available to the team.
3. Benchmark Performance. Create a baseline of energy performance against which you can
measure improvements over time. You can do this using ENERGY STAR'S Portfolio Manager for
wastewater treatment plants, available online at
http://www.energystar.gov/index.cfm?c=water.wastewater drinking water. Portfolio
Manager has the benefit of converting all types of energy use (e.g., natural gas, fuel oil, and
electricity) to a common unit so that they can be added together, and provides an estimate of
greenhouse gas emissions. You may also be able to compare your utility's performance to
similar utilities if you meet certain criteria.
4. Conduct an Energy Audit. Determine the energy use of various processes and identify
opportunities for energy use reduction.
5. Develop Goals. Identify quantifiable energy improvement goals that complement your utility's
mission, goals, and strategic direction.
6. Devise a Plan. Identify Energy Conservation Measures (ECMs) and develop a plan for
implementing them. Start with "low hanging fruit" and focus on energy intensive operations
such as aeration and pumping. Consider renewable energy options and opportunities for
energy generation using alternative methods. Determine costs and payback periods for
various options.
7. Implement Improvements. Assign responsibilities and establish deadlines. Consider
alternative financing approaches. Fully engage and train your operations staff.
8. Monitor and Measure Results. Track performance, review progress towards energy goals, and
develop a plan for maintaining energy efficient equipment. Re-evaluate your goals in light of
new information and priorities, and make changes to your program as necessary.
9. Communicate Success. Communicate the successes of your energy management program to
employees, utility management, and your community.
Evaluation of Energy Conservation Measures 2-3 September 2010
-------
2.3 Tools for Energy Management
A number of tools have been developed to help wastewater utilities implement an energy
management program. Data management tools that are available online include:
• The ENERGY STAR benchmarking tool Portfolio Manager provides a way for utilities to track
their energy use as well as compare their performance to utilities with similar size and
treatment goals. It is available free online at
http://www.energystar.gov/index.cfm?c=water.wastewater drinking water. See
http://www.energystar.gov/index.cfm?c=business.bus internet presentations for details
regarding regular web-based training.
• Pump and motor management tools (see Chapter 3 for more information):
- The Pumping System Assessment Tool (PSAT), developed by the Department of Energy
(DOE) and available free online at
http://wwwl.eere.energy.gov/industrv/bestpractices/software psat.html can help users
determine the efficiency of their existing pumping systems and calculate energy and cost
savings for upgrades.
MotorMaster+ is a motor selection and management tool, available for free online at
http://www.motorsmatter.org/. It includes inventory management features, maintenance
logging, efficiency analysis, savings evaluation, and energy accounting. It includes a catalog
of 17,000 motors from 14 manufacturers, including NEMA Premium® efficiency motors, and
motor purchasing information.
2.4 Financing Resources
Funding energy conservation projects is an important component of an energy management
program, particularly due to limited resources available to utilities and the need to meet multiple
environmental objectives and regulatory requirements. A number of funding options, however, are
available to a utility. The California Energy Commission (CEC) notes that:
A shortage of internal funds need not be a "barrier" to implementing energy efficiency projects.
There are plenty of financing sources, programs and options available to serve you. Real barriers
are due to the lack of awareness or understanding of the:
1) many benefits of investing in energy efficiency projects. These benefits include
energy cost savings, increased revenues, improved worker comfort and productivity,
reduced maintenance cost of old, inefficient equipment, and reduction of
environmental degradation and
Evaluation of Energy Conservation Measures 2-4 September 2010
-------
2) many programs for financing energy efficiency projects (CEC 2000)1.
Capital projects for publically-owned wastewater utilities have historically received funding from
grants and loans; however, third party financing (e.g., state energy offices, energy services companies) is
becoming more common. In many parts of the U.S., energy performance contracting (EPC) has been
used to finance energy efficiency improvements (Zobler 2009). Properly structured performance
contracts can be considered in the utility's operating budget instead of as a capital expense. Examples
include energy service provider-based financing and tax exempt lease-purchase agreements.
One option to streamline the audit, financing, and implementation steps of an energy
management program is to hire an Energy Services Company (ESCO). ESCOs usually develop and manage
EPCs, manage a wide range of tasks, and assume some or most of the technical and performance risk
associated with the project. See the National Association of Energy Service Companies (NAESCO)
website at http://www.naesco.org/for more information and a list of service providers in your area.
Additional guidance is available in the CEC's Handbook, "How to Hire an Energy Services Company " (CEC
2000), available online at http://www.energy.ca.gov/reports/efficiencv handbooks/400-00-001D.PDF.
In addition to the above resources, other free tools and resources are available to help
wastewater utilities finance ECMs. Examples are provided below.
• The Clean Water State Revolving Fund (CWSRF), offering low interest loans (average 2.2
percent) for wastewater treatment improvements. The program is administered by individual
states - A list of regional and state contacts is available online at
http://www.epa.gov/owm/cwfinance/cwsrf/contacts.htm.
• Financing guidance from ENERGY STAR, available online at
http://www.energystar.gov/index.cfm?c=business.bus financing. Includes a spreadsheet-based
Cash Flow Opportunity (CFO) Calculator that can help plant managers calculate simple payback
as well as cost of delay, which is the lost opportunity cost if the project is delayed 12 months or
more.
• Database of State Incentives for Renewables and Efficiency (DSIRE), available online at
http://www.dsireusa.org/ is a comprehensive source of information on state, local, utility, and
federal incentives and policies that promote renewable energy and energy efficiency.
Established in 1995, DSIRE is an ongoing project of the North Carolina Solar Center and the
Interstate Renewable Energy Council, which is funded by the U.S. Department of Energy (DOE).
• Report by the CEC titled "How to Finance Public Sector Energy Efficiency Projects" (CEC 2000),
available online at http://www.energy.ca.gov/reports/efficiencv handbooks/400-00-001A.PDF.
Includes a description of cost-effectiveness criteria and options for financing energy efficiency
projects.
1 For more information, see the CEC report, How to Finance Public Sector Energy Efficiency Projects. January 2000.
Available online at http://www.energy.ca.gov/reports/efficiency handbooks/400-00-001A.PDF
Evaluation of Energy Conservation Measures 2-5 September 2010
-------
2.5 Other ECMs and Resources
Although the focus of this document is to report on innovative and emerging equipment and
operations related ECMs, other ECMs (both innovative and conventional), have been used successfully
at WWTPs to save energy and associated costs, such as:
• Lighting, HVAC, and other building improvements.
• Reducing the loading to the WWTPs by:
Collection system improvements to reduce infiltration and inflow to reduce storm-
related peaks
- Water conservation
Use of equalization basins to attenuate peak flows and loadings
• Use of Supervisory Control and Data Acquisition (SCADA) software for process monitoring
and operational control. SCADA has many operational benefits, including:
It can provide data for process modeling and energy use optimization
It can provide immediate detection of problems through diagnostic displays, enabling
quick intervention for fast resolutions
It can allow operators to compensate for seasonal flow and wet weather by
automatically adjusting setpoints (USEPA 2006).
• Implementing cogeneration technology to generate electricity and recoverable heat onsite
using methane off-gas from anaerobic digesters.
• Implementing energy management strategies such as
Hiring an energy manager
Real-time power monitoring
Peak electric demand reduction
Submetering to identify the most energy intensive processes
Other ECMs that can offer modest improvements and may be easy for a system to implement include
pump coatings to reduce friction or installing a vortex grit removal system instead of one that uses
aeration.
ECMs should always be considered when a plant is facing a major 20 or 30 year upgrade. At this
time, there are opportunities to reconfigure the plant for energy savings. Noted in Chapters 3 and 4 of
this document but worth reiterating is the importance of properly designing for energy efficiency.
Maximizing equipment (blower and pump) turndown capacity and designing for plant upgrades in stages
(i.e., "right sizing") can go a long way to meet energy efficiency goals. Another important design
concept is to use hydraulic head whenever possible to reduce the need to pump. The Consortium for
Energy Efficiency (CEE) has recently issued guidance on how to include energy efficiency in requests for
qualifications (RFQs) and Requests for Proposals (RFPs). This guidance is available free online at
http://www.ceel.org/ind/mot-sys/ww/rfp/index.php3.
Evaluation of Energy Conservation Measures 2-6 September 2010
-------
Appendix B of this report provides a comprehensive list of web references for energy
conservation. Other important technical references include the Water Environment Federation (WEF)
Manual of Practice (MOP) No. 32: Energy Conservation in Water and Wastewater Facilities (WEF 2009)
and the report by the Electric Power Research Institute (EPRI), Quality Energy Efficiency Retrofits for
Wastewater Systems (EPRI 1998). The WEF MOP 8, Design of Municipal Wastewater Treatment Plants
(WEF and ASCE 2010) provides guidance on designing energy efficient wastewater treatment plant
components. The WERF report, Energy Efficiency in Wastewater Treatment in North America: A
Compendium of Best Practices and Case Studies of Novel Approaches, provides recommendations on
energy efficiency improvements both through optimization of current processes and through adoption
of novel approaches. The report is scheduled to be published in January 2011. Lastly, the WERF report,
Best Practices for Sustainable Wastewater Treatment: Initial Case Study Incorporating European
Experience and Evaluation Tool Concept (2009), highlights European case studies related to energy
efficiency in wastewater treatment.
Additional online resources for comprehensive energy management include:
• Ensuring a Sustainable Future: An Energy Management Guidebook for Wastewater and Water
Utilities (USEPA 2008a). This document provides a step-by-step method for energy conservation
based on the Plan-Do-Check-Act management approach. It is available online at:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook si energymanagement.pdf
• EPA's Wastewater Management Fact Sheet: Energy Conservation (USEPA 2006), available online
at: http://www.epa.gov/owm/mtb/energycon fasht final.pdf. This 7-page fact sheet describes
possible practices that can be implemented to conserve energy at a WWTP.
• The Flex Your Power Best Practices Guide for Local Governments, Wastewater Sector, available
online at: http://www.fypower.org/bpg/module.html?b=institutional&m=Water Use. This
guide contains a 4-step approach to reducing energy use at a WWTP and includes links to
additional online resources.
• Wisconsin Focus on Energy's Water and Wastewater Energy Best Practice Guidebook (Focus on
Energy 2006), available online at:
http://www.werf.org/AM/Template.cfm?Section=Home&TEMPLATE=/CM/ContentDisplay.cfm&
CONTENT!0=10245. This guidebook contains benchmarking results from selected Wisconsin
wastewater facilities, best practice approaches to on-going management of energy use, best
practice funding and financing opportunities, and references for further opportunities in
water/wastewater system energy efficiency and power demand reduction.
2.6 References
California Energy Commission (CEC). 2000. How to Finance Public Sector Energy Efficiency Projects.
January 2000. Available online at http://www.energy.ca.gov/reports/efficiencv handbooks/400-00-
001A.PDF
Cantwell, J., J. Newton, T. Jenkins, P. Cavagnaro, and C. Kalwara. 2009. Running an Energy-Efficient
Wastewater Utility Modifications That Can Improve Your Bottom Line. WEF Webcast. June 19, 2009.
Evaluation of Energy Conservation Measures 2-7 September 2010
-------
Energy Star. 2010. Energy Star Guidelines for Energy Management. U.S. Environmental Protection
Agency and the U.S. Department of Energy. Accessed 1 March 2010.
http://www.energystar.gov/index.cfm?c=guidelines.guidelines index
EPRI. 1998. Quality Energy Efficiency Retrofits for Wastewater Systems. Electric Power Research
Institute. Project Manager: Keith Cams. CR-109081.
Focus on Energy. 2006. Water and Wastewater Energy Best Practice Guidebook. Report prepared by
Science Applications International Corporation. Available online if requested at
http://www.focusonenergy.com/Business/lndustrial-Business/Guidebooks/
Ishida, C, E. Garvey, S. Dent, S. Deslauriers, and H.S. McDonald. 2008. Optimo: An Innovative
Wastewater Master Plan Optimization Model That Improves System Efficiency, Reduces Risks, and Saves
Capital and O&M Costs. Presented at Utility and Management 2008. Tampa, FL WEF.
USDOE. 2007. MotorMaster+: Motor-Driven Systems, version 4.0.6. U.S. Department of Energy.
http://wwwl.eere.energy.gov/industrv/bestpractices/software motormaster.html
USDOE. 2008. Pumping System Assessment Tool (PSAT). U.S. Department of Energy.
http://wwwl.eere.energy.gov/industry/bestpractices/software psat.html
USEPA. 2006. Wastewater Management Fact Sheet: Energy Conservation. July 2006. EPA Office of Water
832-F-06-024. Available online: http://www.epa.gov/owm/mtb/energycon fasht final.pdf
USEPA. 2008a. Ensuring a Sustainable Future: An Energy Management Guidebook for Wastewater and
Water Utilities. January 2008. Available online:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook si energymanagement.pdf
USEPA. 2008b. EPA Environmental Management Systems: Basic Information. Last updated 17 June
2008. Available online: http://www.peercenter.net/toolkit/
WEF and ASCE. 2010. Design of Municipal Wastewater Treatment Plants - WEF Manual of Practice 8 and
ASCE Manuals and Reports on Engineering Practice No. 76, 5th Ed. Water Environment Federation,
Alexandria, VA, and American Society of Civil Engineers Environment & Water Resources Institute,
Reston, Va.
WEF. 2009. MOP No. 32: Energy Conservation in Water and Wastewater Facilities. Prepared by the
Energy Conservation in Water and Wastewater Treatment Facilities Task Force of the Water
Environment Federation. McGraw Hill, New York.
WERF. 2009. Best Practices for Sustainable Wastewater Treatment: Initial Case Study Incorporating
European Experience and Evaluation Tool Concept. Alexandria, VA: WERF. Available online:
http://www.werf.org/AM/Template.cfm?Section=Search&Template=/CustomSource/Research/Publicati
onProfile.cfm&id=OWSO4R07a
Evaluation of Energy Conservation Measures 2-8 September 2010
-------
3. Energy Conservation Measures for Pumping Systems
Chapter 3 covers:
3.1 Introduction
3.2 Pumping System Design
3.3 Motors
3.4 Power Factor
3.5 Variable Frequency Drives (VFDs)
3.6 References
3.1 Introduction
Pumping operations can be a significant energy draw at wastewater treatment plants (WWTPs),
in many cases are second only to aeration. Pumps are used for many applications. At the plant
headworks, they may be used to provide hydraulic head for the treatment processes. Within the plant,
they are used to recycle and convey waste flows, solids, and treated effluent to and from a variety of
treatment processes. Pumps are also found in remote locations in the collection system to help convey
wastewater to the plant.
The overall efficiency of a pumping system, also called the "wire-to-water" efficiency, is the
product of the efficiency of the pump itself, the motor, and the drive system or method of flow control
employed. Pumps lose efficiency from turbulence, friction, and recirculation within the pump (WEF
2009). Another loss is incurred if the actual operating condition does not match the pump's best
efficiency point (BEP).1 The various methods for controlling flow rate decrease system efficiency.
Throttling valves to reduce the flow rate increases the pumping head, flow control valves burn head
produced by the pump, recirculation expends power with no useful work, and VFDs produce a minor
amount of heat. Of these methods, VFDs are the most flexible and efficient means to control flow
despite the minor heat loss incurred. Table 3-1 summarizes typical pump system efficiency values - note
that inefficiency in more than one component can add up quickly, resulting in a very inefficient pumping
system.
1 BEP is the flow rate (typically in gallons per minute or cubic meters per day) and head (in feet or meters) that gives the
maximum efficiency on a pump curve. For basic information on pump system design, see the WEF Manual of Practice No. 32,
Energy Conservation in Water and Wastewater Facilities (WEF 2009), or the six-part series, Understanding Pump System
Fundamentals for an Energy Efficient World (Pump-Zone 2008 and 2009), available online at http://www.pump-
zone.com/pumps/pumps/understanding-pump-fundamentals-for-an-energy-efficient-world.html
Evaluation of Energy Conservation Measures
3-1
September 2010
-------
Table 3-1. Pump System Efficiency
Pump System
Component
Pump
Flow Control
Motor*
Efficiency of System
Efficiency
Range
30 - 85 %
20 - 98 %
85 - 95 %
Low
30%
20%
85%
5%
Avg
60%
60%
90%
32%
High
75 %n
98%
95%
80%
1. For pumping wastewater. Pump system efficiencies for clean water can be higher.
2. Represents throttling, pump control valves, recirculation and VFDs.
3. Represents nameplate efficiency and varies by horsepower. See Section 3.4 for more information
Inefficiencies in pumping often come from a mismatch between the pump and the system it
serves due to improper pump selection, changes in operating conditions, or the expectation that the
pump will operate over a wide range of conditions. Signs of an inefficient pumping system include:
• Highly or frequently throttled control valves
• Bypass line (recirculation) flow control
• Frequent on/off cycling
• Cavitation noise at the pump or elsewhere in the system
• A hot running motor
• A pump system with no means of measuring flow, pressure, or power consumption
• Inability to produce maximum design flow
For more information, refer to the Pump System Basic Assessment Guide (Pump Systems Matter™
2010), available online at http://www.pumpsystemsmatter.org/content detail.aspx?id=3334.
The literature provides several examples of plants reducing pumping energy by as much as 50
percent through pump system improvements (Focus on Energy 2006). Energy savings result from
lowering of pumping capacity to better match system demands, replacing inefficient pumps, selecting
more efficient motors, and installing variable speed controllers. Generally speaking, energy conservation
measures (ECMs) for pumping are conventional and do not represent an area where recent technology
innovation has played a part in improving energy conservation and efficiency. Pumping ECMs are,
however, still extremely important to reducing and optimizing energy use at wastewater treatment
plants. This chapter provides an overview of conventional ECMs related to pumping design, variable
frequency drives (VFDs), and motors and refers the reader to industry standards and web links for
additional guidance.
Wastewater utilities should consider implementing pumping ECMs as part of a long-term pump
testing and maintenance program. Pumps should be tested every two to three years to ensure that they
are operating efficiently. Utilities should test for flow, head, and power consumption and then calculate
efficiency for each pump system. If overall system efficiency is low (less than 60 or 70 percent for
centrifugal wastewater pumps, less than 72 percent for clean water pumps2), a more detailed evaluation
is warranted. This type of program can give the plant early warning when pump components are failing
and can prevent catastrophic failures. It is important that all components be evaluated and addressed
E-mail communication from Ken Henderson, September 8, 2010.
Evaluation of Energy Conservation Measures
3-2
September 2010
-------
holistically so that the entire system is energy efficient. State and local requirements for redundancy
(e.g., the common requirement that a pump station can pump peak flows with the largest pump out of
service) and safety factors may limit available efficiencies in some cases.
Several tools are available free online to assist wastewater utilities in developing a pump testing
and maintenance program. Pump Systems Matter™, an education program conceived by the Hydraulic
Institute, provides technical references, downloadable tools, tip sheets, and white papers on their
website at http://www.pumpsystemsmatter.org/default.aspx. The Department of Energy (DOE) has
developed and supports the Pump System Assessment Tool (PSAT), available free online at
http://wwwl.eere.energy.gov/industry/bestpractices/software psat.html, to help users determine the
efficiency of their existing pumping systems and calculate energy and cost savings for upgrades. The
Water Environment Federation (WEF) provides guidance on life cycle costing, operation and
maintenance practices, and measurement equipment in their MOP No. 32 (WEF 2009).
3.2 Pumping System Design
Appropriate sizing of pumps is key to efficient operation of wastewater treatment plants. Pumps
sized for peak flow conditions that occur infrequently or, worse, in the future towards the end of the
pump's service life operate the majority of the time at a reduced flow that is below their BEP. Peak flow
is typically several times greater than average daily flow and can be an order of magnitude different
than minimum flow, especially for small systems or systems with significant inflow and infiltration (l&l).
In some systems, these projected future flows are never reached during the design life of the pump.
For existing treatment plants, utilities should evaluate the operation of existing pumps and
identify opportunities for energy reduction. A good starting point is to determine the efficiency of
existing pumping systems, focusing first on pumps that operate for the most hours and have potential
problems as identified by the bullet list in Section 3.1 (presence of bypass lines, throttled valves, etc.).
Plants should collect performance information on the flow rate, pressure, and delivered power to the
pumps. Field measurements may be necessary if the plant does not regularly record this information.
Pump and system curves can then be constructed to determine the actual operating points of the
existing system. Operating points more than 10 percent different than the BEP signal room for
improvement. Detailed guidance on pump system assessment is provided in the Pump Systems Matter
publication, Pump System Basic Assessment Guide, available online at
http://www.pumpsystemsmatter.org/content detail.aspx?id=3334
To improve efficiency, utilities should consider replacing or augmenting large capacity pumps
that operate intermittently with smaller capacity pumps that will operate for longer periods and closer
to their BEP. When replacing a pump with a smaller unit, both the horsepower and efficiency change. A
quick way to estimate the annual energy cost savings is to approximate cost before and after the
improvement and determine the difference using the following equation:
Annual Energy Savings ($) = [hpi x LI x 0.746 x hr x EI x C] - [hp2 x L2 x 0.746 x hr x E2 x C] Eq. 3-1
Where:
hpi = horsepower output for the larger capacity pump
hp2 = horsepower output for the smaller capacity pump
L! = load factor of larger capacity pump (percentage of full load / 100 - determined from pump
curve)
Evaluation of Energy Conservation Measures 3-3 September 2010
-------
L2 = load factor of smaller capacity pump (percentage of full load / 100 - determined from pump
curve)
hr = annual operating hours
C = energy (electric power) rate ($ / kWh)
EI = efficiency of the larger capacity pump
E2 = efficiency of the smaller capacity pump
See Example 3-1 for how the Town of Trumbull was able to save more than $1,500 per year by adding a
small pump to one of its existing sewage pumping stations. When applied correctly, replacement of
standard drives with VFDs can also yield significant improvements (see Section 3.3 for additional
discussion).
Example 3-1 Town of Trumbull, CT, Improves Efficiency at Reservoir Avenue Pump Station
BACKGROUND: Wastewater from the Town of Trumbull, in southwestern CT, is collected and
conveyed to a WWTP in Bridgeport via ten sewage pump stations. One of these, the Reservoir Avenue
Pump station, consisting of two 40-hp direct-drive pumps designed to handle an average daily flow of
236 gallons per minute (gpm). Each pump was operated at a reduced speed of 1320 rpm at 50.3 feet
of total dynamic head (TDH) with a duty point of approximately 850 gpm. A bubbler-type level control
system was used to turn the pumps off and on. One pump can handle the entire peak inflow (usually <
800 gpm) with the second pump operating only during peak flow conditions.
ENERGY EFFICIENCY UPGRADES: To reduce energy use, the town installed a new 10-hp pump and
modified the system control scheme. The new pump handles the same volume as the original pump
but operates for a longer time between standby periods. In addition, the speed control was
eliminated and the original pumps, when used, are run at full speed of 1750 rpm. This allowed the
impellers of the original pumps to be trimmed from 11.25 inches in diameter to 10 inches. The
original pumps are used for infrequent peak flows that cannot be handled by the new 10 hp pump.
Under normal operating conditions, the operating point for the new pump is 450 gpm at 40.7 TDH
compared to 850 gpm at 50.3 feet of head for the whole system. Improvements were made to the
lighting and control systems resulting in additional energy savings.
ENERGY SAVINGS: Annual energy savings were 17, 643 kWh from modifying the pumping system.
Total energy savings were 31,875 kWh/yr, or approximately $2600/yr based on a rate of 8C/kWh.
Total implementation costs were $12,000, resulting in a simple payback of 4.6 years.
FOR MORE INFORMATION:
http://wwwl.eere.energy.gov/industry/bestpractices/case study sewage pump.html (USDOE 2005b)
For greenfield plants and/or new pump stations, utilities should consider and plan for staging
upgrades of treatment capacity as part of the design process. For example, multiple pumps can be
specified to meet a future design flow instead of one large pump so that individual pumps can be
installed as needed, say at year zero, year ten, and year twenty. The State of Wisconsin's Focus on
Evaluation of Energy Conservation Measures 3-4 September 2010
-------
Energy best practices guidebook (Focus on Energy 2006) estimates that staging of treatment capacity
can result in energy savings between 10 and 30 percent of total energy consumed by a unit process.
3.3 Motors
The cost of running electric motors can be the largest fraction of a plant's total operating costs.
WEF estimates that electric motors make up 90 percent of the electric energy consumption of a typical
wastewater treatment plant (WEF 2009). Inefficient motors, operation outside of optimal loading
conditions, and mechanical or electrical problems with the motor itself can lead to wasted energy at the
plant and are opportunities for savings.
The percent energy savings resulting from replacing older motors with premium motors is
modest, typically between 4 and 8 percent (NEMA Standard MG-1. 2006). Savings can be higher when
energy audits reveal that existing motors achieve very low efficiencies, or when existing motors are
oversized and/or under loaded. Many plants have coupled motor replacements with upgrades from
fixed speed to variable speed drives for significantly higher energy savings.
In general, upgrading motors is a conventional ECM that has been practiced at wastewater
treatment plants for some time. Because the main focus of this report is innovative rather than
conventional technologies, this section contains only a brief overview of material, and directs the reader
to other publically available websites and references for detailed information. Specifically, Section 3.3.1
describes motor efficiency and summarizes current motor efficiency standards, and Section 3.3.2
provides links to motor management tools and software. The exception to conventional practices is the
emergence of new, ultra-efficiency motors, which are described in Section 3.3.3.
In addition to tools and references identified in subsequent sections, the reader is referred to
the following websites for technical information on motors:
• The U.S. DOE provides extensive information as part of their Motor Challenges Program.
Publications include downloadable books, tip sheets, and fact sheets on technical and economic
topics related to motors. See
http://wwwl.eere.energy.gov/industry/bestpractices/techpubs motors.html for a list of
published material and relevant web links.
• The Consortium for Energy Efficiency (CEE) provides technical material, links, and fact sheets
under its Motors and Motor Systems Industrial Program (http://www.ceel.org/ind/mot-
sys/mtr-ms-main.php3 ).
Evaluation of Energy Conservation Measures 3-5 September 2010
-------
3.3.1 Motor Efficiency and Efficiency Standards
Motor efficiency is a measure of mechanical power output compared to electrical power input,
expressed as a percentage.
Motor efficiency = PjPe Eq. 3-2
Where:
Pm = mechanical power output of the motor in Watts
Pe = electrical power input to the motor in Watts (WEF 2009)
No motor is 100 percent efficient - all motors experience some power loss due to friction, electrical
resistance losses, magnetic core losses, and stray load losses. Smaller motors generally experience
higher losses compared to larger motors.
The United States Congress, in the Energy Policy Act (EPACT) of 1992, set minimum efficiency
standards for various types of electric motors manufactured in or imported to the United States.
Minimum nominal, full-load efficiencies typically range from 80 to 95 percent depending on size (i.e.,
horsepower) and other characteristics. Motors manufactured since 1997 were required to comply with
EPACT standards and to be labeled with a certified efficiency value.
The National Electrical Manufacturers Association (NEMA) premium efficiency standard has
existed since 2001 (NEMA 2006) as a voluntary industry standard and has been widely adopted due to
its power (and thus cost) savings over EPACT 1992 compliance standards. The 2007 Energy Act raised
efficiency standards of motors to NEMA premium efficiency levels and set new standards for motors not
covered by previous legislation. The 2007 act, which comes into force in December 2010, is summarized
online at http://www.motorsmatter.org/resources/gen legislation.html.
Submersible motors are commonly used in wastewater treatment plants. They serve specialized
applications in environments that are not suited for NEMA motors. There is currently no efficiency
standard for submersible motors and their efficiency is less than NEMA motors. Additionally, their
power factor is usually lower. Their selection is usually driven by the application, though some
applications have alternatives that use NEMA motors. Efficiency should be considered in the evaluation
of alternatives in these applications as it affects the life-cycle cost used in the selection process.
Operating efficiency in the field is usually less than the nominal, full-load efficiency identified by
the motor manufacturer. One reason for this is the operating load. As a rule of thumb, most motors are
designed to operate at between 50 and 100 percent of their rated load, with maximum efficiency
occurring at about 75 percent of maximum load. For example, a motor rated for 20 horsepower (hp)
should operate between 10 and 20 hp and would have its best efficiency around 15 hp. Larger motors
can operate with reasonable efficiency at loads down to the 25 percent range (USDOE 1996). Motors
operated outside of the optimal loading lose efficiency. Other factors that reduce efficiency in the field
include power quality (I.e., proper voltage, amps, and frequency) and temperature. Motors that have
been rewound typically are less efficient compared to the original motor.
Accurately determining the efficiency of motors in service at a plant is challenging because there
is no reliable field instrument for measuring mechanical output power. Several methods are available,
however, to approximate motor efficiency. For a summary, see the U.S. Department of Energy fact sheet
Evaluation of Energy Conservation Measures 3-6 September 2010
-------
on the subject (USDOE 2005), available online at
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/estimate motor efficiency motor svstemts
2.pdf. One method is to use field measurements and technical data in the MotorMaster+ software tool
to estimate efficiency. Section 3.3.2 provides additional information on this tool.
3.3.2 Motor Management Programs
Wastewater utilities should consider purchasing new energy efficient premium motors instead
of rewinding older units when replacing equipment and when making major improvements at the plant
(see the text box in this section for additional recommendations). Motor replacement is best done as
part of a plant-wide motor management program. A first step in program development is to create an
inventory of all motors at the plant. The inventory should contain as much information as possible
including manufacturers' specifications, nameplate information, and field measurements such as
voltage, amperage, power factor, and operating speed under typical operating conditions. Following the
data gathering phase, plant managers should conduct a motor replacement analysis to determine which
motors to replace now and which are reasonably efficient and can be replaced in the future or at time of
failure.
When Should Plants Consider Buying New Energy Efficient Motors?
• For new installations
• When purchasing new equipment packages
• When making major modifications to the plant
• Instead of rewinding older, standard efficiency units
• To replace oversized and/or underloaded motors
• As part of a preventive maintenance or energy conservation program
Source: Motor Challenge Fact Sheet: Buying an Energy Efficiency Electric Motor. Available online
at http://wwwl.eere.enerQV.Qov/industrv/bestt3ractices/t3dfs/mc-0382.pdf
A key input to any motor replacement analysis is economics. A simple approach is to calculate
the annual energy savings of the new motor compared to the old unit and determine the payback period
in years (in other words, when will the cumulative energy savings exceed the initial costs). The following
simple equation can be used to determine annual energy savings:
Annual Energy Savings ($) = hp x Lx 0.746 x hr x Cx (Ep- Ee) Eq. 3-3
Where:
hp = horsepower output of motor
L = load factor (percentage of full load / 100)
0.746 = conversion from horsepower to kW units
hr = annual operating hours
C = energy (electric power) rate ($/kWh)
Ee = existing motor efficiency as a percentage
Ep = premium motor efficiency as a percentage
Evaluation of Energy Conservation Measures 3-7 September 2010
-------
Simple payback in years can then be calculated as the new motor cost (capital plus installation)
divided by the annual energy savings. When comparing buying a premium motor instead of rewinding
an existing one, the cost of rewinding the existing motor should be subtracted from the motor cost. Any
cash rebate from your local electric utility or state energy agency should also be subtracted from the
cost of the new motor. When replacing pumps, motors, or control systems, upgrading the electrical
service, wiring, transformers, and other components of the electrical system should be considered in
calculating energy savings and life cycle costs. Utilities should also consider the importance of reliability
and environmental factors when making motor replacement decisions. More robust economic analyses
such as net present value life cycle cost analysis should be considered, especially for large expenditures.
The ENERGY STAR® Cash Flow Opportunity (CFO) calculator is an easy-to-use spreadsheet tool
that can help plant managers calculate simple payback as well as cost of delay, which is the lost
opportunity cost if the project is delayed twelve months or more. The last sheet of the workbook
provides a summary that can be given to senior managers and decision makers to help convince them of
the financial soundness of energy efficiency upgrades. The CFO calculator and other financial tools are
available for free download at http://www.energystar.gov/index.cfm?c=assess value.financial tools.
The task of motor inventory management and replacement analysis is made significantly easier
by publically available software tools. Developed by the DOE Industrial Technologies Program,
MotorMaster+ is a motor selection and management tool, available free online at
http://www.motorsmatter.org/. It includes inventory management features, maintenance logging,
efficiency analysis, savings evaluation, and energy accounting. It includes a catalog of 17,000 motors
from 14 manufacturers, including NEMA Premium® efficiency motors, and motor purchasing
information. In addition to MotorMaster+ software, the sponsors of the Motor Decisions Matter
campaign developed a spreadsheet tool to assist plant managers with motor replacement/repair
decision making. The tool is titled the "1*2*3 Approach to Motor Management" and is available for free
download at http://www.motorsmatter.org/tools/123approach.html.
3.3.3 Innovative and Emerging Technologies
Siemens Energy and Automation in cooperation with the Copper Development Association has
developed "ultra-efficient" copper rotor squirrel cage-type induction AC motors. These motors exceed
NEMA premium full-load efficiency standards by up to 1.4 percent; however, they are only currently
available in outputs up to 20 hp. In addition to using high-conductivity copper rotors in place of
aluminum, the new motors have the following efficiency improvements:
• Optimized rotor and stator design
• Low-friction bearings
• Improved cooling system
• Polyurea-based grease
• Dynamically balanced rotors
• Precision-machined mating surfaces for reduced vibration
The motor's insulation is designed to be compatible with VFD's (USDOE 2008).
The U.S. Department of Energy (USDOE), in cooperation with Baldor Electric Company and other
private partners, is developing a new grade of Ultra-Efficient and Power-Dense Electric Motors, with the
goal of a 15 percent reduction in motor energy loss over NEMA premium motors. For example, if a
Evaluation of Energy Conservation Measures 3-8 September 2010
-------
NEMA premium motor with particular characteristics and output horsepower was 92 percent efficient
and thus had 8 percent loss, this new grade of motor would reduce loss by 0.15* 8% = 1.2 percent, for a
new overall efficiency of 93.2 percent. The new grade of motor will also be 30 percent smaller in volume
and 30 percent lower in weight, leading to decreased motor cost due to lower materials costs (USDOE
2009). For more information, see DOE's website at
http://wwwl.eere.energy.gov/industrv/intensiveprocesses/pdfs/electric motors.pdf.
3.4 Power Factor
Power factor is important because customers whose loads have low power factor require
greater generation capacity than what is actually metered. This imposes a cost on the electric utility
that is not otherwise recovered by the energy and demand charges. There are two types of power that
make up the total or apparent power supplied by the electric utility. Their relationship is shown in
Figure 3-1. The first is the active power. Measured in kW, it is the power used by the equipment to
produce work. The second is the reactive power. This is the power used to create the magnetic field
necessary for induction devices to operate. It is measured in kVARs.
Active Power, kW
Reactive Power, kVAR
Apparent Power, kVAR
Figure 3-1. Vector Relationship of AC Power
Power factor is the ratio of the active power to the apparent power. The power factor of fully
loaded induction motors ranges from 80 to 90 percent depending on the type of motor and the motor's
speed. Power factor deteriorates as the load on the motor decreases. Other electrical devices such as
space heaters and older fluorescent or high discharge lamps also have poor power factor. Treatment
plants have several motors, numerous lamps, and often electric heaters, which, combined, lowers the
facility's overall power factor.
Power factor may be leading or lagging. Voltage and current waveforms are in phase in a
resistive AC circuit. However, reactive loads, such as induction motors, store energy in their magnetic
fields. When this energy gets released back to the circuit it pushes the current and voltage waveforms
out of phase. The current waveform then lags behind the voltage waveform. When the load is
capacitive, the opposite occurs, and the current waveform leads the voltage waveform.
Improving power factor is beneficial as it improves voltage, decreases system losses, frees
capacity to the system, and decreases power costs where fees for poor power factor are billed. Power
factor can be improved by reducing the reactive power component of the circuit. Adding capacitors to
an induction motor is perhaps the most cost effective means to correct power factor as they provide
reactive power. Synchronous motors are an alternative to capacitors for power factor correction.
Synchronous motors can be run at lagging, unity, or leading power factor by controlling their field
excitation. When the field excitation voltage is decreased, the motor runs in lagging power factor. This
condition is called under-excitation. When the field excitation voltage is made equal to the rated
voltage, the motor runs at unity power factor. The motor runs at leading power factor when the field
Evaluation of Energy Conservation Measures 3-9 September 2010
-------
excitation voltage is increased above the rated voltage. This condition is called over-excitation. When
over-excited, they can provide system power factor correction. Synchronous motors above 300 hp and
below 1200 rpm are often less expensive than a comparable induction motor (Thumann and Dunning,
2008).
The feasibility of adding capacitors depends on whether the electric utility charges for low
power factor. Corrective measures are infrequently installed since many electric utilities do not charge
small customers for poor power factor but rather price it into the electrical rates as a cost of business. A
cost evaluation is needed to determine the type of correction equipment to use. The evaluation should
include motor type, motor starter, exciter (for synchronous motors), capacitors and switching devices if
needed, efficiency, and power factor fees (IEEE 1990). Manufacturers should be consulted before
installing capacitors to reduced voltage solid-state starters and VFDs as there can be problems if they
are not properly located and applied.
3.5 Variable Frequency Drives (VFDs)
VFDs are used to vary the speed of a pump to match the flow conditions. They control the
speed of a motor by varying the frequency of the power delivered to the motor. The result is a close
match of the electrical power input to the pump with the hydraulic power needed to pump the water.
As illustrated by the red areas in Figure 3-2, other methods used to control flow expend more electrical
power than the hydraulic power needed. Throttling valves decrease flow by moving the operating point
on the pump's curve to the left. This is achieved by artificially increasing the head against which the
pump works. Bypass control returns a portion of the water pumped back to the suction side of the
pump, which wastes a portion of the energy used to recirculate the water with no useful work.
Stop/start control is indicative of an over-sized pump that pulses to "match" flow. While this achieves
the same amount of work as a smaller pump operating continuously, it does so at a higher power (kW)
demand. VFDs are a proven technology that is more efficient than these control methods and are
ideally suited in situations where the flow rate is highly variable.
Evaluation of Energy Conservation Measures 3-10 September 2010
-------
Variable speed control
Stop/start control
Rate of flow
Throttle control
Rate of flow
Bypass control
Rate of flow
Rate of flow
Wasted
Energy
Required
Energy
Figure 4. Energy consumption
Figure 3-2. Wasted Energy in Alternative Control Schemes Compared to Variable Frequency Drives
Source: provided courtesy of Pump Systems Matter™ and the Hydraulic Institute, Parsippany, NJ
www.PumpSvstemsMatter.org
3.5.1 Energy Savings
VFDs have been used by many wastewater utilities to conserve energy and reduce costs. A
literature review found numerous success stories with energy savings ranging from 70,000 kWh/yr for
smaller WWTPs (i.e. average daily flow of 7-10 mgd) to 2,800,000 kWh/yr for larger WWTPs (i.e. average
daily flow of 80 mgd) (EPRI 1998; Efficiency Partnership 2009; USDOE 2005c). VFDs are now more
available and affordable, and paybacks for VFDs range from six months to five years depending on the
existing level of control and annual hours of operation (Focus on Energy, 2006).
To approximate the potential energy savings, utilities should develop a curve of actual flow in
hourly increments during a day. Using the curve, energy consumed by a constant speed motor and
throttling valve can be estimated and compared to energy consumed by a VFD system that match the
hourly flow rate to power used.
3.5.2 Applications
VFDs can be installed at remote collection system pumping stations, at lift stations, on blowers,
and on oxidation ditch aeration rotor drives. A common application of VFDs is for pumps that experience
a large variation in diurnal flow, such as at wastewater pumping stations. However, if VFDs are not
selected and applied correctly, they can waste energy. Operating below 75% for full load, VFDs can have
very low efficiencies. In selecting a VFD, information should be obtained from the VFD manufacture
showing the efficiency at different turn down rates.
Evaluation of Energy Conservation Measures
3-11
September 2010
-------
VFDs are not applicable in all situations. VFDs may not be effective when a large static head
must be overcome or where there is little variation in the flow rate (WEF 2009). Additionally, some
motors are not suited for use with VFDs. When the drive reduces the frequency to the motor the voltage
decreases. However, the amperage increases which can generate heat. More commonly, voltage spikes
that develop from the non-sinusoidal wave form produced by VFDs can damage motor insulation if not
properly filtered. Conductors within the motor should be properly insulated and the motors should be
capable of dissipating the heat.
3.5.3 VFD Strategies for Wastewater Pumping Stations
VFDs can be costly to install in an existing pump station and require space in the electrical room.
The range of flow, number of pumps, and hours of operation also need to be considered when
evaluating the implementation of VFD control. Although equipping all pumps with VFDs provides
maximum operational flexibility, this can be costly and, in retrofit projects, not always feasible. Often
the rewards of having VFDs can be achieved at less cost with half or as few as one pump being
equipped.
One VFD can be feasible in small stations where two pumps are run in duty/standby mode
because the duty pump runs the majority of the time, reaping the savings with the VFD. In situations
where both pumps are run in the lead/lag mode to cover the range of flow encountered it is usually
beneficial to have both pumps equipped with VFDs. This allows the pumps to alternate the lead position,
which balances their hours, and it simplifies the controls as both pumps can be operated in the same
manner.
In the case of larger stations with three or more pumps of the same size operated in lead/lag
mode, the number of VFDs needed depends on the range of flow and the space available. If one pump
runs the majority of the time with infrequent assistance from the others, then one VFD would likely
suffice. However, if the second pump operates frequently, then at least two VFDs are recommended. In
the two-VFD scenario, when an infrequent peak flow is needed, the third constant-speed pump can
provide the base load while both VFD-driven pumps adjust to meet the demand. Depending on the size
of the pumps, it could be more beneficial to install a smaller pump instead and run it with a VFD. This
maximizes the efficiency of the system because when the large pumps are run, they are near their BEP
without the heat losses generated by VFDs.
Large stations with multiple pumps of different sizes need to be evaluated on a case-by-case
basis. Typically, VFDs are placed on the smaller pumps so that they can be used to fill in the peaks
before another large pump is turned on. The controls are simple and sequencing is easy to maintain
when a pump is down for service. Additionally, the cost is lower as small VFDs are less expensive than
large ones.
It is important to run each pump periodically. Bearings in pumps that sit too long can be
damaged from brinnelling and stuffing boxes can dry out and leak. It is beneficial from an O&M
standpoint to exercise equipped at intervals recommended by the equipment manufacturer to ensure
their reliability when called upon. Energy-wise, it is best to do this during off-peak electric hours such as
morning or on weekends.
Evaluation of Energy Conservation Measures 3-12 September 2010
-------
3.6 References
American Council for an Energy-Efficient Economy. Motor Provisions in the Energy Policy Act of 1992.
http://www.aceee.org/topics/motors/motor-book
Efficiency Partnership. 2009. Water/Wastewater Case Study: South Tahoe Public Utility District. Flex
Your Power. http://www.fypower.org/pdf/CS Water South Tahoe.pdf
EPRI. 1998. Quality Energy Efficiency Retrofits for Wastewater Systems. Electric Power Research
Institute. Project Manager: Keith Cams. CR-109081.
Focus on Energy. 2006. Water and Wastewater Energy Best Practice Guidebook. Report prepared by
Science Applications International Corporation. Available online if requested at
http://www.focusonenergy.com/Business/lndustrial-Business/Guidebooks/
Home, J., J. Cantwell, and L. Fillmore. 2008. A Roadmap to Sustainable Energy Management: Every
Journey Begins With a First Step. WERF Web Seminar. June 4, 2008.
IMS, 2008. NEMA Premium Efficiency Levels Adopted as Federal Motor Efficiency Performance
Standards. Published as a news service by IMS, inc. http://electronics.ihs.com/news/2008/nema-
efficiencv-levels-adopted-federal.htm
Institute of Electrical and Electronic Engineers, Inc (IEEE). 1990. Recommended Practivesfor Electric
Power Distribution for Industrial Plants (IEEE Red Book). ANSI/IEEE Std 141-1986.
National Electrical Manufacturers Association. 2002. Guide for Determining Energy Efficiency for
Distribution Transformers (TP-1). Free download available with account registration at:
http://www.nema.org/stds/tpl.cfm
National Electrical Manufacturers Association. 2006. NEMA Premium: Product Scope and Nominal
Efficiency Levels, including Tables 12-12 and 12-13 from NEMA Standards Publication MG 1-2006.
http://www.nema.org/stds/complimentary-docs/upload/MGlpremium.pdf
National Electrical Manufacturers Association. 2007. Standards for Motors and Generators (MG-1).
Electronic files and hardcopies available for purchase at: http://www.nema.org/stds/mgl.cfm
Pump Systems Matter. 2007. Pump System Basic Assessment Guide. Parsippany, NJ.
http://www.pumpsystemsmatter.org/content detail.aspx?id=3334
Pump Systems Matter. 2010. Getting Started with Pump System Optimization. Downloaded January 29,
2010 from http://www.pumpsystemsmatter.org/content detail.aspx?id=96 .
Thumann, A. and S. Dunning. 2008. Plant Engineers and Managers Guide to Energy Conservation, 9th Ed.
Fairmont Press, New York.
USDOE. 1996. Replacing an Oversized and Underloaded Electric Motor. Office of Energy Efficiency and
Renewable Energy, Industrial Technologies Program, Washington, D.C. Fact Sheet DOE/GO-10096-287.
http://wwwl.eere.energy.gov/industrv/bestpractices/pdfs/mc-2463.pdf
Evaluation of Energy Conservation Measures 3-13 September 2010
-------
USDOE. 1999. Motor Challenge Project Fact Sheet. City of Milford Pump Optimization Project Yields
$96,000 Net Present Value. U.S. Department of Energy, Office of Industrial Technologies Energy
Efficiency and Renewable Energy.
http://wwwl.eere.energy.gov/industrv/bestpractices/pdfs/milford.pdf
USDOE. Buying an Energy-Efficient Electric Motor. Office of Industrial Technologies, Energy Efficiency
and Renewable Energy. DOE/GO-10096-314
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/mc-0382.pdf
USDOE. 2000. Performance Improvements at Wastewater Treatment Plants. Office of Industrial
Technologies, Energy Efficiency and Renewable Energy.
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/fairf.pdf
USDEO 2005a. Motor Systems Tip Sheet #2: Estimating Motor Efficiency in the Field. Industrial
Technologies Program, Energy Efficiency and Renewable Energy. DOE/GO-102005-2021.
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/estimate motor efficiency motor systemts
2.pdf
USDOE. 2005b. Case Study-The Challenge: Improving Sewage Pump System Performance, Town of
Trumbull. U.S. Department of Energy, Energy Efficiency and Renewable Energy.
http://wwwl.eere.energy.gov/industry/bestpractices/case study sewage pump.html
USDOE. 2005c. Onondaga County Department of Water Environment Protection: Process Optimization
Saves Energy at Metropolitan Syracuse Wastewater Treatment Plant. U.S. Department Of Energy, Energy
Efficiency and Renewable Energy.
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/onondaga county.pdf
USDOE. 2008. New Motor Technologies Boost System Efficiency. United States Department of Energy
Industrial Technologies Program. Published in the Summer 2008 issue of Energy Matters
http://wwwl.eere.energv.gov/industrv/bestpractices/energymatters/archives/summer2008.htmltfa284
USDOE. 2009. Ultra-Efficient and Power-Dense Electric Motors. United States Department of Energy,
Energy Efficiency and Renewable Energy Division.
http://wwwl.eere.energy.gov/industrv/intensiveprocesses/pdfs/electric motors.pdf
Washington State University (WSU) Cooperative Extension Energy Program. 2003. MotorMaster+
Version 4.0 User Guide. Developed for the U.S. Department of Energy. Available online at
http://wwwl.eere.energy.gov/industry/bestpractices/pdfs/motormaster user manual.pdf
Water Environment Federation (WEF), 2009. Manual of Practice (MOP) No. 32: Energy Conservation in
Water and Wastewater Facilities. Prepared by the Energy Conservation in Water and Wastewater
Treatment Facilities Task Force of the Water Environment Federation. McGraw Hill, New York.
Evaluation of Energy Conservation Measures 3-14 September 2010
-------
4. Design and Control of Aeration Systems
Chapter 4 covers:
4.1 Introduction
4.2 ECMs for Aeration Systems
4.3 Control of the Aeration Process
4.4 Innovative Control Strategies for Biological Nitrogen
Removal
4.5 References
4.1 Introduction
The aeration process can account for the largest energy demand of any operation at the facility.
Although the demand is site-specific and can vary widely from plant to plant, the fraction of energy used
for aeration ranges from 25 to as much as 60 percent of total plant energy use (WEF 2009). Because of
the high energy use associated with aeration, energy savings can be gained by designing and operating
aeration systems to match, as closely as possible, the actual oxygen demands of the process. Through
improved understanding of the oxygen demands of a particular wastewater and how those demands
fluctuate with time of day and season, wastewater treatment plants (WWTPs) can build flexibility into
their aeration systems so that operation can address real-time demands efficiently.
Section 4.2 in this chapter describes energy conservation measures (ECMs) for aeration systems.
Section 4.3 follows with a discussion of aeration control, including conventional control based on
dissolved oxygen (DO) measurements and innovative control strategies. Innovative and emerging
technologies for control of biological nitrogen removal are discussed in Section 4.4. See Chapter 5 for
innovative ECMs related to new commercially available blower and diffuser equipment.
4.2 ECMs for Aeration Systems
Wastewater is aerated by either bubbling air or high-purity oxygen through it or by mixing it so
that oxygen is transferred through contact with the atmosphere. The two most common types of
aeration systems are diffused aeration and mechanical surface aeration. Hybrid systems that combine
diffused air and mechanical mixing include jet systems, U-tube aerators, and submerged turbine
aerators. For more information on aeration system components and configuration, see Chapter 14 of
Manual of Practice (MOP) No. 8, Design of Municipal Wastewater Treatment Plants (WEF and ASCE
2010), Chapter 2 of MOP No. 32, Energy Conservation in Water and Wastewater Facilities (WEF 2009),
or the EPA Design Manual for Fine Pore Aeration Systems (USEPA 1989).
Energy efficiency of an aeration system depends on several key factors, including:
• Diffuser flux rate: The rate of airflow per unit surface area of the diffuser (e.g., in standard
cubic feet per minute per square foot of diffuser area). A minimum rate is typically required to
uniformly distribute air to diffusers.
Evaluation of Energy Conservation Measures 4-1 September 2010
-------
• Oxygen transfer rate (OTR): The mass of oxygen dissolved in the mixed liquor per unit of time
(e.g., in Ibs/hr). The OTR for clean water as determined by the manufacturer following standard
test protocols is the standard OTR, or SOTR. The oxygen transfer rate under field conditions is
designated by the subscript/(OTRf).
• Oxygen transfer efficiency (OTE): The mass of oxygen transferred to the liquid from the mass of
oxygen supplied, expressed as a percentage. Similar to OTR, the transfer efficiency as
determined by the manufacturer for clean water at a given gas flow rate and power input is
called the standard oxygen transfer efficiency (SOTE). The transfer efficiency for field conditions
is often designated by the subscript/(OTEf).
• Alpha: The ratio of oxygen transfer efficiency in wastewater versus clean water.
• Mixed Liquor DO Concentration: Although not strictly a design factor, one of the most
significant and controllable factors affecting aeration energy efficiency is mixed liquor dissolved
oxygen concentration. The closer the dissolved oxygen concentration is to saturation, the
greater the resistance for dissolved oxygen dissolution and the lower the OTE. See Section 4.3
for guidance on determining the target mixed liquor DO concentration and implementing
automated control.
Designers try to maximize the OTEf under most operating conditions so that the plant will
operate efficiently. OTEf depends on a number of external factors including water temperature and site
elevation. It decreases with increasing concentration of solids and surfactants. Within the basin itself, it
increases from the inlet to the outlet as organic material is biodegraded. It increases with decreasing
flux rate and is generally higher for deeper basins. Although commercially available aeration equipment
has a wide variety of SOTEs, fine-pore diffusers have the highest efficiency compared to any other
diffused air or mechanical aeration system.
There are many different basin configurations and a variety of aeration equipment that can be
used to improve aeration efficiency. No single approach is right for every system. Life-cycle cost
analysis should always be conducted to ensure that ECMs are appropriately factored into the decision
making process.
Overall design of aeration systems and considerations for energy efficiency are well covered in
existing literature (USEPA 1989, WEF and ASCE 2010, WEF 2009). The purpose of this section is to
provide an overview of ECMs that can be incorporated into a new design or as part of a retrofit project
to an existing basin. Sections 4.2.1 and 4.2.2 provide ECMs for diffused air systems and mechanical
aeration, respectively.
4.2.1 ECMs for Diffused Aeration Systems
Diffused aeration systems introduce air below the wastewater surface. Major components of
diffused aeration systems are the air intake system, blowers, the air piping system, diffusers, and
controls. Air intake systems are typically equipped with filters to protect blowers and diffusers from
airborne particulates. Blowers are essentially low pressure, high volume air compressors. Common
types are positive displacement and centrifugal (see Chapter 5 for detailed discussion of blower
equipment). Air piping systems deliver air from blowers to the diffusers. Headless within the air piping
system is typically a small portion (< 10%) of total system pressure (WEF and ASCE 2010). Aeration
Evaluation of Energy Conservation Measures 4-2 September 2010
-------
control systems are key to keeping the aeration system operating efficiently over the system's entire
operating range. Note that control systems are discussed in Section 4.3.
Conventional ECMs for aeration systems include (1) proper sizing of blowers, (2) dedicated
blowers for channel aeration, and (3) configuration of diffusers within a basin. A forth method emerging
is intermittent aeration. Each is discussed separately below.
Proper Sizing of Blowers
There are many blower configurations that can operate efficiently, especially in larger plants. In
general, blower systems should be designed for a minimum 5:1 turndown ratio, meaning that a system
should be capable of operating at 1/5th of its full capacity (Cantwell et al. 2009). Some common
arrangements that provide for efficient blower operation with back-up are to design for four blowers at
33 percent each of design flow, or two blowers at 25 percent each of design flow plus two blowers at 50
percent each of design flow.
Many plants have more capacity in their aeration system than needed because the population
growth projected during the design phase (a factor in designing treatment plant capacity for a 20year
future projected loading) has not yet occurred or will never occur. In other cases, changes in local
industries or aggressive pre-treatment programs may have resulted in decreased organic loading and
reduced aeration requirements. In these situations and others, it may not be possible for the existing
aeration system to operate efficiently to meet the existing load. Using an aeration system to supply
parasitic loads, such as channel air and air lift pumps, further increases the design capacity of the
system. These applications, which typically require lower pressure, can often be more efficiently served
by a smaller blower. Determining the actual process air requirements without parasitic loads enables a
more efficient system to be designed.
The energy savings associated with retrofits to increase blower turndown depends on many
factors including where the plant is within its design life and how closely projected growth matched
actual growth. If the original design was oversized, energy savings can be significant. Several methods
are available to reduce energy use in these situations, such as replacing larger blowers with one or more
smaller units or installing variable frequency drives (VFDs). Inlet throttling may be applicable, depending
on the blower type, to modulate the air flow rate of existing blowers. Example 4-1 shows how one
utility was able to reduce energy use by approximately 1,000,000 kWh/yr by installing smaller blowers.
Evaluation of Energy Conservation Measures 4-3 September 2010
-------
Example 4-1: City of Waukesha, Replaced Existing Blowers with Smaller Units to Improve Efficiency
BACKGROUND: The City of Waukesha is a medium-sized community of approximately 70,000 residents
located 15 miles west of Milwaukee, Wl. The City's conventional activated sludge wastewater
treatment facility treats between 10 and 12 million gallons per day (mgd) and has a design flow of 18.5
mgd. The plant chemically removes phosphorus by adding ferric chloride in a tertiary treatment
process prior to filtration, UV disinfection, and discharge to the Fox River.
The plant's six aeration basins were equipped with ceramic fine-bubble diffusers. Five 700 hp, inlet
throttled centrifugal blowers provided air to the aeration system. Since the original plant design, the
City began aggressively enforcing their industrial pretreatment program. In addition, some industries
closed or moved out. The combined effect was a significant reduction in organic loading to the plant.
With just one blower running, dissolved oxygen concentrations were high, between 4.5 and 8.0
milligrams per liter (mg/L). The facility could not achieve sufficient turndown of the blower prior to
implementing energy efficiency improvements.
ENERGY EFFICIENCY UPGRADES: In July 2003, the plant replaced two 700 hp blowers with two 350 hp
blowers so that they could operate at a lower DO concentration. They also upgraded their DO probes
with new membrane units and replaced the existing single loop PID DO control system with an
integrated direct flow control system with most open valve control (MOV) logic. During the upgrade,
they took three of the six basins out of service.
ENERGY SAVINGS: Total energy savings from the blower replacement were substantial at
approximately 1,000,000 kWh per year (approximately 9 % of total plant energy use) with an
associated annual energy cost savings of more than $65,000. Total implementation costs were
$approximately $200,000, resulting in a simple payback of about three years.
SOURCE: Cantwelletal. 2009
Dedicated Blowers for Channel Aeration or Air Lift Pumps
The air for channel aeration or air lift pumps processes is often tapped from the main aeration
system air header. However, particularly for channel aeration, the pressure required is significantly
lower than the main aeration system pressure. This excess pressure is usually reduced by throttling the
air through a flow control valve. By providing a small blower rated at the specific pressure required for
the service, the energy requirement can be reduced. This approach is usually viable only for large plants
as the payback period to implement it in smaller plants is usually too long to make the change feasible.
Configuration of Diffusers
The configuration of diffusers within an aeration basin should allow for maximum operational
flexibility to respond to varied conditions and treatment goals. It is also important that their layout
promotes plug flow within the basin and reduces short-circuiting. A common approach is to use tapered
aeration to reduce the rate of oxygen supply along the length of a basin (WEF and ASCE 2010). It can be
accomplished by placing more diffusers at the inlet to the basin where the organic loading is highest and
Evaluation of Energy Conservation Measures 4-4 September 2010
-------
decreasing the number of the diff users along the basin's length. Tapered aeration better matches the
oxygen demand across the basin by providing more air to the head of the basin where it is needed and
less air near the end of the basin where the food-to-microorganisms (F/M) ratio is lower, thereby saving
energy.
If an existing aeration system is under-performing, utilities should examine the configuration of
diffusers to identify possible causes and potential improvements. Changes in number of diffusers and
diffuser configuration could lead to increased energy efficiency. For example, the Waco Metropolitan
Area Regional Sewer System (WMARSS) treatment facility in Waco, Texas was not meeting its
nitrification goals with the plant's existing fine bubble aeration system. An analysis of the facility
operations revealed that the aeration system was being operated in excess of the diffusers' maximum
airflow rate, producing coarse bubbles instead of fine bubbles, which reduced the oxygen transfer
efficiency. The analysis also concluded that additional diffusers were required to effect nitrification.
The utility installed 700 additional diffusers in each of the plant's five aeration basins, bringing the total
number of diffusers in each basin to 3,500. This modification, along with the implementation of
automated DO control, has reduced energy consumption by an average of 4,643,000 kWh per year (an
average 33% reduction) and had a payback period of less than three years. See the case study summary
in Chapter 8 and the full case study with detailed energy and cost information in Appendix A for more
information.
Intermittent Aeration
Intermittent aeration saves energy by reducing the number of hours that an aeration system
operates or the aeration system capacity. It is not appropriate for all facilities, especially those at or
near capacity, and needs to be evaluated on a case-by-case basis so as not to adversely impact the
treatment process. The methodology involves momentarily stopping air flow to an aeration zone or
cycling air flow from zone to zone. The cycle length can be controlled with DO concentration or can be
strictly time based. When controlling with the DO concentration, air flow is turned off at a set high level
and turned back on based on a lower limit. The cycle length on time-based systems is strictly controlled
by a set maximum time. Many basins are limited by mixing, which must be considered when setting the
maximum length of time that the air can be turned off. Additionally, settling of solids within the basin
should be factored in the cycle length.
4.2.2 ECMs for Mechanical Aerators
Mechanical surface aerators vigorously agitate the wastewater, transferring oxygen from the air
by increasing the water-atmosphere interface. Common types of equipment include low-speed
mechanical aerators, direct drive surface aerators, and brush-type surface aerators. Slow speed
mechanical aerators are used in both pond systems and in the activated sludge process. In ponds, they
are mounted on floats and held in position using guy wires. Mechanical aerators are mounted above
the wastewater on a platform in the middle of aeration basins. A shaft extends down through the
platform into the tank to mix the wastewater. Brush aerators are used in oxidation ditches where, in
addition to providing mechanical aeration, they impart a horizontal velocity that is needed to keep the
ditches' contents moving and particles in suspension.
In general, ECMs for mechanical aerators are conventional retrofits. One ECM identified in the
literature is the ability to adjust the submergence of fixed mechanical mixers through the use of
adjustable weirs. Oxygen transfer can be improved and energy use is reduced by installing motor-
Evaluation of Energy Conservation Measures 4-5 September 2010
-------
operated weirs that change the submergence of the impeller based on the dissolved oxygen
concentration (WEF 2009). Thus, the submergence of the impeller delivers more or less oxygen in
response to real time conditions, resulting in energy savings. WEF and ASCE (2010) report that, in
general, radial-flow low-speed mechanical aeration systems can provide higher aeration efficiency than
high-speed machines.
Cycling aerators off during night-time hours can be effective in reducing aeration energy use in
pond systems with multiple surface aerators. As the influent load to the plant decreases in the evening,
the DO concentration rises. This is a potential opportunity to decrease surface aeration. Operationally,
it is better to cycle the aerators so that each aerator is only off for a short time before another is put in
service. As ponds come in different shapes and sizes, the number of aerators and determination of
which aerators to turn off must be carefully evaluated on a case-by-case basis to prevent settling and
the generation of odor.
A new development in mechanical aerators is the use of multiple impellers. Single impeller
mechanical aerators are limited in their turn down due to the need to keep the contents of the basin
from settling. A dual impeller aerator by Eimco Water Technologies, shown in Figure 4-1, includes a
lower impeller near the bottom of the basin floor to augment the surface impeller. This provides
additional mixing energy near the floor of the basin, permitting greater power turndown when a VFD is
used and an associated energy savings. Data from full-scale installations were not identified through a
literature review; thus, potential energy savings have not been quantified and this technology remains
classified as an emerging ECM.
Figure 4-1. Eimco Water Technologies Carrousel System Excell Aeratorll
Source: Eimco Water Technologies. Used with permission.
Evaluation of Energy Conservation Measures 4-6 September 2010
-------
4.3 Control of the Aeration Process
Control of the aeration process is critical to efficient operation of wastewater treatment plants
as both over- and under-aeration have detrimental effects. The energy wasted on over-aeration mounts
quickly as the energy expended increases exponentially with increasing DO concentrations. The DO
concentration needed to maintain stable biological activity is site-specific but usually ranges from 1.0 to
2.0 milligrams per liter (mg/L) for activated sludge systems and as low as 1.0 mg/Lfor nitrification. As
noted previously, operating at DO concentrations closer to saturation increases the resistance of
dissolved oxygen to dissolution. This both lowers the oxygen transfer efficiency (OTE) and increases the
energy expended to drive oxygen into solution. In addition to wasting energy, the following operational
problems have been reported in association with excess dissolved oxygen:
• Poor sludge settling
• Increased foam caused by filamentous organisms (can also occur at low DO)
• Negative impacts on the anoxic zone of a biological nitrogen removal system due to high DO
levels in the recycle flow
Under-aeration can lead to underperformance of the activated sludge process, bulking issues, and, in
some cases, issues with struvite (a phosphorus precipitate) formation in sludge processing resulting
from unwanted biological phosphorus removal. The key point is to have good control over dissolved
oxygen levels so that the aeration system supplies only what is needed.
This section presents ECMs for automated DO control including new advances in DO
instrumentation, emerging DO control technologies, and emerging technologies using control
parameters other than DO.
4.3.1 Automated DO Control
Automated control of the aeration process is an important ECM that can save a plant
considerable energy by quickly adjusting to variable conditions within the basin. The oxygen required to
maintain biological processes (i.e., the oxygen demand) within the aeration basin is proportional to
organic and ammonia loading in the influent wastewater. Oxygen demand for aeration, therefore,
follows the same diurnal pattern, dipping in the middle of the night and peaking in the morning and
evening. The ratio of peak to minimum oxygen demand can typically be 2:1 (Cantwell et al. 2009),
although it can be much higher for small systems and resort communities. Intermittent discharge of
ammonia-rich supernatant from sludge dewatering operations can also dramatically increase the oxygen
demand in the basin. Conversely, dilution from stormwaterflow can reduce oxygen needs. In addition
to fluctuating oxygen demand of the wastewater itself, the oxygen transfer efficiency in the basin also
varies in response to changing air and water temperature and other wastewater characteristics such as
concentrations of solids and surfactants.
In the past, wastewater treatment operators took field measurements to determine the DO
concentration in the aeration basins. Based on the results, operational modifications were made (e.g.,
to blowers or aeration system valves) to increase or decrease the oxygen being delivered to the basins
based on target setpoints. This was typically done only a few times (or once) per day and would not
closely reflect diurnal variations in DO demand. In addition, a high safety factor was often applied to
ensure that the DO level did not decrease below the target concentration should the influent
wastewater characteristics change quickly.
Evaluation of Energy Conservation Measures 4-7 September 2010
-------
To more closely match the air delivered to the biological process oxygen demand, utilities now
commonly install automated control systems. Some new blowers come with automated control for
reliable operations and enhanced energy savings (blower technologies are discussed in Chapter 5).
Because energy required increases exponentially as the DO concentration increases, energy savings
from automated DO control can be significant. For example, WEF and ASCE (2006) estimate that tight
control of DO in the aeration process can save a wastewater plant between 10 and 30 percent of total
energy costs. Energy savings will be site specific and are highly dependent on the control system in
place prior to the upgrade to automated process control. WEF (2009) reports that for medium to large
WWTPs, the payback period for installing automated DO control is generally within a few years.
How it Works
Automated DO control systems use real-time dissolved oxygen (DO) concentration readings
from DO probes located within the aeration basins as inputs to a process controller. The process
controller provides control output to the aeration system that responds by adjusting the brush rotor or
blower speed, the position of variable vane diffusers on the blower, and/or the position of the drop-leg
control valves at the basin to deliver the proper amount of air needed to maintain the target DO
concentration. A simple control system might use one DO probe and one target DO concentration for all
aeration basins. A more complex control strategy involves individual DO probes and air header control
valves for each basin and/or stages within each basin. Individual target DO concentrations for each basin
or stage can further increase energy savings.
Major components of an automated DO control system include:
DO Probes. Typical configurations are membrane (most common), galvanic, or new optical
technology (see Section 4.3.1.1 for a detailed discussion). Probes should be installed in each
aeration basin near the center or close to the inlet of a plug-flow basin.
Blower Air Flow Control. The total air flow supplied to the system is controlled by
modulating the air flow rate delivered by the blowers. The control mechanism depends on
the type of blower. Positive displacement blowers can use VFDs to modulate air flow. Air
flow for multi-stage centrifugal blowers is often controlled by inlet throttling; however, VFDs
also can be used to improve efficiency and turndown. New single-stage centrifugal blowers
use variable speed, inlet guide vanes and variable discharge diffusers to modulate flow for
enhanced energy efficiency. See Chapter 5 for more information on blower technology and
air control.
Basin Air Flow Control. The total air flow supplied by the blowers is divided between
multiple aeration tanks and multiple grids in each tank. The air flow in each zone should be
proportional to process demand in each zone. In small facilities, basin air flow control is
often done manually. In larger facilities, automatically controlled air flow valves can be used
to continuously modulate air flow as DO concentrations change. In the largest facilities,
automatic control may also be provided for individual zones. Most Open Valve (MOV)
control can be used to automatically adjust header pressure so as to maintain a most open
valve at an essentially full open position and minimize system pressure and energy.
Evaluation of Energy Conservation Measures 4-8 September 2010
-------
• Process Control System. The aeration system process controllers receive information from
the DO probes, process results (i.e., compares the basin readings to set point(s)), and sends
signals to air control mechanisms to make a change if needed. Most systems are composed
of programmable logic controllers (PLCs), usually networked together by a Supervisory
Control and Data Acquisition System (SCADA). In larger facilities Distributed Control System
(DCS) are sometimes used, combining local controllers and computer-based operator
interface
Automated DO control systems typically use some form of a feedback control loop, whereby
blower and aeration basin air flow rates are manipulated in response to changes in the DO level in the
aeration basin. Control strategies can be very simple, such as an on-off or setpoint control, or complex
based on proprietary algorithms. A common strategy for automated DO control is a cascaded control
system. In the first loop of cascade control, the process controller sends a signal to the basin air flow
control loop based on the DO probe readings in a basin. For example, if the DO reading is below the
target, the controller will require more air into the basin. In some cases, the basin flow control valve is
manipulated directly by the DO control loop. In most cases, a flow meter and separate air flow
controller are provided. In this type of system, the output of the DO control loop is the setpoint for the
airflow controller.
The second loop is established between a pressure transducer on the main header and the
blower system. Pressure in the line will naturally increase or decrease based on modulations of the
basin air flow control valve. If the basin valve is opened, the header pressure will decrease and the
pressure control loop will send a signal to the blower controller to increase blower air flow. That is, the
output of the pressure control loop is the setpoint for the blower air flow controller. Figure 4-2 provides
a schematic of this common control system.
Evaluation of Energy Conservation Measures 4-9 September 2010
-------
BLOWER AIR FLOW
FLOW
SETPOINT
Traditional System
with Pressure
Control
TANK1
Figure 4-2 Common Cascade System for Automated DO Control
Source: Reproduced courtesy of Dresser, Inc.
TANK 2
Recent advances in automated DO control are related to the probes themselves or the control
strategy. Section 4.3.1.1 discusses new DO probe technology. Advanced DO control systems are
presented in Section 4.3.1.2.
4.3.1.1 DO Measurement Equipment
DO can be measured by membrane electrodes, galvanic electrodes, and optical DO technology
(fluorescence or luminescence). Membrane electrodes, historically the most common DO measurement
device, are composed of two metal electrodes separated from a test solution by a membrane. As
oxygen permeates the membrane, the cathode reduces it and creates a potential that can be correlated
to the amount of dissolved oxygen in the system. They are fairly reliable but must be calibrated
frequently, typically monthly or weekly depending on the manufacturer and site conditions. The
membranes must also be replaced fairly frequently (often quarterly but can be more frequently) (WEF
and ASCE 2006). See the text box on the next page for guidelines on diffuser maintenance. This can be
a time-consuming and tedious activity for operators. Galvanic electrodes, such as the proprietary Zullig
probe, apply a galvanic current to measure the oxygen. This type of probe has significantly less
maintenance than membrane-style probes and can obtain a slightly better energy savings as it maintains
its accuracy longer.
Evaluation of Energy Conservation Measures
4-10
September 2010
-------
Calibration and Maintenance on Membrane-Type Dissolved Oxygen Probes
Most DO probes can be field calibrated to match a known DO concentration reading. A laboratory unit
can be used to measure the mixed liquor DO concentration, and this value is entered into the
transmitter using a menu setting. Membrane type DO probes also have an "air calibration" available. In
this method, the clean probe is exposed to air and the transmitter automatically adjusts the display and
output to match the known concentration of oxygen in ambient air.
In mixed liquor, all types of DO probes can accumulate deposits of biological growth or grease. These
deposits cause inaccuracy in the DO concentration measurement. Frequency of cleaning varies from
once per week to once per month depending on site conditions. Cleaning of most DO probes is
accomplished by removing the probe from the mixed liquor and wiping it with a damp cloth. In
installations with a large number of DO probes, utilities should consider the use of self-cleaning probes.
These employ air blasts, water spray, or mechanical wipers to periodically and automatically remove
deposits from the face of the probe.1
The newest technology on the market, the optical DO probe, measures changes in light emitted
by a luminescent or fluorescent chemical and relates the rates of change in the emission to the DO
concentration in solution. They work on the principle that DO quenches both the intensity and duration
of the luminescence or fluorescence associated with certain chemical dyes (see Figure 4-3 for a
depiction of sensor operation). Thus, the duration of the dye luminescence or fluorescence is inversely
proportional to the dissolved oxygen concentration. Several manufacturers offer optical DO probes
including Hach, Orion, YSI, Insite IG, Endress and Mauser, and Analytical Technologies, Inc.
1 E-mail communication from Tom Jenkins, August 4, 2010.
Evaluation of Energy Conservation Measures 4-11 September 2010
-------
FLUORESCENT
DYE ELEMENT
Figure 4-3. Optical DO Sensor Operation
Source: Analytical Technology, Inc. Brochure Optical Sensor Reduces Maintenance Costs Model for Q45 Optical
Dissolved Oxygen Monitor. Used with permission
The optical DO probe has several advantages over the traditional membrane probe that make it
a good candidate for automated DO control systems. The optical DO probe does not consume
electrolyte and requires less frequent calibration There are no membranes to replace, so maintenance
requirements are low with only the sensor cap requiring replacement approximately once per year (WEF
and ASCE 2006). Accuracy and reliability are also generally greater for the optical DO probe compared
to the membrane probe.
Using optical DO probes instead of traditional membrane probes in automated DO control
systems is not considered an ECM itself; however, a more reliable and easy to use instrument could
pave the way for increased automated DO control installations. For example, Brogdon et al. (2008)
reports on energy savings realized by a Tennessee Valley Authority (TVA) demonstration project to
advance the use of optical DO probes and variable speed drives for automated DO control among small
to medium size utilities. Energy savings associated with the projects ranged from 14 to 40 percent.
Upgrading a system with optical DO probes is often combined with other aeration system
upgrades to ensure reliable operation. For example, the Bartlett Wastewater Treatment Plant #1 in
Tennessee implemented VFD control on one of the two operating rotors in each of the plant's oxidation
ditches using DO readings from optical probes. Prior to implementing this modification, one rotor in
each ditch was operated at constant full speed and the second rotor in each ditch was manually
Evaluation of Energy Conservation Measures
4-12
September 2010
-------
activated during peak flow periods. Following implementation of the ECM, the need to run the second
rotor during peak flow conditions was eliminated. The ECM reduced total plant electrical energy use by
approximately 13 percent and saved the utility more than $9,000 per year. A case study of the Bartlett
ECM project is presented in Appendix A.
4.3.1.2 Advances in DO Control Strategies
Although automated DO control is a significant improvement over manual control, it has some
limitations. It takes time for the DO concentration in the basin to change in response to a change in
organic or ammonia loading (at least a few minutes but it can be much longer). It also takes time for the
process to reach equilibrium after the airflow is increased or decreased. This can cause the valve
position to repeatedly open and close before DO in the basin has stabilized. For example, an increase in
airflow could overshoot the DO target, causing a second manipulation of valve position and airflow rate
to reach the target. Repeated adjustments to find the DO setpoint is commonly referred to as
"hunting." Operators tune the control system to reduce hunting; however, conservative tuning can
make the system unresponsive to changes within the basin. Tuning is made all the more challenging by
the non-linear relationship between DO concentration and air flow to the basin.
New advances in DO control algorithms attempt to address these issues. Two proprietary ECMs
that are emerging for automated DO control are discussed in this section: integrated air flow control and
automated SRT/DO control. Also provided is a description of the most-open-valve control methodology.
Alternatives to DO-based control are discussed in Section 4.3.2.
Most Open Valve (MOV) Control
The goal of MOV control is to avoid excessive throttling on the discharge side of the blowers
since it is not energy efficient to build pressure and then waste it across throttling valves. The amount
of throttling should be limited to what is required to properly split the air flow. This is accomplished by
ensuring the control butterfly valve serving the zone with the highest oxygen demand is essentially full
open.
MOV is now commonly integrated into new aeration control systems. It may not be cost-
effective as an add-on to an existing control system, but utilities should consider specifying for it when
upgrading blowers or aeration controls.
Integrated Air Flow Control
Integrated Air Flow Control is a proprietary aeration control system that was developed by
ESCOR (Energy Strategies Corporation, now part of Dresser, Inc.) that eliminates the pressure control
loop common in many automatic DO control systems. Particularly in smaller systems, the pressure
control loop can cause instability in the operation of the blowers and control valves (cyclic oscillation, or
hunting) as the control system attempts to adjust air flow and pressure in response to changes in the
process and ambient air conditions.
Full-scale implementation of Integrated Air Flow Control has resulted in better stability and
simplified tuning of the aeration process leading to more efficient blower operation. The Narragansett
Bay (Rl) Commission's Bucklin Point facility implemented an ESCOR aeration control system following an
upgrade of their 46 mgd facility in 2005. As part of the upgrade, the aeration system was reconfigured to
Evaluation of Energy Conservation Measures 4-13 September 2010
-------
improve the plant's Modified Ludzack Ettinger (MLE) process to help meet biological nutrient (nitrogen)
removal goals. The upgraded plant, operating with two of the plant's three 600 hp blowers (one in
standby/spare status), had difficulty maintaining consistent nitrogen removal primarily due to
inadequate air supply control. Implementation of the ESCOR Integrated Air Flow Control system, unlike
the system's original pressure-based control system, employs direct flow control of the blowers. As the
DO in the aeration basin varies from setpoint, the required incremental changes in air flow are used to
modify both aeration drop leg air flow and blower air flow. The control system's MOV logic directly
manipulates basin air flow control valve positions to insure that at least one valve is always at maximum
open position, thereby minimizing system pressure without using a pressure control setpoint (See Figure
4-4). The reduced complexity compared to the pressure control system results in more robust and
accurate control and elimination of the pressure control loop minimizes tuning.
BLOWER AIR FLOW
System with
Direct Flow
Control
iTOTAL FLOW SETPOINT
FLOW SETPOINT
Figure 4-4 Integrated Air Flow Control System for Automated DO Control
Source: Reproduced courtesy of Dresser, Inc.
Implementation of the Integrated Air Flow Control provided the required DO control to meet
the plant's total nitrogen discharge requirements and reduced electricity consumption at the facility an
average of approximately 1,247,000 kWh per year (an average reduction of 12%) in the first three years
of operation following commissioning at the end of 2006 (a savings of nearly $136,000). This energy
savings was the result of eliminating the need to constantly run the second of the two plant's blowers.
A case study presentation of the Bucklin Point aeration system control ECM project is provided in
Appendix A.
Automatic SRT/DO Control
DO and sludge age (SRT) are two of the most important operating parameters in activated
sludge treatment. Although reducing DO in the aeration process effects energy savings (i.e., less DO
lowers the energy consumption of the blowers), it often requires increasing SRT to compensate for the
deterioration in process performance. Increasing the sludge age in an activated sludge process,
Evaluation of Energy Conservation Measures
4-14
September 2010
-------
however, can lead to an increase in the sludge settling volume index (SVI), which can increase the plant's
effluent total suspended solids (TSS).
Ekster Associates has developed a proprietary algorithm (OPTIMaster™), based on activated
sludge modeling, plant historical data, and statistical process control that provides setpoint optimization
for sludge age and DO and automates control of these parameters (through automatic sludge wasting
and blower output adjustment) to optimize aeration. The algorithm selects sludge age and a range of
mixed liquor suspended solids (MLSS) and DO concentrations to maintain the proper SVI at minimum
aeration.
Oxnard, CA implemented the OPTIMaster™ system in 2006 and reported a reduction of
approximately 20 percent in the total plant's electrical energy use. A case study presentation of the
Oxnard plant's implementation of the OPTIMaster™ system is provided in Appendix A.
4.3.2 Emerging Technologies Using Control Parameters other than DO
Instead of monitoring and control based on DO concentrations in the aeration basin, another
innovation is to take alternative measurements of biological activity and use this information for process
control. This section describes three emerging ECMs for automated control of the aeration process
using a measurement parameter other than DO: respirometry, critical oxygen point control, and off-gas
monitoring.
Respirometry
Respirometry involves measuring the oxygen uptake rate (OUR) by a biological treatment
culture. In bench-scale respirometry experiments, a sample of mixed liquor representing the biomass in
the aeration basin, possibly amended with an organic substrate or ammonia, is placed in a sealed vessel.
The rate of oxygen consumption within the vessel is monitored overtime. A review of the literature
revealed that online control of aeration using respirometry is possible, but has not been successfully
implemented on a full-scale basis.
Online respirometers also require a representative sample of biomass from the aeration basin.
This source is typically a fresh sample from the mixed liquor, the return activated sludge line, or from an
off-line pilot reactor (Love 2000). The sample is contained in a well-mixed batch reactor or flow-through
system. Oxygen consumption is measured over time (either for the liquid phase or a sealed gas phase).
OUR is based on a mass balance on either the liquid phase or both the gas phase and the liquid and gas
phases within the respirometer. It is important that sufficient oxygen be present in the liquid or gas
phase to prevent oxygen limiting conditions (Love 2000). Figure 4-5 provides an example of a flow-
through respirometric cell.
Evaluation of Energy Conservation Measures 4-15 September 2010
-------
Figure 4-5. Flow-through Respirometry Cell
Source: Strathkelvin Instruments. Used with permission
Online respirometric control has a theoretical advantage over traditional automated DO control.
Whereas DO is essentially an "after-the-fact" analysis once oxygen needs of the biomass have been met,
OUR as measured by a respirometer is a more direct measure of biomass needs and can be used to
predict oxygen requirements for wastewater as it enters the basin. A study at the James C. Kirie Water
Reclamation Plant in Chicago showed that respirometric control is technically feasible using a feed-
forward control strategy (Tata et al. 2000). On-line respirometers were installed in one aeration basin to
determine OUR. Researchers used plant data and literature values to develop two semi-theoretical
mathematical models to predict aeration rate as a function of average basin OUR. Side-by-side
experiments were conducted to compare the plant's existing automated DO control strategy to an
experimental control algorithm based on OUR. Reduced airflow based on the OUR control strategy
caused a reduction in effluent quality, leading Tata et al. (2000) to conclude that even though online
respirometric control is technically feasible, more work would be needed to configure an optimal
control system.
Although respirometry has been used widely in the U.S. to determine kinetics of aerobic
biological processes, online respirometric control of aerobic treatment processes is not common. Trillo
et al. (2004) evaluated the use of respirometry and noted the following limitations:
• Most respirometry analytical devices do not provide true, real-time measurements but rely on
cyclic sampling and analysis.
• The devices require high maintenance because they utilize sampling pumps and require
replenishment of chemical reagents.
Evaluation of Energy Conservation Measures 4-16 September 2010
-------
• The technique requires conditioning of samples or changes in mixed liquor conditions that may
lead to results that are not representative of actual process conditions.
WEF and ASCE (2006) note that the most appropriate applications may be sequencing batch reactors
and oxidation ditches. More commonly, respirometric measurements have been used to create diurnal
load profiles, which are then used as an input to more common DO control strategies.
In 2002, the International Water Association (IWA) published a report titled "Respirometry in
Control of the Activated Sludge Process: Benchmarking Control Strategies" (Copp et al. 2002). This
report contains an evaluation of current control devices and a protocol for evaluating aeration control
strategies using respirometry. The reader is directed to this report for detailed analysis and
recommendations for online respirometric measurement.
Critical Oxygen Point Control Determination
Critical oxygen point control is a control method based on respirometric measurements. The
theory is as follows: bacteria respire by diffusion of oxygen across their cell wall. Oxygen diffuses from a
high concentration external to the bacterial cell wall to the low concentration internal to the bacterial
cell. Diffusion will only take place once the oxygen concentration differential across the cell wall is
sufficient to drive the oxygen through it. The minimum concentration at which this occurs is called the
critical oxygen point. Below the critical oxygen point, the biodegradation rate will rapidly decrease. At
the critical oxygen point, the biodegradation rate will be at a maximum for the available food source
(i.e., organic compounds and ammonia in the wastewater being treated).
Exceeding the critical oxygen point will not materially affect the biodegradation rate. For
carbonaceous bacteria, this critical oxygen point is very distinct. Accurately knowing the critical oxygen
point for the active biomass allows the optimal DO setpoint to be determined.
Strathkelvin Instruments (Scotland, UK) has developed a proprietary software upgrade to their
Strathtox line of respirometers that, in real time, determines the critical oxygen point of the wastewater
under aeration and utilizes this data to change the DO setpoint to control the optimum delivery of
oxygen in the aeration basins. Additional information is available on the manufacturer's webpage at
http://www.strathkelvin.com/waste water/applications.asp.
Off-Gas Analysis
Off-gas testing is a standard test for determining in-process oxygen transfer efficiency (OTE)
based on a gas-phase mass balance of oxygen entering the aeration basin and oxygen leaving the basin
at the wastewater surface. It has been historically used for evaluating aeration system performance,
but has recently received attention as a parameter for aeration system control.
A feed-forward, off-gas monitoring and control system was tested successfully at the Grafton
WWTP in Wisconsin (Trillo et al. 2004). The Grafton WWTP treats 1.1 mgd on average using two parallel
aeration basins equipped with fine pore diffusers. Multistage centrifugal blowers provide the airflow to
the system. The off-gas control system consists of a stainless steel hood for collecting a representative
sample of the aeration system off-gas, a sample conditioning and transport system, gas sensors, and
PLC.
Evaluation of Energy Conservation Measures 4-17 September 2010
-------
In November 2001, the plant began operating the new off-gas control system in one of its two
aeration basins. Trillo et al. (2004) reported the following advantages of the off-gas control system
compared to operation of the conventional feedback-based DO control system:
• Resulted in smaller variations in basin DO (standard deviation of 0.12 mg/L compared to
0.36 mg/L for feedback-based DO control for typical 6-day performance).
• The effluent DO setpoint was reduced from 2.0 mg/L to 1.75 mg/L.
• Recovery time after power loss was reduced by 50 percent.
The authors did not present a side-by-side comparison of energy use for the two treatment trains, but
postulated that the feed-forward off-gas control could reduce energy use by more than 20 percent
compared to conventional feedback-based DO control systems. See Trillo et al. (2004) for additional
information.
4.4 Innovative and Emerging Control Strategies for Biological Nitrogen Removal
The bacteria responsible for biological nitrification (referred to as "nitrifiers" or nitrifying
bacteria) exhibit significant biological diversity. Many can operate at low DO concentrations, particularly
following alternating anoxic and aerobic environments (Littleton et al. 2009). Thus, relying on
automation of DO alone may not result in the most energy efficient system. Although advanced control
of nitrification using multiple measurement parameters such as ammonia and nitrate and nitrite has
been growing overseas, there are still few full-scale applications in the U.S. Still, several proprietary
control systems are on the market and have been tested at full-scale WWTPs. The two described in this
section are the SymBio process and the Bioprocess Intelligent Optimization System (BIOS).
SymBio®
The SymBio® process by Eimco Water Technologies uses online monitoring of nicotinamide
adenine dinucleotide (NADH) to determine changes in biological demands. Based on the results, airflow
to the basin is controlled to promote simultaneous nitrification-denitrification (SNdN) of wastewater.
SNdN refers to a condition in an activated sludge or biofilm process in which the positive bulk liquid DO
concentration is low enough (typically below 1.0 mg/L) that the DO diffusing into the floe is removed
before it can penetrate the entire floe depth. Thus, nitrification is occurring on the exterior portions of
the floe and denitrification is occurring in the anoxic, interior portion, allowing for total nitrogen
removal.
The monitoring device, the NADH sensor, uses a fluorescence sensor to detect changes in NADH
which in turn provides information on the status of biological wastewater treatment processes.
Weerapperuma and de Silva (2004) report that the NADH sensor requires minimal maintenance and can
provide real-time information for process control (article available at:
http://www.eimcowatertechnologies.com/muniusa/index.php?option=com content&view=article&id=
72<emid=146).
The manufacturer claims a 25 to 30 percent energy savings compared to nitrifying plants
without this control technology; however no independent data from full-scale facilities has been
published to verify these claims.
Evaluation of Energy Conservation Measures 4-18 September 2010
-------
Bioprocess Intelligent Optimization System (BIOS)
BIOS is a proprietary control algorithm, on-line process simulation program originally developed
by Biochem Technology, Inc. to optimize the operation of a Modified Ludzack-Ettinger (MLE) biological
nitrogen removal process. Since the de-nitrification and nitrification sections of the MLE process are an
integral part of many other biological nutrient removal processes (e.g., 4- and 5- stage Bardenpho and
A2O processes), the BIOS control system can be applied to other processes having the MLE component.
BIOS is a feed-forward optimization that conducts simulation calculations based upon on-line
measurement of temperature, ammonia, nitrate, and influent wastewater flow rate, integrating these
process measurements with laboratory analytical results for mixed liquor suspended solids (MLSS) as
inputs to the algorithm. The BIOS simulation provides a continuous output of DO setpoints for the
biological treatment process according to the load entering the bioreactor. Additionally, the internal
recirculation flow rate (IRQ) from the aerobic zone to the upstream anoxic zone in the MLE process or
multi-zone BNR process is controlled to achieve optimal total nitrogen removal. Using BIOS to control
the biological nitrogen removal process produces low effluent total nitrogen concentration while
minimizing aeration energy consumption.
Specifically, an ammonia analyzer located in the anoxic zone provides the control system with
the ammonia concentration in the aerobic zone influent and a nitrate analyzer located at the end of the
aerobic zones provides the control system with the nitrate concentration in the internal recycle (IRQ)
stream. BIOS conducts iterative biological and hydraulic simulations that predict the nitrification
reaction rates in the aerobic zones and the de-nitrification reaction rates in anoxic zones under different
DO and IRQ. The simulation iterative calculations take into account that the IRQ will dilute the ammonia
concentration in the anoxic zone and decrease one pass hydraulic retention time in both the anoxic zone
and aerobic zones. As a result, the simulation provides optimal DO set points (for controlling/optimizing
aeration rate) and IRQ (for controlling the process recirculation pump rates) in real-time based on the
changing characteristics of the wastewater. See Figure 4-6 for a diagram of the BIOS process.
NH ~
j^lQ4- Pin's Water & Sludge
T*.™ , F'OW Rate> DO>
i em p. Online Optimization
NH4+/NO.j- ' ** Using Biological & * ¥
Analyzer Hydraulic Models Optimized
4 DO and IRQ
MLVSS
SRT
WAS, Methanol Dosing, etc,
Figure 4-6. Representation of the BIOS process
Source: Lui et al. (2005). Provided courtesy of Biochem Technologies, Inc.
Evaluation of Energy Conservation Measures 4-19 September 2010
-------
4.5 References
American Society of Civil Engineers (ASCE). 1997. ASCE-18-96 Standard Guidelines for In-Process Oxygen
Transfer Testing, American Society of Civil Engineers, New York, NY.
Brogdon, J., C. McEntyre, L Whitehead, and J. Mitchell. 2008. Enhancing the Energy Efficiency of
Wastewater Aeration. Presented at WEFTEC 2008. Chicago, IL WEF.
Cantwell, J., J. Newton, T. Jenkins, P. Cavagnaro, and C. Kalwara. 2009. Running an Energy-Efficient
Wastewater Utility Modifications That Can Improve Your Bottom Line. WEF Webcast. June 19, 2009.
Dooley, M. 2007. Energy Optimization by determination of Critical Oxygen Point in WWTP operations.
Presented at WEFTEC 2007. San Diego, CA. WEF.
Electic Power Research Institute (EPRI). 1998. Quality Energy Efficiency Retrofits for Wastewater
Systems. Electric Power Research Institute. Project Manager: Keith Cams. CR-109081.
Focus on Energy. 2006. Water and Wastewater Energy Best Practice Guidebook. Report prepared by
Science Applications International Corporation. Available online if requested at
http://www.focusonenergy.com/Business/lndustrial-Business/Guidebooks/
Hill, R.D., R.C. Manross, E.V. Davidson, T.M. Palmer, M.C. Ross, S.G. Nutt. 2002. Sensing and Control
Systems: A Review of Municipal and Industrial Experiences. WERF Report 99-WWF-4. WERF.
Alexandria, VA.
Home, J., J. Cantwell, and L. Fillmore. 2008. A Roadmap to Sustainable Energy Management: Every
Journey Begins With a First Step. WERF Web Seminar. June 4, 2008.
Copp, J.B., H. Spanjers, and P. Vanrolleghem. 2002. International Water Association (IWA) Scientific and
Technical Report No. 11: Respirometry in Control of the Activated Sludge Process: Benchmarking Control
Strategies. IWA. Cornwall, UK.
Ekster, et.al. 2007. Forecasting Energy savings Achieved by Automation of Dissolved Oxygen and Sludge
Age Controls and Optimization of Set Points. Presented at WEFTEC 2007. San Diego, CA. WEF.
Larson, L. and M. Stenstrom. 2010. A Digital Control System for Optimal Oxygen Transfer Efficiency.
Prepared by the Southern California Edison and the University of California, Los Angeles. Final Project
Report Published January 2010 by the California Energy Commission. Report CEC-500-2009-076.
Available online at http://www.energv.ca.gov/2009publications/CEC-500-2009-076/CEC-500-2009-
076.PDF.
Littleton, H. X., G. T. Daigger, S. Amad, and P.F. Strom. 2009. Develop Control Strategy to Maximize
Nitrogen Removal and Minimize Operation Cost in Wastewater Treatment by Online Analyzer.
Presented at WEFTEC 2009. Orlando, FL WEF.
Love, N.G. 2000. A review and Needs Survey of Upset Early Warning Devices. WERF Report 99-WWF-2.
WERF. Alexandria, VA.
Evaluation of Energy Conservation Measures 4-20 September 2010
-------
Liu, W., G. Lee, P. Schloth, M.Serra. 2005. Side by Side Comparison Demonstrated a 36 percent Increase
of Nitrogen Removal and 19 Percent of Aeration Requirements Using a Feed Forward Online
Optimization System. Presented at WEFTEC 2005.
Patel, S., O. Jamjun, and S. O'Connell. 2008. Energy Management Techniques and Outcomes at the
Metropolitan Water Reclamation District of Greater Chicago. Presented at Sustainability 2008. National
Harbor, MD. WEF.
Tata, P., K. Patel, S. Soszynski, C. Lue-Hing, K. Cams, and D. Perkins. 2000. Potential for the Use of On-
line Respirometry for the Control of Aeration. Presented at WEFTEC, Anaheim, CA.
Trillo, I., T. Jenkinds, D. Redmon, T. Hilgart, and J. Trillo. 2004. Implementation of Feedforward Aeration
Control Using On-Line Offgas Analysis: The Grafton WWTP Experience. Presented at WEFTEC 2004.
New Orleans, LA.
Shaw, A., A. Fairey, and D. Nolkemper. 2006. Optical Do Sensors Opening Doors to Online Aeration
Control. Presented at WEFTEC 2006. Dallas, TX.
Weerapperuma, D. and V. de Silva. 2004. On-line Analyzer Applications for BNR Control. Presented at
WEFTEC 2004. New Orleans, LA.
Water Environment Federation (WEF). 2008. Manual of Practice (MOP) No. 11: Operation of Municipal
Wastewater Treatment Plants. Water Environment Federation. McGraw Hill, New York.
WEF. 2009. MOP No. 32: Energy Conservation in Water and Wastewater Facilities. Prepared by the
Energy Conservation in Water and Wastewater Treatment Facilities Task Force of the Water
Environment Federation. McGraw Hill, New York.
WEF and The American Society of Civil Engineers (ASCE). 2006. Biological Nutrient Removal (BNR)
Operation in Wastewater Treatment Plants - MOP 29. Water Environment Federation and the American
Society of Civil Engineers. Alexandria, VA: WEFPress.
WEF. 2008. WEF Manual of Practice 11: Operation of Municipal Wastewater Treatment Plants (6th
Edition). WEF and McGraw Hill.
WEF and ASCE. 2010. Design of Municipal Wastewater Treatment Plants - WEF Manual of Practice 8
and ASCE Manuals and Reports on Engineering Practice No. 76, 5th Ed. Water Environment Federation,
Alexandria, VA, and American Society of Civil Engineers Environment & Water Resources Institute,
Reston, Va.
USEPA. 1989. Design Manual: Fine Pore Aeration Systems. Center for Environmental Research
Information, Risk Reduction Engineering Laboratory. EPA/625/1-89/023. Available online at
http://vosemite.epa.gov/water/owrcCatalog.nsf/9da204a4b4406ef885256ae0007a79c7/09b3f5c65174
32e885256b06007233cO!OpenDocument
Evaluation of Energy Conservation Measures 4-21 September 2010
-------
This page left intentionally blank
Evaluation of Energy Conservation Measures 4-22 September 2010
-------
5. Blower and Diffuser Technology for Aeration Systems
Chapter 5 covers:
Introduction and Comparison of Blower Types
High-Speed Gearless (Turbo) Blowers
Single-Stage Centrifugal Blowers with Inlet Guide Vanes
and Variable Diffuser Vanes
New Diffuser Technology
Preventing Diffuser Fouling
References
5.1 Introduction and Comparison of Blower Types
As noted in Chapter 4, the aeration process can account for 25 to as much as 60 percent of total
plant energy use (WEF 2009). This chapter builds on energy conservation measures (ECMs) for aeration
system design and operation presented in Chapter 4 by providing technical information and cost/energy
data for ECMs related to innovative and emerging blowers and diffuser equipment. Note that unlike
other ECMs described in this report, blower and diffuser designs are often unique to manufacturers.
Hence, this chapter contains information on proprietary systems as examples. As noted in the preface,
the mention of trade names, specific vendors, or products does not represent an actual or presumed
endorsement, preference, or acceptance by EPA or the Federal government. The wastewater industry is
constantly evolving and new equipment not identified in this chapter may be available or emerge in the
future. When evaluating new equipment, design engineers and plant owners should work closely with
their state regulatory agency to assess operating principals and potential energy savings.
Blowers are an integral piece of the aeration system. There are many configurations, but all
consist of lobes, impellers, or screws mounted on one or more rotating shafts powered by a motor. As
the shaft turns, the blower pulls in outside air and forces it through distribution pipes into aeration
basins at pressures typically between 5 and 14 pounds per square inch (psi)1. The energy consumption
of blowers is a function of air flow rate, discharge pressure, and equipment efficiency (WEF 2009).
Blower efficiency varies with flow rate, pressure, speed, inlet conditions and actual design.
Blowers can be categorized as either (1) positive displacement blowers, which provide a
constant volume of air at a wide range of discharge pressures, or (2) centrifugal blowers, which provide
a wide range of flow rates over a narrow range of discharge pressure. Centrifugal blowers are either
multi-stage with a sequence of impellers mounted along a single shaft directly connected to a motor
with a flexible coupling, or single-stage with one impeller typically with speed increasing gears or a
variable frequency drive (VFD). Single-stage centrifugal blowers can be conventional integrally geared
blowers or gearless (also known as high speed "turbo") blowers. Positive displacement or centrifugal
blowers (multi-stage or new high speed turbo blowers) are well suited for small plants. Large plants
more often use multi- or single-stage centrifugal blowers as high speed turbo blowers are not yet
available in capacities suitable for large plants. Table 5-1 lists the types of blowers in each category and
provides information on operation, airflow rates, advantages, and disadvantages.
1 Equivalent to psi gauge unless otherwise noted
Evaluation of Energy Conservation Measures 5-1 September 2010
-------
Table 5-1 Overview of Blower Types for Aeration of Wastewater
Category
Positive
Displacement
Centrifugal
Multi-Stage
Centrifugal
Single-Stage
Integrally
Geared
Centrifugal
Single-Stage
Gearless
(High-Speed
Turbo)
Description and
Operation
Provides fixed volume of
air for every shaft
revolution. Operates over
a wide range of discharge
pressures.
Uses a series of impellers
with vanes mounted on
rotating shaft (typically
3,600 rpm). Each
successive impeller
increases discharge
pressure. Individual units
operate at narrow range of
discharge pressures at
wide range of flow rates.
Similar to multi-stage but
uses a single impeller
operating at high speed
(typically 10,000-14,000
rpm) to provide discharge
pressure. Uses gearing
between motor and blower
shaft.
Centrifugal single-stage
blower uses special low-
friction bearings to support
shaft (typically ~ 40,000
rpm). Uses a single or
dual impeller.
Types
Most common
is two counter-
rotating shaft
(rotary) with 2-
or 3-lobed
impellers on
each shaft.
Number of
stages dictates
discharge
pressure
Differences are
in speed and
type of control
(e.g., one or
two sets of
variable vanes)
Magnetic or air
bearing
Typical Air
Flow
Ranges and
Pressures
5-50,000
scfm,
1 - 14 psig
500-30,000
scfm,
4-14 psig,
can be higher
with more
stages
500-70,000
scfm,
4-24 psig
400-10,000
scfm,
4-35 psig
(Manufacturer
s are
currently
expanding
their range of
offerings)
Advantages
• Low capital cost, economical at
small scale
• Can achieve higher output
pressure at same air flow rates
• Simple control scheme for
constant flow applications
• Can be more energy efficient than
positive displacement
• Lower capital cost compared to
single-stage centrifugal blowers
• Can be quieter than single stage
units
• Can be more energy efficient than
multi-stage or positive
displacement
• Can maintain good efficiency at
turndown.
• Typically come with integral
control system for surge protection
• Small footprint
• Efficient technology for lower air
flow capacity ranges
• Can maintain good efficiency at
turndown
• May come with integrated control
systems to modulate flow and for
surge protection
• Can be easy to install (place,
plumb, and plug in)
Disadvantages
• Difficult to operate at variable flow
rates without VFD
• Can be noisy (enclosures are
commonly used for noise control)
• Require more maintenance than
other types
• Typically least energy efficient
• Can be less energy efficient than
single-stage centrifugal
• Efficiency decreases with turndown.
• More moving parts than multi-stage
units. Surge can be more damaging
• Can be noisy (enclosures are
commonly used for noise control)
• Higher capital cost compared to
multi-stage or positive displacement
• Typically higher capital cost
compared to multi-stage or positive
displacement blower (although likely
less expensive than integrally
geared)
• Limited experience (new technology)
• More units required for larger plants
(will change as manufacturers
expand airflow range)
psi = pounds per square inch; scfm = standard cubic feet per minute. VFD = variable frequency drive; rpm = revolutions per minute
Source: WEF 2009; WEF and ASCE 2010
Evaluation of Energy Conservation Measures
5-2
September 2010
-------
Installation costs for blowers depends on a number of factors including atmospheric pressure,
temperature, and humidity of the site location and whether or not units are equipped with various
accessories and controls. Typical cost ranges for a centrifugal multi-stage and turbo blowers as provided
by two blower manufacturers are shown in Table 5-2.
Table 5-2. Manufacturer Cost Ranges for Select Blower Types
Blower Type
Positive Displacement Rotary
Lobe Blower
Positive Displacement Rotary
screw Compressor
Centrifugal Multi-Stage
Centrifugal Single-Stage
Integrally Geared
High Speed Turbo
Range of Discharge Pressure, Flow, and
Horsepower
8 psi and 8,000 scfm, 380 hp^
15 psi at 5,000 scfm, 400 hp2
15 psi at 5,000 scfm, 330 hp^
8 psi and 7,500 - 30,000 cfm, 600 - 2,500 hp
8 psi and 1 ,000 - 7,500 cfm, 50 - 700 hp
8 psi and 100 - 1250 cfm, 3 - 75 hp
12 psi and 4,800 - 6,800 cfm, 200 - 700 hp
12 psi and 6,800 - 10,000 cfm, 250 - 1 ,250 hp
12 psi and 10,000 -22,100 cfm, 600 -2,100 hp
12 psi and 22,400 - 33,200 cfm, 900 - 3,500 hp
8 psi and 2,500 - 8,000 cfm, 200-300 hp
8 psi and 1 ,000 - 2,500 cfm, 75 - 1 50 hp
8 psi and 1 00 - 1 ,000 cfm, 5 - 50 hp
1 0 psi and 600 - 1 ,500 cfm, 30 - 75 hp
1 0 psi and 2,000 - 4000 cfm, 1 00 - 200 hp
10 psi and 5,000 - 8,000 cfm, 250 - 400 hp
10 psi and 10,000 - 15,000 cfm, 500 - 700 hp
ABS, Inc. - 330 HP with Automated Control
System
K-Turbo, Inc. - 50 HP with Automated Control
System
K-Turbo, Inc- 50 HP with Multiple DO Probes
and Integrated Control Systems
Cost Range1
Not provided^
Not provided^
$1 50k to $250kJ
$50kto$150kJ
$35k-$75kJ
$350k - $400ka
$380k - $450ka
$440k - $550ka
$490k - $600ka
$120kto$175kJ
$75kto$120kJ
$35k-$75k"
$50k-$90k"
$115k-$160k"
$180k-$275k"
$325k-$450"
Approximately
$141, 7005
Approximately
$102,0006
Approximately
$56,0007
Notes:
1) Costs are for estimating only - actual equipment cost may vary depending on model, control system, and other specific
requirements. Installation will vary depending on specific project location and site conditions.
2) Information on available models provided by AERZEN USA, 108 Independence Way, Coatesville PA. (contact manufacturer
for cost information at 484-288-6329)
3) Information supplied by HSI, 7901 Hansen, Houston, Texas 77061. Non standard blowers are available in larger sizes
(contact manufacture for details at 713-947-1623)
4) Information supplied by APG-Neuros, Inc., 3200 Cours Le Corbusier, Boisbriand, Quebec, J7JG-3E8, Canada. Non standard
blowers are available in larger sizes (contact manufacture for details at 450-739-0799)
5) Information extracted from the Green Bay, Wl, De Pere WWTP case example in Section 5.2. See Appendix A for full case
study details.
6) Information provided by the Mukilteo Water and Wastewater District.
7) Information extracted from the Burlington, VT, WWTP case example. See Section 5.2 for more details.
8) Information supplied by Atlas Copco Compressors, LLC, 134 Wagon Trail Way, Downingtown, PA 19335. Visit
www.atlascopco.com for more details.
Evaluation of Energy Conservation Measures
5-3
September 2010
-------
Table 5-3 presents typical ranges of isentropic (nominal) energy efficiency and turndown for
different blower types. Note that there is significant variation from small to large blowers of any type;
the values presented are general rules of thumb and may vary with the application.
Table 5-3 Typical Blower Efficiencies
Blower Type
Positive Displacement (variable speed)
Multi-Stage Centrifugal (inlet throttled)
Multi-Stage Centrifugal (variable speed)
Single-Stage Centrifugal, Integrally Geared
(with inlet guide vanes and variable diffuser
vanes)
Single-Stage Centrifugal, Gearless (High-
Speed Turbo)
Nominal Blower
Efficiency (percent)
45-65
50-70
60-70
70-80
70-80
Nominal Turndown
(percent of rated flow)
50
60
50
45
50
Note: values may vary with the application.
Source: Adapted from Gass, J.V. (Black & Veatch) 2009. Used with permission.
Controlling positive displacement blowers is typically done by varying blower speed with a
variable frequency drive (VFD) or use of multiple blowers operating in parallel. Throttling air flow
through the machine is not possible for this type of blower. Multi-stage centrifugal blowers can be
controlled through a variety of techniques, the most efficient being VFDs followed by suction air flow
throttling using inlet butterfly valves. WEF (2009) reports that VFD operation of multi-stage centrifugal
blowers is 15 to 20 percent more efficient than throttling.
This chapter identifies several innovative and emerging ECMs related to blower and diffuser
equipment:
• Turbo blowers are a significant area of innovation in blower design offering energy savings
for the wastewater industry. They emerged in the North American market around 2007 and
have been or are being tested and installed at many plants. Section 5.2 provides detailed
information on turbo blower technology as an innovative ECM, including full-scale plant
data from the literature and case studies.
• Single-stage centrifugal integrally geared blowers are controlled using inlet guide vanes and
variable diffuser vanes. This control technique has the advantages of managing air flow and
pressure independently. See Section 5.3 for discussion of new single-stage centrifugal
blower technology.
• Where fine bubble diffusers were once considered the standard for energy efficiency, new
materials and configurations capable of producing "ultra-fine" bubbles (1 mm or less) are
now available. See Section 5.4 for a discussion of emerging diffuser ECMs.
• Technological advances are also progressing in the area of diffuser cleaning. See Section 5.5
for recommendations for preventing diffuser fouling.
Evaluation of Energy Conservation Measures
5-4
September 2010
-------
A very new technology is the rotary screw compressor. The technology was released to the U.S.
Market in the summer of 2010. The manufacturers claim significant energy savings of up to 50 percent
compared to rotary lobe blower technology. Units are being manufactured by Atlas Copco, AERZEN,
Inc., and Dresser Roots. Because information has only been available for a short while, it was not
possible to conduct a complete evaluation of the technology by industry experts prior to the publication
of this report. For information on the rotary screw compressor technology, the reader is referred to the
manufacturer's website http://www.efficiencvblowers.com/efficiencyblowersus/,
http://www.rootsblower.com/ and https://info.aerzenusa.com.
5.2 High-Speed Gearless (Turbo) Blowers
High-Speed Gearless, or "Turbo," blowers use advanced bearing design to operate at higher
speeds (upwards of 40,000 revolutions per minute [rpm]) with less energy input compared to multi-
stage and positive displacement blowers. Some turbo blowers come in package systems with integrated
VFDs and automated control systems to optimize energy efficiency at turndown.
Turbo blowers are available in two primary configurations based on the manufacturer: (1) air
bearing or (2) magnetic bearing. In an air bearing turbo blower, an air film is formed between the
impeller shaft and its bearings as the shaft rotates at high speed, achieving "friction free" floating of the
shaft. Air bearing technology is offered by several manufacturers including K-Turbo, Neuros, Turblex,
and HSI. In a magnetic bearing design, the impeller shaft is magnetically levitated to provide friction
free floating of the shaft. Turbo blowers featuring magnetic bearing design are offered by ABS Group,
Atlas Copco, and Piller TSC. A magnetic bearing high speed turbo blower is also being developed by
Dresser Roots. Figures 5-1 and 5-2 show features of a common air bearing and magnetic bearing unit,
respectively. The friction free bearing design coupled with high efficiency motors contributes to the
comparative high energy efficiency of the turbo blower technology.
Evaluation of Energy Conservation Measures 5-5 September 2010
-------
Impeller
Highly advanced computational fluid dynamics
Programming allows for performance design
To truly offer an advancement in efficiency
Motor
• Highly efficient and reliable motor design
• Specifically designed forhigh speed service
• Designed for high heat environments
Bearings
AirBearings
• Individually layered bearings are assembled in the housing support shaft
• As the shaft rotates at high speed, an air film is formed between the shaft and the bearings, which achieves friction
free floating without the use of lubricants
• No additional cooling required
• Suitable for high speed; bearing load capability increases with higher RPM
Figure 5-1. Example of High-Speed Turbo Blower with Air Bearings (HSI). Used with permission.
Figure 5-2. Example of High-Speed Turbo Blower with Magnetic Bearings (Atlas Copco) Used with permission.
Evaluation of Energy Conservation Measures
5-6
September 2010
-------
Turbo blowers have many practical advantages (Gass 2009; Jones and Burgess 2009):
• Typically 10 to 20 percent more energy efficient than conventional multi-stage centrifugal or
positive displacement equipment for their current size range based on manufacturers' data.
Good turndown capacity (up to 50 percent) with little drop in efficiency. It is important to
note that efficiencies of turbo blowers at turndown are not yet well documented because
the technology is so new.
• Some include a dynamic control package with integrated variable speed drive, sensors, and
controls that automatically adjust blower output based on real-time dissolved oxygen (DO)
demand in the aeration basin.
• Small footprint and lightweight.
• Quiet, low vibration. Sound enclosures are standard equipment.
• Few moving parts, low maintenance requirements.
Disadvantages of the turbo blower are that it is a new technology with relatively few installations,
capital costs tend to be higher compared to other blower types, and multiple units may be needed for
larger installations. Moreover, testing methods are not consistent among different manufacturers and
some efficiency claims are not yet well documented.
A detailed literature review and input from industry experts identified seven manufacturers of
turbo blowers in the North American wastewater market. Table 5-4 provides a link for each
manufacturer's home page, capacity of available modes, and example installations (if available).
Because turbo blowers are relatively new to the U.S. market, full-scale operating data are
limited. However, detailed cost and operating data have been collected for this report as part of two
facility case studies: (1) Green Bay Metropolitan Sewerage District De Pere WWTP installation of six ABS
magnetic bearing turbo blowers, and (2) The Big Gulch WWTP in Mukilteo, WA installation of three air
bearing turbo blowers by K-Turbo. A summary of the case studies follows Table 5-4. Technical
information and performance data from an installation in Burlington, Vermont follow the case study
summaries.
Evaluation of Energy Conservation Measures 5-7 September 2010
-------
Table 5-4. Examples of Turbo Blower Manufacturers in the North American Market1
Manufacturer
Neuros
K-Turbo
Houston
Services, Inc.
(HSI)
ABS
Atlas Copco
Filler TSC
Dresser Roots
Manufacturer
Web Site
http://www.apq-
neuros.com/
http://www.ktu rbo.c
om/enqlish/main.ht
ml
http://www.hsiblow
ers.com/
http://www.absqrou
p. com/
http://www.atlascop
co.us/usus/
http://www.piller-
tsc.com/index.php?
id=20
http://rootsblower.c
om/
Origin of
Manufacture2
Korea (marketed from
Canada). Substantial
transformation -
manufacturing in US.
Korea (marketed from
Canada). Substantial
transformation -
manufacturing in US.
Korea (assembled in
USA)
Germany (marketed
from UK)
Belgium
Germany
USA
Bearing
Type
Air
Air
Air
Magnetic
Magnetic
Magnetic
Magnetic
Operating Ranges Available
• Flow rates up to 4,500 scfm
• Discharge pressures to 35 psig
• Motor hp from 30 to 300
• Flow rates up to 4,700 cfm for
single impeller, 11,600 cfm for
twin impeller
• Discharge pressures to 21 psig
for single impeller, 28.5 for twin
impeller
• Motor hp from 25 to 600
• Flow rates up to 10,000 scfm
• Discharge pressures to 25 psig
• Motor hp from 5 to 300
• Flow rates up to 10,200 scfm
• Discharge pressures between
5.8 and 12.4 psig
• Motor hp from 400 to 540
• Flow rates up to 3,400 scfm
• Discharge pressures to 22 psig
• Motor hp from 135 to 215 (100
to160kW)
• Flow rates up to 7,000 cfm
• Discharge pressure to 17 psig
• Motor hp to 400 hp
• Flow to 10,000 scfm
• Discharge pressure to 15 psig
Example Installations'3
• Franklin, NH
• Manufacturer claims 108
installations in North America
• First test model began
operation in Oregon in April
2008
• Burlington North Plant in
Vermont 4
• Big Gulch Wastewater
Treatment Plant, Mukilteo,
WA5
• Delphos, OH (to be
commissioned in 2010)
• Essex Junction, VT (to be
commissioned in 2010)
• Green Bay Metropolitan
Sewerage District De Pere
WWTP5
• City of Livermore, CA
None identified
• Nashua, NH
None identified
1. Based on information provided on manufacturer's website as of February 25, 2010. Other manufacturers may be available.
2. Information on substantial transformation is based on results of Buy American waiver applications for the American Reinvestment and Recovery Act
3. Based on literature review and input from technical expert panel and peer reviewers
4. Performance data provided in this section
5. One of nine facility case studies presented in this report. Performance data are summarized in this section. See Chapter 8 for a summary of all case studies and
Appendix A for detailed case study results.
Evaluation of Energy Conservation Measures
5-8
September 2010
-------
Green Bay, Wl, De Pere WWTP (Case Study No. 1)
The Green Bay (Wisconsin) Metropolitan Sewerage District's (GBMSD) De Pere WWTP is a 14
million gallon per day (mgd) two-stage activated sludge plant with biological phosphorus removal and
tertiary effluent filtration. When their existing multi-stage centrifugal blowers reached the end of their
useful life, the District decided to replace the five existing multi-stage units with magnetic bearing turbo
blowers. Six ABS, Inc. HST 330 hp magnetic bearing turbo blowers were installed in October 2004 at a
total capital cost2 of $850,000. The turbo blower project (along with automated controls) saved the
plant more than 2 million kWh per year (a 50 % savings) and $63,758 per year in electrical energy costs.
The project had a simple payback of approximately 13 years. In addition to the energy savings, the new
blowers require significantly less maintenance.
For more information, see the Case Study Summary in Chapter 8 and the detailed facility
assessment including schematics, influent and effluent data, and energy and cost data in Appendix A.
Big Gulch WWTP in Mukilteo, WA (Case Study No. 3)
The Big Gulch WWTP, owned and operated by the Mukilteo Water and Wastewater District, is a
2.6 mgd oxidation ditch plant operating two parallel oxidation ditches. To address increases in BOD and
TSS loadings, the oxidation ditch aeration system has been upgraded as follows:
• The existing mechanical brush (rotor) aeration systems in each ditch were replaced with
Sanitaire fine bubble diffusers and air bearing turbo blowers (three blowers total).
• DO probes with a PLC based control system were installed to automate blower operation.
• A dNOx Anoxic control system was installed to detect the nitrate knee, which is defined as the
point in the nitrogen conversion process where complete denitrification has occurred (i.e., NO3"
has been converted to N2). With the dNOx control system, the blowers are allowed to go idle as
loading increases and automatically switch on when the nitrate knee is detected.
The aeration systems were replaced sequentially with the first ditch (Ditch A) being upgraded in 2008
and second (Ditch B) in 2010.
The total capital and installation cost of the Ditch A upgrade including removal of one rotor
aerator and implementation of one turbo blower, diffusers, air piping, probes, and controls was
$487,066. The Big Gulch WWTP received a $39,191 grant from its electric utility to offset the cost of the
project resulting in a total cost for the Ditch A upgrade of $447,875 dollars. The total capital and
installation cost of the Ditch B upgrade including removal of four rotor aerators and installation of two
turbo blowers, diffusers, air piping, probes, controls and a blower building was $1,045,023. The Big
Gulch WWTP received a $46,594 grant from its electric utility to offset the cost of the project resulting in
a total cost for the Ditch B upgrade of $998,429.
2 The blower replacement project was implemented as part of a larger $2 million plant infrastructure project.
Installation costs related exclusively to the blower implementation are not available. See Appendix A for more
information.
Evaluation of Energy Conservation Measures 5-9 September 2010
-------
The energy savings from the Ditch A aeration system upgrade was 143,940 kWh based on
comparison of energy use in 2009 to average energy use from 2004 through 2008. At the electricity rate
of $0.070 / kWh (in 2009), the resultant electricity cost savings was $10,076. The energy savings from
the combined Ditch A/Ditch B aeration system upgrade was 148,900 kWh for 2010 compared to average
energy use from 2004 through 2008. At the electricity rate of $0.072 / kWh (in 2010), of the resultant
electricity cost savings was $10,721. The simple payback for the entire construction cost of the project
($1,446,304) is more than 135 years.
While the aeration system upgrade project does not meet the case study selection criteria for a
reasonable payback period described in Chapter 1, the project case study is a good example of energy
savings derived as a collateral benefit from a major plant upgrade and expansion. The primary driver of
this project was to increase the plant's capacity to restore permit compliance. Reducing energy
consumption was a secondary consideration. Replacement of the existing mechanical brush aerators in
the oxidation basins with new fine bubble diffusers and turbo blowers did, however, result in overall
energy savings at the facility while accommodating a nearly 40 percent increase in the plant's organic
loading.
If an alternative payback analysis is considered that accounts for the 40 percent increase in the
plant's organic loading during the construction and commissioning of the Ditch A and Ditch B upgrades,
the project shows a significantly lower payback of 33 years. In the year following commissioning of the
total project (2010), the plant removed approximately 34 percent more Carbonaceous Biological Oxygen
Demand (CBOD) compared to the period 2004 through 2008 (prior to the implementation of the
oxidation ditch upgrades) while consuming less electrical power (an average of 1.59 kWh/lb CBOD
during the period 2004 through 2008 compared to an estimated 1.06kWh/lb CBOD in 2010). This
translates to a savings in electricity cost of $0.037 per pound of CBOD removed and an estimated
$43,756 for 2010 (a 33 year payback for the total project cost of $1,446,304).
In addition to improved treatment at lower electric consumption, the Big Gulch WWTP
experienced other benefits from the aeration system improvements. Labor and maintenance costs
decreased because diffusers do not require the level of maintenance required for the mechanical brush
system. The rotor aerators had created aerosol deposits on the railings and equipment which no longer
need to be cleaned with the diffused air system. Chlorine use following the diffused air system is lower
due to improved settling, and the WWTP has eliminated the use of lubrication grease for the aerators.
For more information, see the Case Study Summary in Chapter 8 and the detailed facility assessment
including schematics, influent and effluent data, and energy and cost data in Appendix A.
Burlington, VT
The Burlington Main Wastewater Treatment Plant, located on the eastern shore of Lake
Champlain in Vermont, has a design flow of two mgd but routinely treats approximately one mgd. The
original aeration system was powered by three 75 hp multi-stage centrifugal blowers. The local electric
utility tested one of the blowers and found a relatively consistent power draw of approximately 53 kW.
In July of 2009, the City replaced one existing 75 hp blower with a 50 hp K-Turbo blower and a new
luminescent DO probe for automated control. The installed cost for the blower was approximately
Evaluation of Energy Conservation Measures 5-10 September 2010
-------
$56,000. The City was able to obtain a rebate from the local electric company for $21,000, making the
total project cost only $35,0003.
The new blower has easily met the plant's target DO concentration of 2.5 milligrams per liter
(mg/L) with no operational problems. The Chief Operator reported that the new blower draws between
30 and 70 percent less energy than the original blower. See Figure 5-3 for a comparison of
instantaneous power readings for the new 50 hp turbo blower and power requirements for the replaced
75 hp multi-stage centrifugal blower. Based on operation to date, the estimated total annual energy
savings of the new K-Turbo blower is 250,000 kWh3. This translates to a cost savings of approximately
$34,500 per year based on an average electricity rate of $0.13/kWh and a simple payback of less than 1
year.
Metered Electricity Use of 75 HP
Multi-Stage Centrifugal Blower
(Average Based on Measured Data)
I Instantaneous
Power Draw for 50
HP Kturbo Blower
10 11 12 13 14 15 16 17 IS 19 20 21 22 23 24
Hour (January 25, 2010)
Figure 5-3. Comparison of Power Draw for Old and New Blower at Burlington, VT
Source: Data provided by Tim Grover, Chief Operator for the Main and North Plants, Burlington Department of Public Works,
Burlington, VT on March 1, 2010.
E-mail communication with Tim Grover, Chief Operator, City of Burlington Department of Public Works. March 1
and March 4, 2010
Evaluation of Energy Conservation Measures
5-11
September 2010
-------
5.3 Single-Stage Centrifugal Blowers with Inlet Guide Vanes and Variable Diffuser Vanes
Single-stage centrifugal blowers equipped with inlet guide vanes pre-rotate the intake air before
it enters the high speed blower impellers. This reduces flow more efficiently than throttling. Blowers
that are also equipped with variable outlet vane diffusers have improved control of the output air
volume. Utilizing inlet guide vane and discharge diffusers on a single-stage centrifugal blower makes it
possible to operate the blower at its highest efficiency point, not only at the design condition but also
within a greater range outside of the design condition. PLC control can be used to optimize inlet guide
vane operation (i.e., positioning) based on ambient temperature, differential pressure, and machine
capacity. Automated DO and variable header pressure control can increase efficiency. See Figures 5-4
and 5-5 for example blower configurations and see Figure 5-6 for a picture of the variable outline vane
diffusers.
Figure 5-4. Example of Single-Stage Centrifugal Blower with Inlet Guide Vanes and Variable Diffuser Vanes by
Turblex®. Used with permission.
Evaluation of Energy Conservation Measures
5-12
September 2010
-------
Figure 5-5. Example of Single-Stage Centrifugal Blower with Inlet Guide Vanes and Variable Diffuser Vanes by Dresser
Roots
Source: Dresser, Inc. June 28 2010. Used with permission.
Figure 5-6. Variable Outlet Vane Diffuser from Turblex®. Used with permission.
Single-stage blowers with inlet guide vanes and variable diffuser vanes are currently available
from the following manufacturers: Turblex (owned by Siemens), Dresser Roots, Atlas Copco, and
Howden. Prior to Turblex, single-stage installations were few, largely because there were not many
manufacturers of this technology (most of the Dresser Roots blowers were previously designed for
industrial application).
Although most installations of single-stage blowers with inlet guide vanes and variable diffuser
vanes are relatively new compared to positive displacement and multi-stage blower installations, some
full scale operating data are available. The following is a summary of available data for three full-scale
installations: Oneida, NY; Cape Coral, FL; and Sheboygan, Wl, the latter of which is also the subject of a
detailed facility assessment in Appendix A to this report. Other wastewater utilities that have installed
Evaluation of Energy Conservation Measures
5-13
September 2010
-------
or are planning to install single-stage centrifugal blowers include the City of Rome, NY WWTP (funded
under a performance contract with Johnson Controls), and the City of Conroe, TX WWTP.
City of Oneida, NY
The City of Oneida, located in the geographic center of New York State, operates a 2.5 mgd two-
stage conventional activated sludge WWTP. The city has faced many compliance challenges due to high
wet weather flows, high intermittent BOD loadings from nearby dairy processing plants, regional
growth, and high energy prices. In response to these challenges, the city developed a sustainability
model that began with an energy audit, completed in 2005, to identify energy efficiency measures and a
phased approach to address a long list of projects to improve energy efficiency as well as treatment
capacity and effluent water quality. Phase IB of the project was to install new energy efficient aeration
equipment to replace existing 20-year old multi-stage centrifugal blowers along with replacement of
coarse bubble diffusers with fine bubble diffusers.
The city considered several blower and diffuser choices, basing final selection on a 10-year life
cycle cost analysis. They considered ceramic disk, two tube membranes, and strip membrane diffusers.
While the strip membrane diffusers had the second highest capital costs, they had the lowest net
present value costs and were selected for full-scale installation. The city considered five types of
blowers: three multi-stage centrifugal blowers, one positive displacement blower, and the Turblex
single stage centrifugal blower. Table 5-5 summarizes the City's capital cost analysis of the blowers.
Table 5-5. Net Present Worth of Blower Selections for the City of Oneida (2003$) *
Equipment
Manufacturer (Type)
Continental Blower
(multistage centrifugal)
HSI (multistage centrifugal)
Gardner Denver (multistage
centrifugal)
Turblex (single-stage
centrifugal)
Roots (positive
displacement)
Equipment
Capital Cost
$118,000
$159,600
$158,000
$423,750
$104,800
Annual Energy
Costs
$93,800
$98,900
$104,000
$58,000
$97,200
Net Present
Value
S1.16M
S1.26M
$1.31M
S1.07M
S1.19M
Number of Units and
Horsepower, Air Capacity
for Each
3 operating/1 standby, 100
hp/unit, 1200 scfm/unit
3 operating/1 standby, 100
hp/unit, 1200 scfm/unit
3 operating/1 standby, 100
hp/unit, 1200 scfm/unit
2 operating/1 standby, 100
hp/unit, 2250 scfm/unit
3 operating/1 standby, 75 hp/unit,
1200 scfm/unit
Notes:
1) Assumed 10-year life span, 4% inflation, $0.12/kWh
Source: Greene and Ramer (2007), used with permission of Mark Greene.
Although the Turblex blower's capital cost was nearly three times that of the multi-stage
centrifugal unit and four times the capital cost of the positive displacement blower, the net present
value was the lowest due to the reduction (approximately 40 percent or more) in yearly energy cost
compared to the other blower models. Greene and Ramer (2007) cited turndown rates of 40 percent of
the maximum capacity for the Turblex blower without significant reduction in operating efficiency for
5,000 to 7,000 rpm units.
Evaluation of Energy Conservation Measures
5-14
September 2010
-------
The new blowers and aerators became operational in April 2006. The City of Oneida initially
realized a 49 percent reduction in total plant electrical costs following the installation and start-up of the
new Turblex blowers and fine bubble diffusers. The City was unable to differentiate the energy savings
of the Turblex blowers from the energy savings of switching from coarse bubble to fine bubble diffusers
since both changes were made simultaneously. Note that since 2006, the city has reportedly
experienced operational problems (plugging) of strip diffusers and is replacing them (Greene and Ramer
2007).
Cape Coral, FL
The Everest Parkway Water Reclamation Facility in Cape Coral, FL, has been expanding and
upgrading operations to keep pace with the city's growing population. The plant recently expanded
from a 4-stage biological nutrient removal system to a 5-stage modified Bardenpho system, increased its
capacity from 8.5 mgd to 13.4 mgd, and upgraded and automated its aeration system. As part of this
expansion, the City replaced an older multi-stage centrifugal blower with a single stage 300-hp Turblex
blower. The single-stage blower came on-line in June of 2008 for two of the City's new aeration basins.
The old blower had an annual electricity cost of approximately $96,500 per year, compared to an
expected annual energy cost of $69,700 per year for the Turblex blower, a 28 percent savings. Limited
side by side testing revealed even higher savings. In a 24-hour period, the multi-stage blower consumed
5,089 kWh. The Turblex blower used 2,928 kWh in the same time frame, a 42 percent savings.
For more information, see the article by Doug Day in the March 2010 issue of Treatment Plant
Operators magazine, available online at http://www.tpomag.com/editorial/view/2604/ln-Control (Day
2010).
City ofSheboygan, Wl (Case Study No. 2)
The Sheboygan Regional Wastewater Treatment Plant is an 18 mgd activated sludge plant with
biological phosphorus removal. The plant had been running four 250 hp positive displacement blowers
for the aeration basins. Faced with the need to rebuild existing blowers, plant managers decided to
replace them with two, 350 hp high efficiency motor Turblex centrifugal blowers equipped with inlet
guide vanes and variable diffuser vanes. The capital cost was approximately $504,000 with an
installation cost of approximately $286,000. The plant received a $17,000 energy efficiency grant to
help offset costs, bringing the total costs (capital plus installation minus the grant) to $773,000.
Following commissioning of the Turblex blowers, the plant operators experienced difficulty
controlling DO in the individual aeration basins. DO levels reached 6 mg/L during evening hours
especially in winter months. To correct this problem, air flow control valves were installed on the
headers to each aeration basin along with a programmable logic controller (PLC) for automated control.
The capital cost of the control valve upgrade was approximately $60,000 with an installation cost of
approximately $68,000 for a total cost (capital plus installation) of $128,000.
Measured energy savings from the Turblex blowers was initially low due to DO control
problems. Based on data provided by the Sheboygan WWTP, the average annual energy savings from
2006 through 2008 from the new blowers was 358,000 kWhr/yr (a 13% reduction) with an associated
average cost savings of $25,644. The total annual energy savings in 2009 following the installation of air
flow control valves and automated control was approximately 817,000 kWh/yr (a 30% reduction) with
an associated cost savings of approximately $64,000. If the two projects are taken as a whole, the
Evaluation of Energy Conservation Measures 5-15 September 2010
-------
payback period for the project is 14 years. Although the plant had delayed installing the air control
valves because of cost issues, the absence of control valves limited the ability of the new blowers to
achieve their full potential in energy savings.
For more information, see the Case Study Summary in Chapter 8 and the detailed facility
assessment including schematics, influent and effluent data, and energy and cost data in Appendix A.
5.4 New D iff user Technology
The development of fine bubble diff user technology in the 1970s led to significant reductions in
aeration energy consumption over mechanical and coarse bubble aeration due to the increased oxygen
transfer rates afforded by the high surface area of the fine bubbles. Focus on Energy (2006) estimates
that using fine bubble diffusion can reduce aeration energy from 25 to as high as 75 percent. Estimated
energy savings of 30 to 40 percent are common (USEPA 1999; Cantwell et. al 2009).
There are many different types of fine bubble diffusers available including ceramic/porous
plates, tubular membranes, ceramic disks, ceramic domes, and elastomeric membrane disks, each with
distinct advantages and disadvantages. In general, most diffusers are one of two types: (1) rigid ceramic
material configured in discs or (2) perforated membrane material. Ceramic media diffusers have been in
use for many years and are considered the standard against which new, innovative media are compared.
Membrane diffusers consist of a flexible material with perforated pores through which air is released.
Most often configured in tubes, discs or panels, they comprise the majority of new and retrofit
installations.
Fine bubble aeration has been implemented at many WWTPs and is considered a common
conventional ECM. The focus of this section is ECMs related to new diffuser equipment that can achieve
enhanced energy reduction over fine bubble technology. Note that ECMs related to the configuration of
diffusers within a basin are presented in Chapter 4 of this report.
Recent advances in membrane materials have led to ultra-fine bubble diffusers, which generate
bubbles with an average diameter between 0.2 and 1.0 mm. The primary appeal of ultra-fine bubble
diffusion is improved oxygen transfer efficiency (OTE). Additionally, some composite materials used in
the manufacture of ultra-fine bubble diffusers are claimed to be more resistant to fouling, which serves
to maintain the OTE and reduce the frequency of cleaning. Concerns about ultra-fine bubble diffusion
include slow rise rates and the potential for inadequate mixing. Two proprietary ultra-fine bubble
diffuser designs, panel diffusers by Parkson and Aerostrip® diffusers by the Aerostrip Corporation, are
discussed below.
Panel diffusers are membrane type diffusers built onto a rectangular panel (see Figure 5-7).
They are designed to cover large areas of the basin floor and lay close to the floor. Panel diffusers are
constructed of polyurethane and generate a bubble with a diameter of about one mm. OTE is a function
of floor diffuser coverage, which translates to improved efficiency for panel diffusers. The advantages of
panel diffusers include the increased OTE and the even distribution of aeration. Disadvantages include a
higher capital cost, a higher head loss across the diffuser, increased air filtration requirements, and a
tendency to tear when over-pressurized.
Evaluation of Energy Conservation Measures 5-16 September 2010
-------
Figure 5-7: Ultra-fine Pore Membrane Aeration Panel
Source: Parkson. Used with Permission
AeroStrip® is a proprietary diffuser design manufactured in Austria by Aquaconsult. The device
is a long strip diffuser with a large aspect ratio (Figure 5-8). According to the manufacturer, "...it is a
homogenous thermoplastic membrane held in place by a stainless steel plate." The AeroStrip® diffuser
provides many of the same advantages and disadvantages as panel diffusers; however, it appears to be
less prone to tearing. Also, the smaller strips allow tapering of the diffuser placement to match oxygen
demand across the basin. AeroStrips may be mounted at floor level or on supports above the floor.
Manufacturer's claims regarding the strip membrane diffuser include:
• Energy efficiencies between 10 percent and 20 percent greater than the traditional ceramic
and elastomeric membrane diffuser configurations.
• Uniform bubble release across the membrane surface.
• Bubbles resist coalescing.
• Membrane not prone to clogging.
• Diffusers are self cleaning, although Aerostrip panels have been reported to be susceptible
to frequent fouling requiring bumping and flexing of the membrane to dislodge.4
E-mail communication from David Redmond, July 11, 2010.
Evaluation of Energy Conservation Measures
5-17
September 2010
-------
air connection
base profile
cleaning tap
peripheral clip
membrane
i
/ i
L + 70
Figure 5-8: AeroStrip® Diffusers by the Aerostrip Corporation. Used with permission
Evaluation of Energy Conservation Measures
5-18
September 2010
-------
5.5 Preventing D iff user Fouling
Diffuser fouling can reduce OTE and thereby increase the energy needed to operate the aeration
system. In general, fine bubble diffusers have shown to be more susceptible to fouling than coarse
bubble diffusers. Most require periodic maintenance, and some must be replaced regularly. Ceramic
diffusers require periodic pressure washing or acid cleaning depending on the severity of the fouling.
Pressure washing is often sufficient to remove fouling, including chemical precipitates, and can restore
the diffuser to near-new condition. Occasionally, acid cleaning is needed to remove precipitates.
Intrusion of mixed liquor into the body of ceramic diffuser nearly always necessitates their replacement.
Membrane diffusers attract slime and precipitates. Where slime can be scrubbed off removal of
precipitates require an acid bath.
Some manufacturers of perforated membrane diffusers claim their products are more resistant
to fouling than porous plastic or ceramic diffusers. The susceptibility to fouling is impacted by the
membrane material used. A commonly used membrane material is ethylene propylenediene rubber
(EPDM), which has been shown to be susceptible to biological fouling, while polyurethane or silicone
materials appear to be more resistant (Wagner and Von Hoessle, 2004). New PTFE composite
membranes made by Ott, SSI, and EDI were developed to minimize fouling. However, since these
materials are relatively new, there is insufficient data to support this claim.
Sanitaire® by ITT Water and Wastewater has developed an in-place gas cleaning system that can
be used to clean ceramic fine bubble diffusers without interruption of process or tank dewatering. It
can be added as a retrofit or included as part of new installations. The system is designed to inject
anhydrous HCI gas into the process air stream. At the gas/liquid interface inside the diffusers, the
anhydrous HCL combines with water to form hydrochloric acid. The acid mixture reacts with and
dissolves soluble minerals and removes biological foulants by decreasing the pH. Additional information
from the manufacturer is available online at http://www.sanitaire.com/3117913.asp. Although many
Sanitare® clean-in-place systems exist, their use is limited to existing ceramic diffusers.
A recent publication by Southern California Edison and the University of California, Los Angeles
documents the development of a new monitoring device to help predict cleaning when diffused air
systems require cleaning (Larson 2009). The device measures oxygen transfer efficiency and is
characterized by the study as low-cost ($3,000 - $5,000) and easy-to-use. It is auto-calibrated and does
not require trained experts. Prototype analyzers were installed and tested at a 10 mgd WWTP and plans
are in place to install additional devices at several other plants in California. Larson (2009) estimated an
average energy efficiency improvement of 15 percent with the installation of an on-line analyzer. The
full report is available online at http://www.energv.ca.gov/2009publications/CEC-500-2009-076/CEC-
500-2009-076.PDF.
Evaluation of Energy Conservation Measures 5-19 September 2010
-------
5.6 References
Brogdon, J., C. McEntyre, L Whitehead, and J. Mitchell. 2008. Enhancing the Energy Efficiency of
Wastewater Aeration. Presented at WEFTEC 2008. Chicago, IL WEF.
Cantwell, J., J. Newton, T. Jenkins, P. Cavagnaro, and C. Kalwara. 2009. Running an Energy-Efficient
Wastewater Utility Modifications That Can Improve Your Bottom Line. WEF Webcast. June 19, 2009.
Day, D. 2010. In Control: Automation of a Plant Aeration System in Cape Coral, FL Brings Substantial
Energy Savings and a More Consistent Treatment Process. In Treatment Plant Operator Magazine, Cole
Publishing, Wl. Available online at http://www.tpomag.com/
Electric Power Research Institute (EPRI). 1998. Quality Energy Efficiency Retrofits for Wastewater
Systems. Electric Power Research Institute. Project Manager: Keith Cams. CR-109081.
Focus on Energy. 2006. Water and Wastewater Energy Best Practice Guidebook. Report prepared by
Science Applications International Corporation. Available online if requested at
http://www.focusonenergy.com/Business/lndustrial-Business/Guidebooks/
Home, J., J. Cantwell, and L. Fillmore. 2008. A Roadmap to Sustainable Energy Management: Every
Journey Begins With a First Step. WERF Web Seminar. June 4, 2008.
Jones, T., G. Lapman, and J. Cantwell. 2007. A National Program Initiative to Support Energy Savings in
the Municipal Wastewater Sector. Presented at WEFTEC 2007, San Diego, CA
Jones, T. and J. Burgess. 2009. Municipal Water-Wastewater Breakout Session: High Speed "Turbo"
Blowers. Presented at the Consortium for Energy Efficiency (CEE) Program Meeting. June 3, 2009.
Available online at http://www.ceel.org/cee/mtg/06-09mtg/files/WWWUonesBurgess.pdf.
Gass, J.V. (Black & Veatch). 2009. Scoping the Energy Savings Opportunities in Municipal Wastewater
Treatment. Presented at the CEE Partner's Meeting. September 29, 2009. Available online at
http://www.ceel.org/cee/mtg/09-09mtg/files/WWWGass.pdf.
Greene, M. and D. Ramer. 2007. Innovative Process Modifications Resolve Consent Order and Initiate a
Sustainability Program. Presented at WEFTEC 2007. San Diego, CA. WEF.
Larson, Lory. 2009. A Digital Control System for Optimal Oxygen Transfer Efficiency. California Energy
Commission, PIER Industrial / Agricultural / Water End-Use Energy Efficiency program. Report CEC-500-
2009-076. Available online at http://www.energv.ca.gov/2009publications/CEC-500-2009-076/CEC-500-
2009-076.PDF .
Lawrence and Kim. 2009. The Efficiency Program Perspective on Energy Efficiency in Wastewater
Blowers. Presented at the CEE Partner's Meeting. September 29, 2009. Available online at
http://www.ceel.org/cee/mtg/09-09mtg/files/WWWLawrenceKim.pdf
Littleton, H. X., G. T. Daigger, S. Amad, and P.F. Strom. 2009. Develop Control Strategy to Maximize
Nitrogen Removal and Minimize Operation Cost in Wastewater Treatment by Online Analyzer.
Presented at WEFTEC 2009. Orlando, FL. WEF.
Evaluation of Energy Conservation Measures 5-20 September 2010
-------
Personal Communication with Tim Grover, Chief Operator for the Main and North Wastewater
Treatment Plants, City of Burlington Department of Public Works. March 1, 2010.
Wagner M, von Hoessle R. 2004. Biological Coating of EPDM-membranes of Fine Bubble Diffusers.
Water Science and Technology. 2004; 50(7):79-85.
Wallis-Lage, C.L, E. Whitman, B. Hemken. 2005. Taking Aeration to a New OTE Level. Presented at
WEFTEC 2005, Washington, DC.
Water Environment Federation (WEF). 2008. Manual of Practice (MOP) No. 11: Operation of Municipal
Wastewater Treatment Plants. Water Environment Federation. McGraw Hill, New York.
WEF. 2009. MOP No. 32: Energy Conservation in Water and Wastewater Facilities. Prepared by the
Energy Conservation in Water and Wastewater Treatment Facilities Task Force of the Water
Environment Federation. McGraw Hill, New York.
WEF and the American Society of Civil Engineers (ASCE). 2006. Biological Nutrient Removal (BNR)
Operation in Wastewater Treatment Plants - MOP 29. Water Environment Federation and the American
Society of Civil Engineers. Alexandria, VA: WEFPress.
WEF and ASCE. 2010. Design of Municipal Wastewater Treatment Plants - WEF Manual of Practice 8
and ASCE Manuals and Reports on Engineering Practice No. 76, 5th Ed. Water Environment Federation,
Alexandria, VA, and American Society of Civil Engineers Environment & Water Resources Institute,
Reston, Va.
USEPA. 1989. Design Manual: Fine Pore Aeration Systems. Center for Environmental Research
Information, Risk Reduction Engineering Laboratory. EPA/625/1-89/023. Available online at
http://vosemite.epa.gov/water/owrcCatalog.nsf/9da204a4b4406ef885256ae0007a79c7/09b3f5c65174
32e885256b06007233cO!OpenDocument
USEPA. 1999. Wastewater Technology Fact Sheet: Fine Bubble Aeration. EPA 832-F-99-065. Available
online at http://www.epa.gov/OW-OWM.html/mtb/fine.pdf
Evaluation of Energy Conservation Measures 5-21 September 2010
-------
This page left intentionally blank.
Evaluation of Energy Conservation Measures 5-22 September 2010
-------
6. Innovative and Emerging Energy Conservation Measures for Selected
Treatment Processes
6.1 Introduction
6.2 UV Disinfection
6.3 Membrane Bioreactors (MBRs)
6.4 Anoxic and Anaerobic Zone Mixing
6.5 References
6.1 Introduction
Unlike energy conservation measures (ECMs) for aeration and pumping, ECMs for advanced
treatment technologies such as ultraviolet (UV) disinfection and membrane bioreactors (MBRs), and for
other process functions, such as anoxic zone mixing are emerging and generally not yet supported by
operating data from full-scale installations. They are very important, however, because wastewater
treatment plants (WWTPs) are increasingly employing these technologies. This chapter provides a
discussion of ECMs for advanced technologies and presents full-scale plant test results where available.
Where operation data are not available for manufacturer's information is provided.
6.2 UV Disinfection
Because of concerns related to security, safe handling, and effluent toxicity associated with
chlorine, UV radiation has become increasingly popular over the years as an alternative to chemical
disinfection. Leong et al. (2008) estimated that as of 2007, approximately 21 percent of municipal
WWTPs were using UV for disinfection. That number is only expected to rise as manufacturers continue
to improve UV equipment designs and decrease costs, and as more and more WWTPs gain experience
with the technology.
UV radiation at certain wavelengths (generally between 220 to 320 nanometers [nm]) can
penetrate the cell walls of microorganisms and interfere with their genetic material. This limits the
ability of microorganisms to reproduce and, thus, prevents them from infecting a host. UV radiation is
generated by passing an electrical charge through mercury vapor inside a lamp. Low-pressure, low-
intensity lamps, which are most common at WWTPs, produce most radiation at 253.7 nm. Medium-
pressure high-intensity lamps emit radiation over a much wider spectrum and have 15 to 20 times the
UV intensity of low-pressure low-intensity lamps. Although fewer lamps are required as compared to
low-pressure systems, medium-pressure lamps require more energy.
Components of UV disinfection equipment include the UV lamp (mercury and inert gas inside a
lamp envelope with electrodes on either side to emit a charge), a quartz sleeve around the lamp to
protect it and prevent breakage, a lamp cleaning system, sensors, and a control system. The most
common configuration for wastewater treatment is for open channel flow and modular design (WEF and
ASCE 2010). Lamps are either parallel or perpendicular to the direction of flow and arranged horizontally
or vertically. The perpendicular to flow configuration is more commonly used for wastewater treatment
applications, whereas the parallel to flow configuration is typically used for potable water applications.
Evaluation of Energy Conservation Measures 6-1 September 2010
-------
Some UV systems are manufactured in a closed channel pressure vessel configuration. Figure 6-1 shows
examples of UV lamp designs. For more information on UV disinfection for wastewater, see the USEPA
Technology Fact Sheet on UV disinfection (USEPA 1999), available online at
http://www.epa.gov/OWM/mtb/uv.pdf and Chapter 19 of the Water Environment Federation (WEF)
Manual of Practice (MOP) No. 8, Design of Municipal Wastewater Treatment Plants (WEF and ASCE
2010).
(a)
(b)
(c)
(d)
Figure 6-1. Example UV Lamp Configurations for Wastewater Treatment (a) Calgon C3150 for open channel flow,
horizontal and parallel lamp arrangement (b) TrojanUVFit for closed channel flow (c) TrojanUV4000Plus for open
channel flow, horizontal and parallel lamp arrangement, and (d) Aquaray® 3X Vertical Lamp System for open
channel flow, perpendicular lamp arrangement. Used with permission.
Evaluation of Energy Conservation Measures
6-2
September 2010
-------
Energy requirements for UV depend on the number, type, and configuration of lamps used to
achieve the target UV dose for pathogen inactivation. One of the most important factors affecting UV
dose delivery is UVtransmittance (UVT) of the water being disinfected. UVT is defined as the percent of
light passing through a wastewater sample over a specific distance (1 centimeter). It takes into account
the scattering and adsorption of UV by suspended and dissolved material in the water. UVT is affected
by level of pretreatment - filtered wastewater has a much higher UVT than unfiltered water.
Microorganisms that move quickly through the reactor far from the lamp will receive a lower dose than
microorganisms that have longer exposure to the UV radiation and are closer to the lamp. Other factors
affecting UV dose delivery are temperature, lamp age, and lamp fouling. Because UV disinfection is
complex and based on many factors, dose estimation methods are complicated and typically involve
computational fluid dynamic modeling or bioassays. Dose can be maintained at a minimum level or can
be controlled based on water quality (i.e., lowered during periods of improved quality) which can save
energy.
A study funded by the Pacific Gas and Electric (PG&E) company found that the energy consumed
by UV disinfection can account for approximately 10 to 25 percent of total energy use at a municipal
wastewater treatment facility (PG&E 2001)1. Energy required for low-pressure lamps ranged from
approximately 100 to 250 kilowatt hours (kWh) per million gallons (MG). Energy required for medium-
pressure systems ranged from 460 to 560 kWh/MG, with one plant requiring 1,000 kWh/MG to achieve
a very high level of coliform inactivation. PG&E (2001) reported that UV disinfection performance in
relation to input energy is not linear. An increasing amount of energy is required to obtain marginal
reductions in most probable number (MPN) per milliliter for total coliforms.
ECMs for UV disinfection are fairly new, and energy savings/cost data are not well documented
in the literature. Still, growing experience with UV disinfection has revealed practical design, operation,
and maintenance strategies that can reduce the energy use of UV disinfection. The following sections
summarize these ECMs and provide detailed information on upgrades and associated energy savings for
several WWTPs as reported in the literature.
6.2.1 Design
Pretreatment
Pretreatment to remove suspended solids from wastewater, such as tertiary sand filtration or
membranes, can increase UVT and allow a plant to reach the same level of treatment at a lower UV
dose, thereby saving energy. If a plant uses iron or aluminum compounds for chemical precipitation of
phosphorus, it is important to minimize residual iron and aluminum concentrations to prevent
acceleration of UV lamp fouling (Leong et al. 2008).
Lamp Selection
Medium-pressure lamps require two to four times more energy to operate than low-pressure,
low-intensity lamps. In some cases, WWTPs can save on energy costs by specifying low-pressure low-
intensity lamps. Tradeoffs are (1) a larger footprint for the same disinfection level, which can be
1 Based on a detailed evaluation of seven wastewater treatment plants ranging in flow rate from 0.4 to 43 million
gallons per day (mgd). Data set included plants with low-pressure low-intensity lamps and high-pressure high-
intensity lamps in a variety of configurations.
Evaluation of Energy Conservation Measures 6-3 September 2010
-------
significant because as many as 20 low-pressure low-intensity lamps are needed to produce the same
disinfecting power as one medium-pressure lamp, and (2) higher operating costs for maintenance and
change out of additional lamps.
Low-pressure high-output lamps are similar to low-pressure low-intensity lamps except that a
mercury amalgam is used instead of mercury gas so they can operate at higher internal lamp pressures.
Thus, the UV output of a low-pressure high-output lamp is several times that of a low-pressure low-
output lamp (Leong et al. 2008). Low-pressure high-output lamps have significant advantages of:
• Reducing lamp requirements (i.e., quantity) compared to traditional low-intensity lamps,
and
• Reducing energy requirements compared to medium-pressure lamps.
Leong et al. (2008) reported that the energy demand for low-pressure high-output systems is similar to
that of low-pressure low-intensity systems. Thus, low-pressure high-output lamps may be a good option
for reducing the number of lamps and footprint while keeping the energy requirements low.
Salveson et al. (2009) presented results of a pilot test at the Stockton, CA WWTP comparing
design conditions and operation of medium pressure and low-pressure high-output lamps. Results are
shown in Table 6-1. The power draw for the low-pressure high-output lamps was between 20 and 30
percent of the power draw for the medium pressure lamps, reducing annual O&M costs significantly.
These results are similar to information reported from one manufacturer for a 30 mgd plant treating
secondary effluent. A low-pressure high output system would use 60 kW at peak flow compared to 200
kW for a medium pressure system (Faber 2010).
Table 6-1. Disinfection Equipment Power and Cost Estimates (55 mgd Peak Flow, 38 mgd
Average Flow, 65% Design DVT)
Dose
(mJ/cm2)
50
70
110
Lamp Type
Medium Pressure
Low Pressure High Output
Medium Pressure
Low Pressure High Output
Medium Pressure
Low Pressure High Output
Total No. of
Lamps
216
768
324
1,152
540
1,792
Power
(kW)1
648
143
1,058
219
1,512
415
Annual Energy
Costs2
$681,000
$150,000
$1,120,000
$231,000
$1,589,000
$437,000
Life Cycle
Cost3
$20,427,000
$14,248,000
$31,741,000
$19,726,000
$46,988,000
$30,615,000
1. Power draw is based on operational values (kW).
2. Based on operational values and energy cost of $0.13 per kWh.
3. Life Cycle Cost = 13.01 (20 years annual cost at 4.5% discount rate) * annual O&M cost + project cost
Source: Salveson et al. 2009; Supplemental information provided in e-mail communication to the author from Nitin Goel, March
24, 2010. Used with permission.
System Turn-Down
Similar to the design of blowers for aeration systems, it is important that designers allow for
sufficient UV system turn-down to respond to changes in flow and wastewater quality. Flexibility and
Evaluation of Energy Conservation Measures
6-4
September 2010
-------
control in design is a key factor in operating efficiently from the day the technology is commissioned
until the end of its design life.
The configuration of the lamps dictates the approach for lamp turn-down. In systems with
vertical lamp configurations, the water level can vary during operation (with respect to the submerged
portion of the lamp), whereas in a horizontal lamp configuration, the water levels should remain
relatively constant (with respect to lamp submergence). Individual rows of lamps can be turned on and
off in vertical configurations. In horizontal arrangements, channel control is more typically used to
respond to varying flows (Leong et al. 2008). Regardless of configuration, the number of channels should
be selected to maintain a velocity that has been tested and is known to provide the required dose
delivery.
System Hydraulics to Promote Mixing
As noted previously, UV dose delivery inside a UV reactor depends on the hydraulics. Optimized
longitudinal and axial mixing of the water is critical to maintaining a minimum UV dose throughout the
reactor. In general, this is achieved by operating at a sufficiently high approach velocity to ensure
turbulent flow conditions (WEF and ASCE 2010). WWTPs should conduct full-scale, pilot testing before
installation to ensure that mixing effects are addressed in design. Flow equalization prior to the UV
reactor can also stabilize hydraulic conditions and prevent high or low flows from causing reduced UV
disinfection performance. It is important to note that mixing is a balancing act. Extreme agitation of the
wastewater can create bubbles that shield pathogens from exposure to the UV radiation.
6.2.2 Operation and Maintenance
Automation
Automation can reduce the number of lamps and/or channels operating based on real-time flow
and wastewater characteristic data, thereby reducing energy use and also extending UV lamp life.
Controls can be designed to turn off lamps or divert flow to a few operating channels depending on the
UV system design. Control is most commonly flow-paced control or dose-paced control. Flow-paced is
the simplest with number of lamps/channels in service based strictly on influent flow rate. Dose-paced
control is based on the calculated dose, which is derived from the following online monitoring data
(Leong etal. 2008):
• Flow rate
• UVT
• Lamp power (including lamp age and on-line intensity output data)
Dose-paced control more closely matches the UV dose delivered to wastewater conditions. For example,
during periods of high solids removal, UVT will increase and UV output can be decreased to achieve the
same dose. During wet weather events or other periods of low effluent quality, lamp output can be
increased in response to reduced UVT.
At the University of California, Davis Wastewater Treatment Plant, process controls were
implemented to divert flow automatically to one of two channels during low flow conditions (Phillips
and Fan 2005). This change provided the flexibility to operate at 33, 50, 67 and 100 percent of maximum
power. The original design limited operation to 67 and 100 percent of maximum power. The annual
Evaluation of Energy Conservation Measures 6-5 September 2010
-------
energy use at the DC Davis WWTP is expected to decrease by 25 percent once the process changes are
fully implemented in the fall of 20102.
Lamp Cleaning and Replacement
The effectiveness of UV disinfection systems depends on the intensity of the ultraviolet
radiation to destroy the microorganisms in the treated wastewater. Two factors that affect UV intensity
during operation are lamp age and quartz sleeve fouling.
After an initial burn-in period, the lamp output decreases gradually toward the end of lamp life.
The "end of lamp life" is defined by the manufacturer and is operating hours at which the lamp reaches
a specified minimum output. The operating life of UV lamps is provided below (WEF and ASCE 2010):
• Low-pressure, low-intensity lamps: 7,500 to 8,000 hours
• Low-pressure, high-intensity lamps: 12,000 hours
• Medium-pressure lamps: 5,000 hours
WWTPs can provide a relatively consistent level of lamp output by establishing a schedule for staging
lamp replacements.
Algal growth, mineral deposits, and other materials can foul the lamp sleeve and subsequently
decrease UV intensity and disinfection efficiency. Cleaning and maintaining quartz sleeves are critical to
ensuring the optimum performance of UV disinfection and can result in substantial energy savings. Most
equipment suppliers provide automatic cleaning mechanisms which consist of chemical cleaning,
mechanical cleaning, or both. One study found that a combination of mechanical and chemical cleaning
was superior to mechanical cleaning alone (Peng et al. 2005, cited in Leong et al. 2008).
The Efficiency Partnership (2001) presents an example of energy savings due to increased
attention to UV system cleaning and lamp replacement. At the Central Contra Costa Sanitary District
(CCCSD), lamp cleaning and maintenance is particularly important because they are disinfecting
secondary effluent with fairly low water quality. CCCSD found that increased maintenance of the UV
lamps (i.e. the cleaning and replacement of UV bulbs) at its wastewater treatment facility resulted in a
reduction in the number of UV banks required for the disinfection system from nine to six banks.
Efficiency Partnership (2001) reported that this new maintenance strategy resulted in a power savings of
105 kW. Additional information is available online at
http://www.fypower.org/pdf/CS Water CCCSD.pdf.
6.3 Membrane Bioreactors (MBRs)
Membrane bioreactors (MBRs) are becoming more common as WWTPs are required to meet
increasingly stringent effluent limits and in some cases, reuse requirements in smaller footprints. The
unique feature of MBRs is that instead of secondary clarification, they use membrane treatment, either
as vacuum-driven systems immersed in a biological reactor or pressure-driven membrane systems
located external to the bioreactor, for solids separation. Membranes are typically configured hollow
tube fibers or flat panels and have pore sizes ranging from 0.1 to 0.4 microns. Although MBRs have
2 Readers may contact David Philips (530-754-8214, dxphillips@ucdavis.edu) or Michael Fan (530-752-7553,
mmfan@ucdavis.edu) for additional information.
Evaluation of Energy Conservation Measures 6-6 September 2010
-------
many operational advantages, they use more energy than conventional processes in order to move
water through the membrane and for membrane scouring and cleaning. WEF (2009) reports that energy
requirements of MBR systems may be twice that of conventional activated sludge systems.
Because the technology is not widespread, ECMs for MBRs are emerging. The emerging ECM
identified in this report is membrane air scour alternatives.
Membrane fouling has been identified as the most significant technical challenge facing this
technology (Ginzburg et al. 2008). Fouling occurs when the membrane pores become obstructed with
the mixed liquor suspended solids being filtered, causing a loss in permeability. The main causes of
membrane fouling are initial pore blocking where particles smaller than the membrane pore size plug
the openings, followed by cake fouling, where particles accumulate on the membrane over time forming
stratified "cake" layers (Peeters et al. 2008; Lim and Bai 2003). Although different membrane
manufacturers use different techniques to control for fouling, the primary method to address cake
fouling is aeration along with periodic chemical cleaning. Peeters et al. (2007) report that membrane
aeration to control fouling accounts for 35 to 40 percent of total power consumption of an MBR.
In recent years, several membrane manufacturers have modified operational strategies to
reduce air scour fouling control requirements (Wallis-Lage and Levesque 2009). For example,
Kubotavaries the volume of air used for aeration based on the flux (e.g., lower air scour rates are used
for lower flux values). The manufacturer of the Huber system claims reduced energy consumption for
air scour due to a centrally positioned air intake and low pressure.3 . Siemens uses a combination of air
and water to scour the membrane (Wallis-Lage and Levesque 2009). General Electric (GE) implemented
"cyclic" air scour whereby aeration would turned on and off in 10 second intervals. A newer innovation
is their 10/30 Eco-aeration where the membrane is scoured for 10 seconds on, 30 second off during
non-peak flow conditions. GE claims that the 10/30 Eco-aeration can reduce energy consumption by up
to 50 percent compared to the standard 10/10 aeration protocol (Ginzburg et al. 2008).
The literature includes pilot- and full-scale test data for a membrane fouling controller and
algorithm used to clean the GE ZENON ZeeWeed MBR. They system uses real-time analysis of the
membrane's filtration operating conditions to determine the fouling mechanism present in the MBR
system. The information obtained from the algorithm dictates the implementation of specific control
actions to respond to the particular fouling mechanism (e.g., membrane aeration, backwash, chemical
cleaning - the biggest impact on energy consumption being membrane aeration). When aeration is
identified as the control action, the fouling controller/algorithm provides the MBR Programmable Logic
Controller (PLC) system the information to select between the traditional 10/10 (air scour On/Off)
protocol and a 10/30 Eco Aeration energy saving protocol. The algorithm was piloted and later full-scale
tested at a 3 million gallon per day (mgd) plant in Pooler, Georgia (Ginsburg et al. 2008). Ginzburg (2008)
concluded that additional research is required to further develop the on-line fouling controller to
include additional control parameters such as membrane aeration flow rate, backwash flow rate, and
backwash duration.
3 For more information, visit the manufacturer's website at http://www.huber.de/products/membrane-bioreactor-
mbr/huber-vrmr-bioreactor.html
Evaluation of Energy Conservation Measures 6-7 September 2010
-------
6.4 Anoxicand Anaerobic Zone Mixing
Many WWTPs are implementing biological nutrient removal (BNR) for nitrogen and /or
phosphorus to protect receiving waters and prevent eutrophication, particularly in coastal regions.
Biological nitrogen removal is a two step process consisting of nitrification to convert ammonia to
nitrate (NO3) followed by denitrification to convert nitrate to nitrogen gas. Nitification of ammonia is an
aerobic process and can occur in the aerated zone with sufficient solids residence time (SRT). Significant
energy can be required for complete nitrification of ammonia. Denitrification is an anoxic process
accomplished in the absence of dissolved oxygen so that the microorganisms will use nitrate as their
oxygen source. Dentrification can be accomplished in a denitrifying filter, but most often, it occurs in a
suspended growth anoxic zone where the denitrifying microorganisms can use organic material present
in the wastewater instead of or in addition to an external carbon source. A common configuration of the
suspended growth nitrification-denitrification process is the Modified Ludzack-Ettinger (MLE) process,
which has an initial anoxic zone followed by an aerobic zone. Nitrification occurs in the aerobic zone
from which pumps recycle nitrate-rich mixed liquor to the anoxic zone for denitrification.
Biological phosphorus removal works by exposing the biomass first to anaerobic conditions. As
long as a sufficient food source (i.e., volatile fatty acids) is present, microorganisms called phosphate
accumulating organisms (PAOs) will release stored phosphorus in the anaerobic zone, which conditions
them to uptake larger amounts of phosphorus when they enter the aerobic zone. Phosphorus is
removed when biomass is wasted from the aerobic zone.
It is important to mix the wastewater in the anoxic zone to maintain suspension of solids and
ensure that denitrifying microorganisms come into contact with nitrate. Similarly, it is important to mix
the wastewater in the anaerobic zone to maintain suspension of the solids and PAIs. The mixers,
however, cannot impart oxygen to the water (this would cause them to use oxygen as their electron
exceptor instead of nitrate). Similarly for the anaerobic zone in biological phosphorus removal systems,
mixers are needed to contact waste and microorganisms but must not transfer oxygen to the water
(oxygen would promote growth of microorganisms other than PAOs which would compete with them
for the food source). Low-speed submersible mixers are commonly used for these processes.
Two emerging ECMs have been identified to reduce the energy required to mix anoxic and
anaerobic zones: hyperbolic mixers and pulsed large bubble mixing.
6.4.1 Hyperbolic Mixer
A new hyperboloid mixer has undergone full-scale testing at two large wastewater treatment
plants in the U.S. and has shown significant energy savings compared to traditional submersible mixers.
The mixer is a vertical shaft-type mixer with a hyperboloid-shaped stirrer located close to the bottom of
a tank. The stirrer is equipped with transport ribs that cause acceleration of the wastewater in a radial
direction to promote complete mixing (see Figure 6-2 for a schematic). The hyperboloid mixer has been
used in Europe for more than ten years with installations in Germany, Holland, and Belgium (Gidugu et
al. 2010).
Evaluation of Energy Conservation Measures 6-8 September 2010
-------
GEAR REDUCER
PITCH BLA.DE
PITCH BLADE
HYPEREOLDID IMPELLER
Hyperboloid Mixer
Figure 6-2. Typical Installation of a Hyperboloid Mixer
Source: Gidugu et al. 2010. Used with permission.
Evaluation of Energy Conservation Measures
6-9
September 2010
-------
A recent study at the Bowery Bay Water Pollution Control Plant (WPCP) in New York City
compared the performance of traditional submersible mixers (specifically 2 blade propeller mixers
mounted to the side of the tank) to a hyperbolic mixer, the HYPERCLASSIC HC RKO 2500® (Fillos and
Ramalingam 2005) for anoxic zone mixing. Researchers evaluated the two mixers based on their ability
to:
• Sustain uniform distribution of suspended solids in the basin,
• Maintain a low DO concentration (< 0.3 milligrams per liter), and
• Maintain a hydraulic profile supportive of denitrification (as determined using tracer tests).
Although both mixers at the Bowery Bay WPCP were able to achieve good distribution of solids with low
DO, the Hyperclassic mixer had a superior hydraulic profile. Moreover, the authors reported lower
energy needs for the Hyperclassic mixer due to its design: 2.2 brake horsepower (bhp) for the
Hyperclassic mixer compared to 6.0 bhp for the submersible mixer. The authors reported a total energy
cost of $1,131 for the Hyperclassic mixer compared to $3,075 for the submersible mixer per anoxic zone
per year, for a savings of close to $2,000 based on a current energy rate of $0.039 per kWh4. The capital
cost of the Hyperclassic mixer is approximately $10,000 more than the uniprop mixer, so simple payback
would be approximately five years per anoxic zone.
Gidugu et al. (2010) reported results of side by side testing of the new hyperboloid mixer and a
conventional hydrofoil mixer at the Blue Plains WWTP in Washington, D.C. The hydrofoil mixer, which is
widely used in the U.S., has a vertical shaft and a hydrofoil impeller with four angled stainless steel
blades (Gidugu et al. 2010). See Figure 6-3 for a schematic of the hydrofoil mixer. Two 20 hp hydrofoil
mixers were installed in one of the anoxic zones at the Blue Plains WWTP in October 2004 for
evaluation. Six 10 hp hyperboloid mixers were installed in three anoxic zones (two per zone) for testing
in October 2008. Researchers collected data to create DO and TSS profiles in all four anoxic zones in
June 2008 to evaluate mixing.
Results showed similar results to Bowery Bay WPCP, with the hyperboloid mixer achieving good
distribution of solids with low DO. TSS concentrations within the hyperboloid mixer were spread out
over a smaller range of values than within the traditional hydrofoil mixer, indicating more uniform
mixing. Gidugu et al. (2010) present a comparison of energy use, citing 9.7 bhp per unit for the 10 hp
hyperboloid mixer compared to 17.3 bhp for the hydrofoil mixer. Based on an electricity cost of
$0.10/kWhr, they estimated energy savings potential of over $5,000 per year per mixer. At a cost
difference of only $2,000 more for the hyperboloid mixer compared to the hydrofoil mixer, simple
payback would be less than one year.
Based on this information, energy use for the Hyperclassic mixer would be 29,000 kWh/yr compared to 78,850
kWh/yrforthe submersible mixer for an energy savings of 49,850 kWh/yr per anoxic zone.
Evaluation of Energy Conservation Measures 6-10 September 2010
-------
GEAR REDUCER
SHAFT
HYDROFOIl IMPEUER
WITH 4BIADES
fO'-1Q"
Conventional Hydrofoil Mixer
Figure 6-3. Conventional Hydrofoil Mixer
Source: Giduguetal. Used with permission.
Evaluation of Energy Conservation Measures
6-11
September 2010
-------
6.4.2 Pulsed Large Bubble Mixing
An innovative mixing technology by Enviromix called BioMx reduces energy required for anoxic or
anaerobic zone mixing by firing short bursts of compressed air into the zone instead of mechanically
mixing it. Uniquely designed nozzles produce a mass of large air bubbles, ranging from marble to softball
size, which mix the water as they rise to the surface (Randall and Randall 2010). The large air bubbles,
much larger than those made by coarse bubble diffusers, are designed to minimize oxygen transfer and
maintain anoxic or anaerobic conditions. The system includes a PLC to manage the timing of the air
control valve firing, which gives the operator flexibility to respond to different conditions within the
tank. The manufacturer reports that the system has non-clogging, self cleaning in-tank components that
require no maintenance. See Figure 6-4 for a typical installation and the manufacturer's website for
additional information (http://www.enviro-mix.com/biomx.php).
Figure 6-4. Typical BioMix Installation
Source: EnviroMix. Used with permission
An independent study at the F. Wayne Hill Water Resources Center in Gwinnett County, Georgia
compared the performance and energy use of BioMx to submersible propeller mixers (Randall and
Randall 2010). The plant, treating 30 mgd on average with a design flow of 60 mgd, operates up to 10
parallel treatment trains each with anaerobic, anoxic, and aerobic zones for biological nitrogen and
phosphorus removal. In the spring of 2009, the BioMx system was installed in two anaerobic cells of one
treatment train. The system consisted of an Ingersoll Rand 5 - 15 hp variable speed rotary screw
compressor, piping, controls, and floor mounted nozzles. Findings from the technology evaluation
performed in January 2010 are summarized below.
• Dye tracer tests showed similar mixing for the BioMx and submersible mixer systems.
• Total suspended solids (TSS) profiles showed that the BioMx unit is capable of mixing to
homogeneity similarly to the submersible mixing units, although variability in the BioMxcells
was slightly higher.
Evaluation of Energy Conservation Measures
6-12
September 2010
-------
• Continuous oxidation reduction potential (ORP) measurements over periods of 12 to 28
hours showed 95th percentile ORP values of less than -150 millivolts (mv), which is indicative
of anaerobic environments. Given the success in anaerobic environments (< -100 mv), the
technology is also applicable for use in anoxic environments.
• Power analyzer readings taken simultaneously showed that energy (in kW) required to mix
one anaerobic cell using the BioMx system was 45 percent less than the energy required by a
submersible mixer. When operated in three cells using the same compressor, 60 percent
less energy was required (0.097 hp/1000 cf)
The manufacturer also presents test results conducted from April 2009 through February 2010, available
online at http://www.enviro-mix.com/documents/FWavneHillEnergvSuccessStory2009-091001.pdf.
6.5 References
Cooper, N., J. Marshall, K. Hunt, and J. Reidy. 2007. Less Power, Great Performance System
modifications shrink a Georgia membrane bioreactor's power demand. Water Environment &
Technology. Alexandria, VA: WEF. 19(2): 63-66.
Efficiency Partnership. 2001. Water/Wastewater Case Study: Central Contra Costa Sanitary District. Flex
Your Power. http://www.fypower.org/pdf/CS Water CCCSD.pdf. Retrieved January 27, 2010.
Faber, J. 2010. Email communication to the author. March 26, 2010.
Fillos, J. and K. Ramalingam. 2005. Evaluation of Anoxic Zone Mixers at the Bowery Bay WPCP. New York
City Department of Environmental Protection, Process Planning Section, Division of Operations Support,
Bureau of Wastewater Treatment. Contract # PW-047.
Gidugu, S., S. Oton, and K. Ramalingam. 2010. Thorough Mixing Versus Energy Consumption. New
England Water Environment Association Journal, Spring 2010.
Ginzburg, B., J. Peeters, and J. Pawloski. 2008. On-line Fouling Control for Energy Reduction in
Membrane Bioreactors. Presented at Membrane Technology 2008. Atlanta, GA. WEF.
Leong, L.Y.C., J. Kuo, and CTang. 2008. Disinfection of Wastewater Effluent— Comparison of Alternative
Technologies. Water Environment Research Foundation (WERF), Alexandria, VA.
Lim, A.L and R. Bai. 2003. Membrane Fouling and Cleaning in Microfiltration of Activated Sludge
Wastewater. Journal of Membrane Science. 216 (2003), 279-290.
Pacific Gas and Electric Company (PG&E). 2001. Energy Benchmarking Secondary Wastewater Treatment
and Ultraviolet Disinfection Processes at Various Municipal Wastewater Treatment Facilities. San
Francisco, CA. Available online at http://www.ceel.org/ind/mot-sys/ww/pge2.pdf .
Peeters, J., J. Pawloski and J. Noble. 2007. The evolution of immersed hollow fibre membrane aeration
for MBR, IWA4th International Membrane Technologies Conference, Harrogate, UK.
Peng, J., Y. Qiu, and R. Gehr. 2005. Characterization of Permanent Fouling on the Surfaces of UV
LampsUsed for Wastewater Disinfection. Water Environ. Res. 77(4), 309-322.
Evaluation of Energy Conservation Measures 6-13 September 2010
-------
Phillips, D. L. and M. M. Fan. 2005 Automated Channel Routing to Reduce Energy Use in Wastewater UV
Disinfeciton Systems. University of California, Davis. Davis, California.
Randall, C.W. and W. O. Randall. 2010. Comparative Analysis of a Biomix System and a Submersible
Propeller Mixer: Mixing in Anaerobic Zones at the F. Wayne Hill Water Resources Center, Buford,
Georgia. Report provided in an e-mail from Clifford W. Randall to the author on May 4, 2010.
Salveson, A., T. Wade, K. Bircher, and B. Sotirakos. 2009. High Energy Efficiency and Small Footprint
with High-Wattage Low Pressure UV Disinfection for Water Reuse. Presented at the International
Ultraviolet Association (IUVA)/ International Ozone Association(IOA) North American Conference. May
5, 2009. Boston, MA
USEPA. 1999. Wastewater Technology Fact Sheet: Ultraviolet Disinfection. Office of Water. EPA 832-F-
99-064. Available online at http://www.epa.gov/OWM/mtb/uv.pdf
USEPA. 2006. Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface
Water Treatment Rule. Office of Water. EPA 815-R-06-007. Available online at
http://www.epa.gov/safewater/disinfection/lt2/pdfs/guide It2 uvguidance.pdf
Wallis-Lage, C.L. and S. D. Levesque. 2009. Cost Effective & Energy Efficient MBR Systems. Presented at
the Singapore International Water Week. June 22 - 26, 2009. Suntec Singapore International
Convention and Exhibition Center. Available online at
http://bvwater.files.wordpress.com/2009/05/abstract siw09 wallis-lage.pdf
WEF and ASCE. 2010. Design of Municipal Wastewater Treatment Plants - WEF Manual of Practice 8 and
ASCE Manuals and Reports on Engineering Practice No. 76, 5th Ed. Water Environment Federation,
Alexandria, VA, and American Society of Civil Engineers Environment & Water Resources Institute,
Reston, Va.
WEF. 2009. MOP No. 32: Energy Conservation in Water and Wastewater Facilities. Prepared by the
Energy Conservation in Water and Wastewater Treatment Facilities Task Force of the Water
Environment Federation. McGraw Hill, New York.
Evaluation of Energy Conservation Measures 6-14 September 2010
-------
7. Energy Conservation Measures for Solids Processing
Chapter 7 covers:
7.1
7.2
7.3
7.4
7.5
Introduction
Digestion
Incineration
Thermal Drying
References
7.1 Introduction
Wastewater utilities use a variety of treatment techniques to convey, store, and process solids.
Biological, chemical, or thermal stabilization processes are used to reduce pathogens, vector attraction,
and odors. These are commonly followed by dewatering techniques to concentrate the solids before
disposal. Concentrating the solids removes excess liquid that can be recycled to the head of the
treatment plant and reduces the hauling and disposal expense. The final treated product is either sent
to a landfill (which is becoming less common), incinerated, or reused as land-applied biosolids or
biosolids products. The energy used to process residual solids at a wastewater treatment plant (WWTP)
varies greatly depending on the treatment and dewatering techniques used.
Sections 7.2 and 7.3 identify innovative energy conservation measures (ECMs) for digestion and
incineration, respectively, and provide supporting data from case histories. Section 7.4 describes an
emerging ECM for thermal drying: solar drying. Although several sources cite a growing use of solar
drying beds, full scale operating data have not been identified (thus, it's categorization as emerging).
The reader is referred to the Water Environment Federation (WEF) Manual of Practice (MOP) No. 32,
Energy Conservation in Wastewater Treatment Facilities (2009) for general guidance on designing and
operating solids treatment processes to reduce energy use.
7.2 Digestion
Aerobic and anaerobic digestion are common methods used to stabilize sludge at wastewater
treatment plants. Aerobic digestion is an energy intensive process that breaks down organic material in
the presence of oxygen. It generally produces less residual solids than anaerobic digestion and is easy to
operate; however, in addition to being energy intensive, it produces a sludge that is difficult to dewater
and may further decompose, potentially causing odor problems (WEF 2009). Anaerobic digestion is a
fairly energy efficient process that breaks down volatile organic matter into methane, carbon dioxide,
ammonia, and water in the absence of oxygen. The biogas produced by anaerobic digestion can be
captured and used to generate electricity and heat.
WEF (2009) describes the following ECMs that can be used to conserve energy during aerobic
digestion:
• Aerobic-anoxic operation
• Operation at low dissolved oxygen (DO) concentrations
Evaluation of Energy Conservation Measures 7-1 September 2010
-------
• Reducing digestion time by meeting vector attraction criteria using the specific oxygen
uptake rate (SOUR)
• Assessing optimal solids concentration
Because methods for introducing oxygen to aerobic digesters are similar to methods used for aeration,
ECMs for aeration as described in Chapters 4 and 5 of this report can also be considered for aerobic
digestion. For example, replacing coarse bubble with fine bubble diffuser systems and use of automated
DO control can reduce aerobic digestion energy requirements by 20 to 50 percent.1 ECMs are most
effective if the digester is oxygen limited rather than mixing limited (i.e., the air flow rate needed to
supply oxygen exceeds the air flow rate needed to maintain proper solids suspension). Engineers should
use caution because some plants have observed premature wear of fine bubble diffusers due to the
abrasive nature of the thickened solids. Wear of the diffusers can be minimized by incorporating proper
grit removal in the influent treatment process.
Many techniques can be used to optimize biogas production by anaerobic digesters. For
example, increasing the primary solids concentration and adequate mixing can aid in digester gas
production. Adding fat, oil, and grease from restaurant and factory grease traps will yield, perhaps, the
largest increase in gas production. EPA is evaluating various technologies for combined heat and power
used at wastewater facilities and will publish the results as a separate report. The remainder of this
section describes a relatively new ECM for anaerobic digestion: use of the vertical linear motion mixer.
Vertical Linear Motion Mixer
Effective mixing of the digester contents is important for process stability, to prevent solids
deposition, and to minimize scum and foam formation. Mixing is commonly achieved with recirculation
pumps, gas mixers that bubble digester gas up through the tank, or conventional propeller-type mixers
that stir the digester contents. A new technology called the vertical linear motion mixer from Enersave
Fluid Mixers, Inc., mixes digester contents by moving a thin steel disk in an up and down motion to
create axial and lateral agitation. An internal Cam-Scotch-Yoke drive electric motor operating system
converts the rotary motion of a motor to the vertical (up and down) motion of the drive shaft. See
Figure 7-1 for a schematic of the mixer. The manufacturer claims as much as 90 percent energy
reduction from the vertical linear motion mixer compared to conventional mixing technologies.
Additional information on the technology can be found on the manufacturer's website at
http://www.enersavemixers.com/.
1 E-mail communication with Thomas E. Jenkins, August 4, 2010.
Evaluation of Energy Conservation Measures 7-2 September 2010
-------
Figure 7-1 Vertical Linear Motion Mixer by Enersave Fluid Mixers, Inc.
Source: http://www.enersavemixers.com/. Used with permission
Massart et al. (2008) presents results of side-by-side testing of the vertical linear motion mixer
and conventional mixing at the Ina Road Wastewater Reclamation Facility (WRF) in Tuscon, Arizona. The
Ina Road WRF, treating approximately 25 million gallons per day (mgd), operates four anaerobic
digesters to stabilize combined waste solids from primary clarifiers, a high-purity oxygen activated
sludge system, and waste activated sludge from a biological nutrient removal process. Each digester is
approximately 90 feet in diameter and 40 feet deep. The digesters were originally each equipped with
four peripheral 20 hp (15 kW) rotary draft tube impellers and one 10 hp rotary draft tube impeller in the
Evaluation of Energy Conservation Measures
7-3
September 2010
-------
center of the basin. A new vertical linear motion mixer was installed in Digester 4 in December 2003.
The single 10 hp mixer consisted of a 7-foot diameter disk located approximately 18 feet below the
digester surface. Based on manufacturer's experience at similar installations, only one central mixing
unit was installed to fully mix the basin contents. The motor operates the disk up and down at
approximately 0.5 cycles per second.
A tracer test was conducted to analyze the performance of the new system and compare its
operation to that of a mechanically mixed basin (Digester 2). Results, presented in Massart et al. (2008),
show that both the mechanically mixed basin and the basin with the linear motion mixer achieved a
similar degree of mixing with neither showing an advantage over the other. Solids and temperature
measurements showed homogeneity of the basin contents, confirming good mixing. The authors'
review of historical data from January 2004 through April 2007 revealed good performance of the
vertical linear motion mixer, although they noted that the digesters were not highly loaded or operated
at a high solids concentration during the analysis period.
Massart et al. (2008) identified a unit power rating of 1.315 kW per 1,000 cubic meters
(kW/1000m3) for the vertical linear motion mixer compared to a unit power rating of 12.113
kW/lOOOm3 for the existing draft tube mixers2. This example is consistent with the manufacturer's
claims that the linear motion mixer operates at a fraction (approximately 10 percent) of the energy
needed for a conventional mixer. In addition to energy savings, the authors predicted reduced
maintenance requirements since there is only one disk compared to five mechanical impeller units for
the conventional system.
7.3 Incineration
Incineration is the process of sludge combustion to produce an inert ash with a significantly
reduced volume (90 percent or more reduction) compared to the influent solids loading. The two most
common sewage sludge incineration technologies are the multiple hearth furnace (MHF) and the
fluidized-bed furnace (FBF). The multiple hearth furnace was the most common type of incinerator used
at WWTPs; however WEF (2009) reports that nearly all installations in the past 20 years have been FBFs.
The energy required for incineration depends on many factors, including the moisture and
organic content of the sewage sludge, air pollution requirements, and operating practices. In recent
years, advances in flue gas recirculation and exhaust heat recovery/reuse have made incineration more
economical and less energy intensive (WEF 2009). Many of the incinerators being installed today are
equipped with flue gas recirculation and waste heat recovery systems integral to the design of the
furnace. Flue gas recirculation allows the furnace to be operated at a lower temperature while
controlling air emissions, minimizing fuel consumption and reducing maintenance (through reduced ash
slagging). Recovered heat energy from the furnace exhaust can be utilized to pre-heat the combustion
air fed to the furnace. Since combustion air represents a significant heat load (fuel consumption
requirement) to the furnace, pre-heating combustion air with waste heat reduces the amount of fuel
required by the furnace to effect sewage sludge incineration.
2 Revised numbers provided in email communications from Neil Massart, Process Engineer, Black & Veatch.
August 5, 2010.
Evaluation of Energy Conservation Measures 7-4 September 2010
-------
Older MHFs without these energy saving features can be modified and upgraded to incorporate
waste heat recovery/combustion air pre-heating, not only resulting in fuel savings but also increasing
furnace capacity and reducing maintenance. The following describes how the Washington Suburban
Sanitary Commission (WSSC) was able to save approximately 320,000 therms (equivalent to 32,000,000
cubic feet) of natural gas per year (a 76% reduction), saving approximately $400,000 per year in energy
costs while at the same time increasing incinerator capacity.
The WSSC Western Branch WWTP is a 30 mgd plant that includes a denitrification activated
sludge (DMAS) biological nitrogen removal process utilizing methanol addition for biological
denitrification and chemical precipitation for enhanced biological phosphorus removal. Biosolids are
thickened and dewatered using dissolved air flotation and centrifuges, respectively, and are
subsequently incinerated in two natural gas fired MHFs. The furnaces were commissioned in 1974 and
in 1977 (as part of the Phase I and Phase II plant modifications, respectively) and were originally
designed to process 26 dry tons per day (dtpd) of heat treated biosolids. WSSC decommissioned the
biosolids heat treating process at the Western Branch WWTP soon after commissioning the second MHF
in 1977. In 2001, to comply with the promulgation of Title V and "zero visible emissions" requirements
of the Clean Air Act, the capacity of the MHFs was reduced to 12 dtpd and external afterburners were
installed, which increased natural gas consumption.
The MHFs were retrofitted in 2009 and 2010 with Flue Gas Recirculation (FGR) systems that take
the exhaust flow from the top hearth of the furnace and re-injects it into the one of the lower hearths.
The recirculated flue gas mixes with the higher temperature combustion gases, providing ample time
and heat to completely oxidize volatile hydrocarbons released from the sludge feed entering the top
hearth of the MHF. This allows the furnace to be run at a lower temperature (or without an exhaust gas
afterburner), optimizing fuel consumption and eliminating ash slagging (i.e., melting of ash inside the
furnace when operated at high temperature to reduce smoky and odorous emissions). The MHFs were
also retrofitted with air-to-air waste heat recovery heat exchangers that recover and utilize the heat
contained in the furnace exhaust streams (exhaust combustion air and center shaft cooling air) to
preheat the furnace combustion air, reducing both the heat load to and fuel consumption of the
furnace. Circle Slot Jets were added to the furnaces to convey the preheated combustion air into the
hearths to increase turbulence and air-fuel mixing. The improved convection and turbulence increased
drying and combustion rates of the furnaces and subsequently increased their capacity from 12 to 17
dtpd (a 42% to 58% capacity increase). Figure 7-2 is a schematic representation of the ECM
modifications to the Western Branch WWTP MHFs.
Evaluation of Energy Conservation Measures 7-5 September 2010
-------
TO
EXHAUST
CLEAN
EXHAUST
IRCLESLOT
JETS
Air Injection
Figure 7-2 Schematic Representation of Multiple Hearth Incinerator Energy Efficiency Improvements at WSSC Western Branch
WWTP
Source: Provided courtesy of WSSC. Circle Slot Jet copyright held by American Heat and Power.
The total cost of the retrofits was $4.5 million. With annual natural gas cost savings of
approximately $400,000, the simple payback of the project was approximately 11 years. For more
information, see the case study summary in Chapter 8 and the full case study description including
schematics and detailed operating information in Appendix A.
7.4 Thermal Drying
Thermal drying is the use of heat to evaporate residual water from sludge. It typically follows
dewatering and can increase the dry solids content from between 18 and 30 percent to more than 90
percent (WEF 2009). The thermal drying process reduces the mass and volume of dewatered solids and
results in a product with a high nutrient and organic content that can be used as a low-grade fertilizer. A
Evaluation of Energy Conservation Measures
7-6
September 2010
-------
major advantage of heat drying compared to other techniques is that it is ideal for producing Class A
biosolids.3(USEPA2006)
Methods for thermal drying are direct or indirect depending on the way that thermal energy is
transferred to the sludge. Direct, also called "convection," dryers move hot air through a vessel where it
comes into contact with the wet solids. Types of convection dryers include rotary drum, flash, and
fluidized bed (WEF and ASCE 2010). Indirect, also called "conduction," dryers separate wet solids from
the heat transfer medium typically with a solid metal wall. Types of dryers include the paddle, hollow-
flight, and rotary chamber dryer. Simpler materials handling and emissions control have made
conduction dryers more popular with medium and small systems.
The energy required for thermal drying includes fuel/thermal energy and electricity to operate
equipment. USEPA (2006) cites a typical efficiency rate of 1,400 to 1,700 Btu per pound of water
evaporated. Conventional thermal dryers use a large amount of fuel compared to other processes (e.g.,
composting and land application); however, they generally produce a higher quality product on a more
consistent basis. External fuel requirements for thermal drying can be reduced by using an onsite
energy source such as anaerobic digester gas or wood chips. Recycling of heated gas can also reduce
fuel requirements (USEPA 2006).
WEF and ASCE (2010) report on growing use in Europe and the United States of an emerging
ECM for thermal drying called solar drying. First developed by researchers in Germany, solar drying uses
solar energy and convective air drying methods to produce solids containing no more than 10 percent
moisture. Solar dryers consist of a wide concrete pad with low walls enclosed in a "greenhouse" type
structure. Sludge is pumped onto the pad and arranged in a relatively thin layer or in windrows. A
microprocessor monitors temperature and humidity and adjusts fans and louvers to provide sufficient
ventilation for drying. Auxiliary heat may be used to enhance drying performance.
Figure 7-3 shows an example of a solar dryer manufactured by the Parkson Corporation. As of
2008, WEF and ASCE (2010) report that 10 solar drying facilities are being built or operated in the U.S.,
mainly at small plants.
The Parkson Corporation reports that approximately 95 percent of energy used for drying is
provided by solar panels. They cite 100 installations in a variety of climates and for WWTP sizes ranging
from 0.2 to 40 mgd. Solar drying is considered an emerging ECM because of its capacity to significantly
reduce fuel requirements compared to conventional dryers. Disadvantages of the technology are its
large footprint, the need for sufficient days with adequate solar heating, and potential for odor
problems. If odors are present, appropriate control technologies is available and can be provided.
Class A biosolids are defined in 40 CFR Part 503 as biosolids that have met "the highest quality" pathogen reduction
requirements confirmed by analytical testing and/or the use of a Process to Further Reduce Pathogens (PFRP) as defined in 40
CFR Part 257.
Evaluation of Energy Conservation Measures 7-7 September 2010
-------
A large louver controls
the fresh air inlet into
the drying chamber
Several sensors monitor the
climatic conditions inside
and outside of the
drying chamber
A PLC carries a complex drying program
that controls and monitors the entire
drying process. The operation of all
devices is completely automated
Speed controlled "ceiling
fans" provide optimal air flow and
distribution over the sludge
The drying
chamber is
enclosed by
a highly
transparent
and well
insulated cover
to prevent
uncontrolled
air exchange
and heat loss
Liquid or ——-
dewatered
sludges
The Electric Mole™ mixes, aerates and
granulates the sludge in regular
intervals. The Electric Mole™ is made of
stainless steel and is suitable for a wide
variety of sludges
Figure 7-3. Example of Solar Dryer by Parkson . Used with permission.
Several exhaust fans control
the air exchange to maximize
the drying performance
Evaluation of Energy Conservation Measures
7-8
September 2010
-------
7.5 References
Cantwell, J., J. Newton, T. Jenkins, P. Cavagnaro, and C. Kalwara. 2009. Running an Energy-Efficient
Wastewater Utility Modifications That Can Improve Your Bottom Line. WEF Webcast. June 19, 2009.
Massart, N., J. Doyle, J. Jenkins, J. Rowan, C. Wallis-Lage. 2008. Anaerobic Digestion - Improving Energy
Efficiency with Mixing. Presented at WEFTEC 2008, Chicago, IL
Sapienza, F. and T. Bauer. 2005. Thermal Drying of Wastewater Solids. Presented at WEFTEC 2005,
Washington, DC.
USEPA. 2006. Biosolids Technology Fact Sheet: Heat Drying. Office of Water, EPA 832-F-06-029.
September 2006. Available online at http://www.epa.gov/OWM/mtb/heat-drying.pdf.
WEF. 2009. MOP No. 32: Energy Conservation in Water and Wastewater Facilities. Prepared by the
Energy Conservation in Water and Wastewater Treatment Facilities Task Force of the Water
Environment Federation. McGraw Hill, New York.
WEF and ASCE. 2010. Design of Municipal Wastewater Treatment Plants - WEF Manual of Practice 8
and ASCE Manuals and Reports on Engineering Practice No. 76, 5th Ed. Water Environment Federation,
Alexandria, VA, and American Society of Civil Engineers Environment & Water Resources Institute,
Reston, Va.
Evaluation of Energy Conservation Measures 7-9 September 2010
-------
This page left intentionally blank
Evaluation of Energy Conservation Measures 7-10 September 2010
-------
8. Summary of Facility Case Studies
Chapter 8 covers:
8.1 Introduction
8.2 Approach
8.3 Summary of Results
8.1 Introduction
This chapter supplements technical information presented in this report on innovative energy
conservation measures (ECMs) for municipal wastewater treatment plants (WWTPs) with real-world
experience and data analyses of ECM implementation at nine plants. The approach for selecting the
case study facilities is presented in Section 8.2. Section 8.3 summarizes the facility case study results.
Detailed information including process flow diagrams, wastewater quality information, detailed ECM
specifications, and energy consumption and cost data are provided in Appendix A.
8.2 Approach
The following three-step selection process was used to select the nine facilities:
1. An in depth literature review was used to identify more than 30 candidate facilities.
2. The project team conducted screening calls to the candidate facilities to -
• Verify the ECMs;
• Determine the availability of cost and energy savings data;
• Determine utilization of submetering, and;
• Determine if the utility would be willing to participate in the project and provide the
required information.
3. The results of the screening calls were presented to a technical expert panel. The panel was
comprised of experts from the USEPA, private wastewater consulting companies,
wastewater utilities, state environmental programs, and nonprofit organizations. (See the
acknowledgement section of this report for a list of expert panel members.)
The final facilities were selected using the criteria presented in the text box on the following page.
Evaluation of Energy Conservation Measures 8-1 September 2010
-------
Criteria for Selecting Final Nine Case Studies
• The case studies should include innovative blower technologies (air bearing and
mechanical).
• The case studies should include one or more innovative dissolved oxygen (DO) control
systems (e.g., BIOS, DO control using respirometry, solids retention time (SRT) and DO
control using biological process modeling based control algorithms).
• Each should show significant savings and reasonable payback period. Savings should not
be based on poor operations/malfunctioning equipment in place prior to ECM.
• Particularly innovative uses of new equipment should be prioritized.
• To the extent possible, the case studies should be distributed geographically and
represent a range of facility sizes.
• At least one facility should include cost and energy savings data for one or more
conventional ECM (e.g., variable frequency drive (VFD) motor controls, fine bubble
diffusers).
• Where possible, the case study should have at least one year of full-scale operating data.
The case studies were prepared in accordance with written quality assurance protocols (the
Quality Assurance Project Plan). Data and information from the nine selected case study facilities were
collected, analyzed and documented in the case study presentations in accordance with the Plan. The
project team began the data/information collection process by sending a detailed questionnaire to each
wastewater utility's contact person. The questionnaire asked for general information on the facility
(e.g., process description, plant history) and the following information on each ECM installed:
• Description
• Year installed
• Capital and operating costs
• Energy use, costs and savings
• Factors that led to the selection of the ECM and contributed to its success
• Impact(s) on other operations
• Lessons learned
The utilities' responses were reviewed and analyzed based on the project technical team's
experience with similar types of wastewater treatment facilities and energy conservation measures
implemented at similar facilities (i.e., size and process type) and compared across respondents for
consistency. The project team conducted follow-up telephone interviews and used e-mail
communications to ask questions, clarify perceived discrepancies and confirm written information and
data provided by the utilities. All calculations were documented in excel spreadsheets and
independently checked for errors. Draft case studies were sent to the utilities' contacts for review and
Evaluation of Energy Conservation Measures 8-2 September 2010
-------
comment. Final draft case study presentations were subsequently reviewed by USEPA and then peer
reviewed.
8.3 Summary of Results
Table 8-1 summarizes the results of the facility assessments, including a brief description of the
ECMs installed at the facility, capital cost, energy savings, and payback period. A short description of
each case study follows the table. See Appendix A for additional information.
Evaluation of Energy Conservation Measures 8-3 September 2010
-------
Table 8-1. Summary of Facility Case Studies
Case
Study
No.
1
2
3
Facility
Green Bay
Metropolitan
Sewerage District
De Pere, Wl
Sheboygan
Regional WWTP
Sheboygan, Ml
Big Gulch
Wastewater
Treatment Plant,
Mukilteo, WA
Avg Daily
Flow
(MGD)
8.0
11.8
1.5
ECM(s)
Aeration system upgrade:
• Replaced 5 positive displacement blowers with 6
HST® ABS magnetic bearing turbo blowers
Aeration system upgrade:
• Replaced 4 positive displacement blowers with 2
Turblex ® blowers with upgraded DO control and
SCADA
• Installed air control valves on headers, upgraded PCL
• Replaced mechanical aeration with Sanitare fine bubble
diffusers and air bearing KTurbo blowers.
• Upgraded to automated DO control
• Installed automated ORP-based control for nitrification
(dNOx Anoxic Control System)
Project Cost
$850,000
($2004)
$790,000 ($2005)
($773,000 with
$17, 000 utility
incentive) for
blowers,
$128,000 ($2009)
for air control
valves
For Oxidation Ditch
A: $487,066
($2007) -
($447,875 with
$39,191 incentive),
For Oxidation Ditch
B: $1,045,023
($2007) -
($998,429 with
$46,594 incentive),
Energy Savings
$63,758/yr
2,1 43,975 kWh/yr
(50% reduction)
$25,644/yr
associated with
blower replacement
(358,000 kWh/yr-
13% reduction)
$38,245/yr
associated with air
control valves
(459,000 kWh/yr-
17% reduction)
$10,721 per year
(based on Y2010
savings following
Ditch A and Ditch B
commissioning)
$43,756 (for 2010)
based on $0.037
per pound CBOD
removed)
Payback
Period
(Yrs)1
13.3
14
135
33 years
Evaluation of Energy Conservation Measures
8-4
September 2010
-------
Table 8-1. Summary of Facility Case Studies (Continued)
Case
Study
No.
4
5
6
7
Facility
City of Bartlett, TN
Wastewater
Treatment Facility
Oxnard, CA Plant
#32
Bucklin Point -
Narragansett Bay
Commission (Rl)
Washington
Suburban Sanitary
Commission (MD)
Western Brach
WWTP
Avg Daily
Flow
(MGD)
1.0
22.4
23.7
21.6
ECM(s)
Added VFD Control of oxidation ditch rotors using 4-
20mA signal from optical DO probes
Optimization and control of SRT and DO using proprietary
process modeling based control algorithms
DO Optimization Using Floating Pressure Blower Control
and a Most Open Valve Strategy
Solids processing system upgrade:
• Waste Heat Recovery
• Flue Gas Recirculation (FGR)
• Circle Slot Jets (CSJs) Air injection System
Project Cost
$13,500 total
($2007)
$135,000
$200,000 ($2007)
$4,500,000
Energy Savings
$9,176/yr
71,905kWh/yr
(13% reduction)
$26,980/yr
306,600 kWh/yr
(20% reduction)
Average of approx
$1 35, 786/yr for first
3 years
Average of
1, 247,033 kWh/yr
(11. 6% reduction)
for first 3 years
$400,000 /yr
estimated natural
gas
320,000 therms/yr
(76% reduction)
Payback
Period
(Yrs)1
1.5
5
1.5
11.3
Evaluation of Energy Conservation Measures
8-5
September 2010
-------
Table 8-1. Summary of Facility Case Studies (Continued)
Case
Study
No.
8
9
Facility
San Jose/Santa
Clara (CA) Water
Pollution Control
Plant
Waco Metropolitan
Area Regional
Sewer System
(Waco, TX)
Avg Daily
Flow
(MGD)
107
22.8
ECM(s)
Plant pumping systems optimization, BNR pulsed aeration
and DAF Solids Thickening Process optimization using
proprietary process control algorithms
Aeration system upgrade:
• Increased number of diffusers
• Installed DO probes and automatic blower and aeration
system control
Project Cost
$269,569
$397,708
($2002)
Energy Savings
$1,178,811/yrfor
electricity and
natural gas
18.3kW/mg-
average (20%
reduction)
associated with
pumping systems
optimization
1.2 X1011 BTU/yr
(38% reduction)
and 4.8 X 10s
kWh/yr (23%
reduction)
associated with
pulsed air mixing
1, 603,030 kWh/yr
(64% reduction)
associated with
DAF optimization
$331, 272 total
energy savings for
first two years after
ECM installed
4,642,741 kWh/yr
average (33%
reduction)
Payback
Period
(Yrs)1
3 months
2.4
1. Represents simple payback for entire project. In some cases, includes multiple improvements and considers savings from electric utility rebates.
Evaluation of Energy Conservation Measures
8-6
September 2010
-------
Cose Study No. 1, Magnetic Bearing Turbo Blowers at the Green Bay Metropolitan Sewerage District
De Pere Wastewater Treatment Facility
The Green Bay (Wisconsin) Metropolitan Sewerage District's (GBMSD) De Pere Wastewater
Treatment Plant is a 8.0 mgd (average daily flow) two-stage activated sludge plant with biological
phosphorus removal and tertiary effluent filtration. The plant had been running five 450 HP Roots multi-
stage centrifugal blowers for the first stage aeration process. The blowers were approaching the end of
their service life and required either extensive rebuild or replacement. An evaluation conducted by the
plant operations manager and their engineer determined that replacement of the multi-stage
centrifugal blowers with magnetic bearing turbo blowers would reduce the aeration system's energy
consumption and associated cost and reduce the level of maintenance required for the aeration system.
Six ABS, Inc. HST 330 HP magnetic bearing turbo blowers were installed as replacements for the
five 450 HP multi-stage centrifugal blowers in first stage aeration for a capital cost of $850,000. The
turbo blower project reduced the electrical energy consumption by approximately 2,144,000 kWh/yr (a
50% reduction) compared to the costs to operate the multi-stage centrifugal blowers ($170,000 per
year), representing an estimated $63,758 per year (a 38 percent savings) reduction in electrical energy
costs and resulting in a payback estimated at 13.3 years. The blower project also contributed to the
facility's objective of reducing the wastewater treatment plant's electrical energy consumption to
enable a maximum percentage of the required electrical energy being provided by on-site generation
using digester gas fueled microturbines.
Cose Study No. 2, Turblex Blowers and Air Flow Control Valves at the Sheboygan Regional Wastewater
Treatment Plant
The Sheboygan Regional Wastewater Treatment Plant in Sheboygan, Ml is an 11.8 (average daily
flow) mgd activated sludge plant with biological phosphorus removal. The plant had been running four
250 hp Gardner Denver positive displacement blowers for the aeration basins. Typically, two blowers
were required in the summer to provide sufficient aeration, with the remaining two blowers used as
standby units. In 2005, one of the blowers failed and inspection of the remaining three indicated they
would all require complete rebuilds. Instead of rebuilding existing blowers, plant managers decided to
replace the four positive displacement blowers with two 300 hp, high efficiency motor Turblex
centrifugal blowers equipped with inlet guide vanes and variable diffuser vanes. One of the centrifugal
blowers was sufficient to provide the necessary aeration year-round with the second unit operated as
standby unit.
Following commissioning of the Turblex blowers, the plant operators experienced difficulty
controlling dissolved oxygen (DO) in the individual aeration basins. DO levels were reaching as high as 6
mg/L during evening hours and during the winter months, wasting blower output and energy. To correct
this problem, air flow control valves were installed on the headers to each aeration basin. PLC
programming was also upgraded to provide improved control of the DO levels through automatic
operation of the air flow valves and blowers.
The capital cost of the Turblex blowers was $504,000 with a total project cost (capital plus
installation) of $790,000 ($2005). The plant received a $17,000 energy efficiency grant reducing the
project costs to $773,000. The control valves had an installed cost of $128,000 ($2009).
Evaluation of Energy Conservation Measures 8-7 September 2010
-------
The centrifugal blowers saved the plant an estimated 6.2 percent in annual electricity bills,
amounting to an average yearly energy savings of $25,644 for the first three years of operation from
2005 to 2008. The addition of the control valves more than doubled the energy savings, resulting in a
total savings of $63,889 in 2009 and a payback period for both projects of 14 years. The reduction in
energy consumption averaged approximately 358,000 kWh/yrforthe blower replacement project. The
installation of the air control valves resulted in an additional reduction in electrical energy consumption
of 459,000 kWh/yr. Although the plant had delayed installing the air control valves because of cost
issues, they found that poor air control limited their ability to realize the full potential energy savings of
the new blowers.
Cose Study No. 3, Upgrade from Mechanical Aeration to Air-bearing Turbo blowers and Fine Bubble
Diffusers at the Big Gulch Wastewater Treatment Plant
The Big Gulch WWTP, owned and operated by the Mukilteo Water and Wastewater District
(Washington), is a 1.5 mgd (average daily flow) oxidation ditch plant operating two parallel oxidation
ditches. Ditch A treats approximately 40 percent of the plant flow and Ditch B treats approximately 60
percent of the flow. To address increases in biochemical oxygen demand (BOD) and total suspended
solids (TSS) loadings, the oxidation ditch aeration system has been upgraded as follows:
• The existing mechanical brush (rotor) aeration system in the oxidation ditches were replaced
with Sanitaire fine bubble diffusers and 3 turbo blowers (K-Turbo, TB 50-0.6S).
• DO probes with a PLC based control system were installed to automate blower operation.
• A dNOx Anoxic control system was installed to detect the nitrate knee (the point in the nitrogen
conversion process where complete denitrification has occurred, i.e., NO3" has been converted
to N2). With the dNOx control system, the blowers are allowed to go idle as loading increases
and automatically switch on when the nitrate knee is detected.
The aeration systems were replaced sequentially with Ditch A upgraded in 2008 and Ditch B
upgraded in 2009. The total cost of the Ditch A upgrade (including the removal of one aeration rotor and
the installation of one turbo blower, diffusers, probes, and controls) was $487,066. The Big Gulch WWTP
received a $39,191 grant from its electric utility to offset the cost of the project making the total costs
$447,875. The total cost of the Ditch B upgrade (including the removal of four aeration rotors and the
installation of two turbo blower, diffusers, probes, and controls) was $1,045,023. An additional utility
company grant of $46,594 reduced the Ditch B project costs to $998,449.
Observed energy savings following the aeration system upgrade was 148,900 kWH for 2010
(average energy use of 1,405,540 kWH for 2005 through 2008 minus energy use of 1,256,640 kWH in
2010). At a current electricity rate of $0.072/kWH, this translates to an electricity cost savings of
$10,721. Based solely on energy cost savings, this project shows a 135 year payback. While the Big Gulch
project does not meet the case study selection criteria for reasonable payback (as discussed in Chapter
1), it does serve as an example of energy savings derived as a collateral benefit from a major plant
upgrade and expansion. Although a greater reduction in energy consumption would be expected from
this type of aeration system upgrade, it should be noted that the plant experienced a 40 percent
increase in the influent organic loading during the construction and commissioning period, compared to
the period prior to the aeration system upgrade.
Evaluation of Energy Conservation Measures 8-8 September 2010
-------
If an alternative payback analysis is considered that accounts for the 40 percent increase in the
plant's organic loading during the construction and commissioning of the Ditch A and Ditch B upgrades,
the project shows a significantly lower payback of 33 years. In the year following commissioning of the
total project (2010), the plant removed approximately 34 percent more Carbonaceous Biological Oxygen
Demand (CBOD) compared to the period 2004 through 2008 (prior to the implementation of the
oxidation ditch upgrades) while consuming less electrical power (an average of 1.59 kWh/lb CBOD
during the period 2004 through 2008 compared to an estimated 1.06kWh/lb CBOD in 2010). This
translates to a savings in electricity cost of $0.037 per pound of CBOD removed and an estimated
$43,756 for 2010 (a 33 year payback for the total project cost of $1,446,304).
In addition to improved treatment at lower electric consumption, the Big Gulch WWTP
experienced other benefits from the aeration system improvements. The plant experienced a reduction
in labor and maintenance costs as the turbo blowers do not require the level of maintenance required
for the mechanical brush system. Chlorine use (for bulking sludge control) decreased due to improved
settling.
Cose Study No A, Optical DO Sensor technology and Aerator Rotor VFD Control at the City ofBartlett
Wastewater Treatment Plant
The City of Bartlett, TN, WWTP is a 1.0 mgd (average daily flow) secondary facility utilizing two
mechanically aerated oxidation ditches to provide secondary treatment. Each of the aeration basins is
equipped with three rotor aerators. Prior to implementing their aeration system modification ECM
project, each basin was operated using one (each) aeration rotor running continuously and a second
rotor activated daily (and run at full speed) during periods of peak flow.
Under the Demonstration of Energy Efficiency Development Research Program funded by the
Tennessee Valley Authority (TVA) and the American Public Power Association (APPA), the City of Bartlett
Wastewater Division implemented optical DO sensor technology integrated with VFD speed control of
the oxidation ditch rotor aerator. The objective of the TVA/APPA research/demonstration project was to
advance the use of optical DO sensor technology integrated with VFD motor speed control to achieve
energy savings at small to medium sized wastewater treatment facilities (i.e., < 10 MGD) within the TVA
service area.
Under the demonstration program, the DO control setpoint was established in each basin at 1.2
mg/l, and the rotor speed controlled based on the DO readings in the oxidation ditches, relative to
setpoint. During the demonstration program, one rotor in each basin reached full speed for only 20 to
30 minutes each day during the peak flow period. The second rotor was not, and has not ever been,
required to maintain the oxidation ditch DO setpoint concentration.
The optical DO sensor technology and aeration rotor VFD controls were installed and
commissioned for $13,500 ($2007). Following implementation of the aeration system modifications, first
year (2008) energy consumption was reduced by nearly 72,000 kWh (13 % reduction) and peak demand
was reduced by 51 kW (a 39 % reduction). The resulting energy cost savings was $9,176/year (a 22 %
savings). The project resulted in a payback of 1.5 years.
Evaluation of Energy Conservation Measures 8-9 September 2010
-------
Cose Study No. 5, Advanced Aeration Control for the Oxnard, CA Wastewater Treatment Plant
The Oxnard, CA Wastewater Treatment Plant serves a population of approximately 200,000
people and treats an average daily flow of 22.4 mgd. The trickling filter-activated sludge treatment
facility uses Turblex blowers and associated proprietary pressure based control software to automate
the activated sludge aeration process. To address aeration basin foaming and clarifier sludge bulking
problems, the facility implemented activated sludge process optimization and automation utilizing the
following integrated components:
• Replaced the aeration blowers' pressure based control software with DOmaster™ control
software. DOmaster™ (an Ekster and Associates, Inc. proprietary biological process control
software) utilizes biological treatment process modeling based algorithms and process data
mining algorithms to effect DO control.
• Installed InsiteIG optical DO sensor technology replacing outdated membrane probes.
• Installed two total suspended solids (TSS) monitors, one in the mixed liquor channel and one
in the Return Activated Sludge wet well.
• Installed SRTmaster™, Ekster and Associates, Inc. proprietary software providing real time
control of the activated sludge process SRT. The software utilizes a biological process
modeling based control algorithm which maintains minimum variability of wasted solids
(over the course of a day) resulting in significant improvements in solids settling/thickening.
• Installed OPTImaster™, Ekster and Associates, Inc. proprietary software which optimizes the
process control setpoints for SRT and DO in each of the facility's aeration basins.
The effect of these modifications was improved biological process stability and discharge permit
compliance and reduced Sludge Volume Index [SVI] (20% for average SVI and 50% for maximum SVI).
Since the implementation of this ECM, foaming in the aeration basin has not occurred.
In addition to improving the stability of the biological treatment process, improved solids
settling/thickening and elimination of foaming, blower energy consumption was reduced by 306,600
kWh/yr (a 20 % reduction). This reduction in energy consumption represented a nearly $27,000/year
savings in electrical energy costs. Polymer dosage for thickening was reduced as a result of the improved
settleability of the biological solids, resulting in a reduction in chemical costs of $7,500/year.
Additionally, the improved automation of the aeration process reduced labor costs by $18,500/year.
The total project implementation cost was approximately $135,000. The payback, considering
only energy savings was approximately 5 years. Including the chemical cost savings and labor savings in
the payback analysis reduces the payback period to approximately 2.5 years.
Cose Study No. 6, DO Optimization Using Floating Pressure Blower Control in a Most Open Valve
Strategy at the Narragansett Bay Commission Bucklin Point WTF, Rl
The Narragansett Bay Commission's (NBC) Bucklin Point Wastewater Treatment Facility (WWTF)
in East Providence, Rhode Island is a 23.7 mgd (average daily flow) activated sludge
Evaluation of Energy Conservation Measures 8-10 September 2010
-------
nitrification/denitrification facility employing the Modified Ludzak-Ettinger (MLE) process.
Commissioned in 2006, the MLE process aeration system utilized a conventional aeration/blower control
system consisting of individual Proportional-lntegral-Derivative (PID) loops to control DO in and air flow
to each of the MLE process aerobic zones. This control system was based on Most Open Valve (MOV)
logic. The control system modulated blower air flow based on discharge pressure. Each of the air
distribution system's 16 drop legs were modulated independently based on DO measurements in the
aeration basins. The MOV logic was programmed to use the positions of the 16 valves to increase or
decrease the pressure setpoint.
Following commissioning of the MLE process, the plant experienced difficulty attaining
consistent nitrogen removal because the constant pressure based PID aeration control system was
unable to adjust to changing process conditions and maintain proper DO concentration in the MLE
process aerobic zones, resulting in insufficient conversion of ammonia nitrogen to nitrate and inhibition
of denitrification due to high DO concentration in the Return Activated Sludge (RAS) flow to the MLE
process anoxic zones. During normal influent loading conditions, the system was unable to maintain DO
levels in the aeration process closer than 1.0 ppm from setpoint. The DO control problem was
exacerbated during wet weather events. An analysis of the process concluded that the interaction
between the PID control loops was causing instability in the control of aeration process DO.
The following modifications to the aeration process control system were implemented:
• A specialized/proprietary DO/blower control algorithm (Dresser Roots) replaced the PID
control loops.
• Direct air flow control was substituted for the pressure control logic, basing the MOV
strategy on air flow vs. pressure.
The results of these modifications were:
• The RAS flow DO control is consistent and no longer inhibits biological denitrification.
• Aeration system energy consumption and costs are below projections.
• DO excursions are less than 0.5 ppm from setpoint.
• MOV logic is effective in minimizing blower energy consumption.
• Operator intervention (manual control of blowers and drop leg valves) is no longer required
to effect discharge compliance.
The annual electrical energy consumption reductions achieved through the implementation of
this ECM project were 1,068,700 kWh for 2007 (a 10.3% reduction), 1,464,800 kWh for 2008 (a 14%
reduction) and 1,207,600 kWh for 2009 (an 11.6 % reduction). The electrical energy savings for the first
three year following implementation of the aeration control system were $115,881 (Y2007), $155,457
(Y2008) and $136,022 (Y2009). The cost of implementing the aeration control system modification was
$200,000. The payback for this project was achieved in 1.5 years.
Evaluation of Energy Conservation Measures 8-11 September 2010
-------
Cose Study No. 7, Multiple Hearth Biosolids Incinerator Upgrade - Capacity and Fuel Efficiency
Improvements at the Washington Suburban Sanitary Commission Western Branch WWTP, Prince
Georges County, MD
The Washington Suburban Sanitary Commission's (WSSC) Western Branch WWTP is a 21.6 mgd
(average daily flow) denitrification activated sludge (DMAS) biological nutrient removal facility utilizing
methanol supplementation for biological denitrification and chemical precipitation for supplementing
biological phosphorus removal. Biosolids are thickened and dewatered using dissolved air flotation and
centrifuges, respectively, and are subsequently incinerated in two natural gas fired Multiple Hearth
Furnaces (MHF)s prior to landfill disposal. The furnaces were commissioned in 1974 and 1977 and were
originally designed to process 26 dry tons per day (dtpd) of heat treated biosolids. WSSC
decommissioned the biosolids heat treating process at the Western Branch WWTP soon after
commissioning the second MHF in 1977.
MHF fuel consumption, in many cases, is high due to the design of the furnace. "Cold" sludge is
fed to the top (hearth) of the furnace which is also the exhaust point for the furnace combustion gases.
The cold sludge, contacting the hot furnace, releases volatile hydrocarbons that do not have adequate
residence time in the furnace or exposure to adequately high temperature to be completely burned. The
result is a high hydrocarbon, smoky and odorous emission which is usually addressed by increasing the
operating temperature of the upper hearth(s) of the furnace or adding an afterburner section to
increase the final temperature of the furnace's exhaust gas stream. Both of these options increase
furnace fuel consumption. Additionally, operating the furnace at a higher temperature may also cause
slagging (melting) of the residual ash inside the furnace, resulting in higher maintenance costs. In 2001,
to comply with the promulgation of Title V and "zero visiobe emissions" requirements of the Clean Air
Act, the capacity of the MHFs at WSSC was reduced to 12 dtpd and external afterburners were installed,
which increased natural gas consumption.
Many furnaces that are now employed to incinerate biosolids are equipped with flue gas
recirculation and waste heat recovery systems integral to the design of the furnace. Flue gas
recirculation controls air emissions while allowing the furnace to be operated at a lower temperature.
Recovered heat energy from the furnace exhaust can be utilized to pre-heat the combustion air fed to
the furnace. Since combustion air represents a significant heat load (fuel consumption requirement) to
the furnace, pre-heating combustion air with waste heat reduces the amount of fuel required by the
furnace to effect sludge incineration. Older MHFs that are not equipped with such energy saving
features can be modified and upgraded to incorporate waste heat recovery/combustion air pre-heating,
not only resulting in fuel savings but also increasing furnace capacity and reducing maintenance.
The Western Branch MHFs were retrofitted in 2009 and 2010 with Flue Gas Recirculation (FGR)
systems that take exhaust flow from the top hearth of the furnace and re-injects it into the one of the
lower hearths. The recirculated flue gas mixes with the higher temperature combustion gases, providing
ample time and temperature to completely oxidize the volatile hydrocarbons released from the sludge
feed entering the top hearth of the NHF. This allows the furnace to run at a lower temperature (or
without exhaust gas afterburner), optimizing fuel consumption and eliminating ash slagging. The MHFs
were also retrofitted with air-to-air waste heat recovery heat exchangers that recover and utilize the
heat contained in the furnace exhaust streams (exhaust combustion air and center shaft cooling air) to
preheat the furnace combustion air, reducing the heat load to and fuel consumption of the furnace.
Circle Slot Jets were added to convey the preheated combustion air into the hearths to increase
Evaluation of Energy Conservation Measures 8-12 September 2010
-------
turbulence and air-fuel mixing. The improved convection and turbulence increases drying and
combustion rates of the furnaces, resulting in an increase in their capacity.
The modifications to the Western Branch WWTP MHFs have resulted in the following benefits:
• Increased the throughput capacity of the furnace to 17 to 19 dptd from 12 dtpd (a 42% to
58% increase), postponing the need to build new furnaces to meet growing demand.
• Reduced NOx emissions from the MHFs to meet Best Available Control technology
• Reduced natural gas consumption and cost by 320,000 therms per year (a 76% reduction)
and $400,000 per year, respectively.
Energy and maintenance savings will achieve a payback on the $4.5 million in approximately 11 years.
Cose Study No. 8, Permit Safe and Energy Smart Greening of Wastewater Treatment Plant Operations
at the San Jose/Santa Clara (CA) Water Pollution Control Plant
The San Jose/Santa Clara Water Pollution Control Plant (SJ/SC WPCP), one of the largest
advanced wastewater treatment facilities in California, serves a population of 1,500,000 people in a 300
square mile area encompassing San Jose, Santa Clara, Milpitas, Campbell, Cupertino, Los Gatos, Saratoga
and Monte Sereno. The Plant, treating an average daily flow of 107 mgd, was last upgraded from a two-
stage nitrification process to a step-feed Biological Nutrient Removal (BNR) process in 1995.
In 2008, the SJ/SC WPCP implemented the following Energy Conservation Measures (ECMs)
projects with financial assistance from the California Wastewater Process Optimization Program
(CalPOP):
• Optimization of three Plant pumping systems (Post Screening, Post Primary Settling and Post
Clarification).
• Implementation of pulsed air mixing of the WPCP's BNR process anaerobic and anoxic reactors.
• Optimization of the sludge thickening Dissolved Air Flotation (DAF) pressurization pumps.
All three ECM projects involved the development and implementation of proprietary control system
algorithms.
The Post Screening, Post Primary Settling and Post Clarification pumping systems' optimization
project resulted in electrical energy use reductions of 13.33 kW/million gallons (MG) (a 22% reduction),
19.9 kW/MG (a 23.5% reduction) and 21.6 kW/MG (a 17% reduction), respectively. Pulsed air mixing of
the BNR process anaerobic and anoxic reactors reduced natural gas consumption by 1.2 X 1011 BTU/yr (a
38% reduction) and electrical energy consumption by 4.8 X 10s kWh/yr ,a 23% reduction (aeration for
one of the two BNR trains at SJ/SC WPCP is provided by internal combustion engine driven blowers; the
blowers for the second BNR train are electric motor driven). Optimization of the operation of the DAF
pressurization pumps reduced electrical energy consumption by 1,603,030 kWh/yr (a 64% reduction).
Evaluation of Energy Conservation Measures 8-13 September 2010
-------
Testing and verification of these ECM projects by the SJ/SC WPCP's energy utility (Pacific Gas &
Electric) reported a total energy savings of $1,178,811 per year. With a total implementation cost for
these three ECM projects of $269,569, the payback for the combined ECM projects was less than 3
months.
Cose Study No. 9, Diffuser Upgrades and DO Controlled Blowers at the Waco, TX Metropolitan Area
Regional Sewer System Wastewater Treatment Facility
The Waco Metropolitan Area Regional Sewer System (WMARSS) Treatment facility is a 22.8 mgd
(average daily flow) single-stage nitrification plant with multi-stage centrifugal blowers. The facility was
experiencing difficulty achieving single stage nitrification because the existing aeration system was
unable to deliver the required oxygen to complete the nitrification reaction. As a result, the air flow rate
for the diffusers was set at a rate that exceeded the design rate of the diffusers causing them to produce
coarse bubble vs. fine bubbles, further exacerbating the inadequate transfer of oxygen into the
wastewater.
The WMARSS facility staff analyzed the problem and concluded that an upgrade to the aeration
system was necessary. Under the upgrade, the number of fine bubble diffusers in each basin was
increased from 2,800 to 3,500. In addition, a DO probe was added into each of the aeration basins'
three aeration zones (mid-way in the first and second aeration zones and at the end of the third
aeration zone). The control system was upgraded to provide automatic control based on the readings of
the DO monitoring system.
The upgrades to the aeration system cost $397,708 (total installed cost). The installation was
done by plant personnel so no outside installation costs were incurred by WMARSS. Electrical energy
savings of $331,272 were realized in the first two years and $335,907 in year 3 following the
installation/commissioning of the ECM project, resulting in a payback of 2.4 years. Between 2003 and
2008, the system reduced electrical energy consumption by an average of 4,642,741 kWh/yr (33%
reduction) representing over 2.5 million dollars in energy cost savings over this period (an average annual
energy cost savings of $423,226/yr). In addition to energy savings, labor costs have been reduced as
operators no longer are required to perform routine DO readings and associated manual blower
adjustments. Since the nitrification process is now working as designed, nitrate levels are lower in the
effluent, reducing chlorine demand in the disinfection process, and thus resulting in reduced chemical
costs for chlorine.
Evaluation of Energy Conservation Measures 8-14 September 2010
-------
Appendix A
Facility Case Studies
Case Study No. 1, Magnetic Bearing Turbo Blowers at the Green Bay Metropolitan Sewerage District De
Pere Wastewater Treatment Facility
Case Study No. 2, Turblex Blowers and Air Flow Control Valves at the Sheboygan Regional Wastewater
Treatment Plant
Case Study No. 3, Upgrade from Mechanical Aeration to Air-bearing Turbo blowers and Fine Bubble
Diffusers at the Big Gulch Wastewater Treatment Plant
Case Study No.4, Optical DO Sensor technology and Aerator Rotor VFD Control at the City of Bartlett
Wastewater Treatment Plant
Case Study No.5, Advanced Aeration Control for the Oxnard, CA Wastewater Treatment Plant
Case Study No. 6, DO Optimization Using Floating Pressure Blower Control in a Most Open Valve
Strategy at the Narragansett Bay Commission Bucklin Point WTF
Case Study No. 7', Multiple Hearth Biosolids Incinerator Upgrade-Capacity and Fuel Efficiency
Improvements at the Washington Suburban Sanitary Commission Western Branch WWTP
Case Study No. 8, Permit Safe and Energy Smart Greening of Wastewater Treatment Plant Operations at
the San Jose / Santa Clara (CA) Water Pollution Control Plant
Case Study No. 9, Diffuser Upgrades and DO Controlled Blowers at the Waco Metropolitan Area Regional
Sewer System Wastewater Treatment Facility
-------
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 1
Magnetic Bearing High Speed Turbo Blowers
Green Bay Metropolitan Sewerage District - De Pere Facility
De Pere, Wisconsin
Facility Size: 14.2 mgd design, 8 mgd average daily flow
Figure 1: Aerial View of the GBMSD - De Pere Wastewater Treatment Facility
(Photo provided courtesy of the Green Bay Metropolitan Sewerage District)
Facility/Process Description:
The Green Bay (Wl) Metropolitan Sewerage District's (GBMSD) De Pere Wastewater Treatment
Facility (WWTF) serves the City of De Pere, portions of the Village of Ashwaubenon and portions of the
Towns of Lawrence, Belleview, and Hobart. GBMSD acquired ownership of the De Pere WWTF from the
City of De Pere on January 1, 2008.
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
The original circa mid-1930's plant (a primary treatment facility with sludge digestion) was
upgraded in 1964 to an activated sludge process, with chlorination for disinfection. In the late 1970s,
there was a major upgrade to the facility (which represents the current operational scheme), including a
two stage activated sludge process with biological phosphorus removal, tertiary filtration (gravity sand
filters), solids dewatering with incineration, and liquid chlorine disinfection.
Influent data for the De Pere WWTF are presented in Table 1.
Table 1: Profile of De Pere WWTF Influent Data (Y2009)
Parameter
Flow (mgd)
BOD (Ibs/day)
TSS (Ibs/day)
Ammonia-N (Ibs/day)
Phosphorus (Ibs/day)
Daily Average
8
29,070
18,587
Not Monitored
307.5
In 1997, additional upgrades to the facility were initiated, beginning with UV disinfection
replacing the liquid chlorine system. The chlorine disinfection system is currently maintained as a back-
up system. Several other major upgrades included: replacement of the coarse influent screens with fine
screens (1998-1999), renovation of the multi-media tertiary filtration system to a single media U.S. Filter
Multiwash air scour system (1999-2000), and a solids handling upgrade which included installation of
two gravity belt thickeners (replacing dissolved air flotation) and the addition of two filter presses
(2001-2002).
Figure 2 presents the process flow diagram for the GBMSD - DePere WWTF, a two-stage
activated sludge treatment plant with tertiary filtration.
Influent to the plant undergoes fine screening and is subsequently pumped to preliminary
treatment (grit removal followed by grease removal, utilizing two 50 ft X 50 ft clarifiers with
grease/scum collection). The influent pump station consists of four 150 hp, 10 mgd pumps. Screenings
are disposed in a landfill. Grit, oil and grease removed in preliminary treatment units are also disposed
in a landfill.
Biological treatment is conducted in two serial stages, each with a 1.1 mgd anaerobic zone (for
phosphorus removal) followed by a 2.2 mgd aeration zone. Approximately 100% of the mixed liquor
suspended solids from the aeration zone is recycled to the anoxic zone. Aeration is provided by six
(each), 6000 scfm, 330 hp turbo blowers for the 1st stage aeration process and three (each), 4000 scfm,
250 hp multi-stage centrifugal blowers for the 2nd stage aeration process.
The first stage biological treatment is followed by clarification (two each, 100 ft diameter, 13.7 ft
side water depth clarifiers (one on line for each aeration basin)). Clarifier effluent from the first stage
biological treatment process can be further treated in the second stage treatment process. However, all
wastewater is currently treated only in the first stage biological process. The second stage of biological
treatment is not currently utilized since it is not required to achieve discharge compliance. Biological
treatment is followed by three 125 foot diameter, 10.9 foot side water depth clarifiers. Clarifier effluent
Evaluation of Energy Conservation Measures 2 September 2010
De Pere (Wl) WWTF Case Study
-------
(RAS)
2nd Stage
Aeration Basin
(Biological Treatment)
Raw Sewage
Influent
River
Fine Screening
Pump Station
Preliminary Treatment 1 st Stage
Grit & Grease Aeration Basin
Removal i (Biological Treatment)
i rtemovai i
Intermediate
Clarification
(WAS)
Tertiary
Sand Filters
UV Disinfection
(WAS)
Grit to
Landfill
Grease to
Landfill
Thickened Sludge
Conditioning
Waste Activated Sludge
Plate & Frame
Filter Press
(Dewatering)
Ash to Landfill
Incineration
Sludge
to Landfill
Belt Filter Press
(Dewatering)
Online May, 1978 to Present
Design Flows:
Average Dry - 9.5 MGD
Design Flow-14.2 MGD
Max Hourly Dry - 23.8 MGD
Max Hourly Wet - 30.0 MGD
Figure 2: GBMSD - De Pere WWTF PrOCeSS FlOW Diagram (graphic provided courtesy of Green Bay Metropolitan Sewerage District)
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
is polished by tertiary sand filtration and disinfected using UV prior to discharge. During periods of high
flow, UV disinfection is supplemented by disinfection with liquid chlorine.
Clarifier underflow (WAS - waste activated sludge) from biological treatment undergoes one of
two dewatering processes. Approximately 75% of the WAS undergoes thickening (two each, 2 m gravity
belt thickeners), chemical conditioning (lime and ferric chloride), dewatering (two each, 1.5 m X 2 m
plate and frame filter press) and incineration (18.75 foot diameter, 7 hearth, 7,500 Ib/hr multiple hearth
incinerator). The incinerator ash is disposed in a landfill. The balance of the WAS is chemically
conditioned with polymer and dewatered in two each, 2 m belt filter presses. The dewatered sludge is
disposed in a landfill. Filtrate from sludge thickening and dewatering operations is returned to 1st stage
biological treatment.
The most recent upgrade (2003-2004) replaced the facility's 1st stage treatment centrifugal
blowers (See Figure 3) with high-speed, magnetic turbo blowers (See Figure 4), the first installation of
this new, energy efficient technology in the country. Because the 2nd stage aeration process is currently
not utilized, only the 1st stage process blowers were replaced under the ECM project.
Figure 3: Multi-stage Centrifugal Blowers - GBMSD - De Pere Wastewater Treatment Facility
(Photo provided courtesy of the Green Bay Metropolitan Sewerage District)
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
Figure 4: Magnetic Bearing Turbo Blowers - GBMSD - De Pere Wastewater Treatment Facility
(Photo provided courtesy of the Green Bay Metropolitan Sewerage District)
Description of Energy Conservation Measures (ECMs):
In October 2004, the City of De Pere commissioned six new high speed, magnetic bearing turbo
blowers (330 hp HST Model S9000-1-H-5 manufactured by ABS, Inc.) for the facility's 1st stage aeration
process. Prior to the blower replacement ECM project, the facility's existing blowers (five each, 450 hp
multi-stage centrifugal blowers) had reached the end of their service life, requiring an extensive and
expensive rebuild or replacement. An evaluation by the WWTP operations manager and their engineer
determined that replacement of the existing multi-stage centrifugal blowers with magnetic bearing
turbo blowers would meet the wastewater utility's mission of providing the highest quality of
wastewater treatment for their service area customers at the lowest cost. The new blowers would help
meet this goal by:
• Increasing the efficiency of the aeration system and reducing energy costs.
• Reducing/eliminating normal routine maintenance requirements of the aeration system.
• Reducing operating costs through better matching of blower capacity to aeration demand
(operating two to three 330 hp turbo blowers versus two to three 450 hp centrifugal blowers).
• Maintaining high efficiency over a wide range of operation, while offering a high degree of
turndown.
ECM Commissioning Date:
Six new 330 hp magnetic bearing turbo blowers were commissioned October 18, 2004 replacing
five 450 hp centrifugal blowers.
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
Description of ECM Project Drivers and Issues:
Implementation of the blower replacement project was initiated by the City of De Pere in
response to the need to address the situation in which the aeration system blowers had reached the
end of their design operating life. Other drivers for the project included requirements for increasing the
plant's capacity, reducing the amount of staff time for maintenance and control of the aeration system,
maintaining high quality effluent, and effecting energy savings. The WWTF management and their
engineer had determined that replacement of the blowers was necessary to continue providing their
customers with high quality wastewater treatment services at the lowest price.
Plant Influent and Effluent Quality
Table 2 provides a comparison of the De Pere WWTF performance prior to the implementation
of aeration system improvements (Y2003) and current (post-ECM implementation) performance.
Table 2: Monthly Average
Parameter
BOD
TSS
NH3
P
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2003
Concentration Range,
mg/L
453. 10 to 704.07
0.62 to 5. 69
9
267.43
0.66 to 3. 33
10
Notel
0.14 to 2.44
24 (summer)
34 (winter)
5.43 to 8.24
0.15 to 0.33
1
Y2009
Concentration Range,
mg/L
380.09 to 499.43
2.31 to 6.10
9
229.36 to 352.46
1.39 to 3. 35
10
Notel
0.16 to 4.14
24 (summer)
34 (winter)
4.05 to 6.12
0.1 to 0.24
1
Note 1: Influent concentration is not required to be monitored/reported as a
permit condition
Results
ECM Implementation Cost
Table 3 summarizes the implementation cost for the De Pere turbo blower ECM project:
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
Table 3: ECM Implementation Cost
Cost Category
Capital Cost (Note 1)
Installation Costs
Total Cost
Cost (in Y2004 $)
$850,000
Note 2
Note 2
Note 1: Capital cost included replacement of the plant's medium power
supply voltage system (2400 volts) to a lower voltage system (480 volts) to
provide compatibility with the new turbo blowers.
Note2: The blower replacement project was implemented as part of a larger
($2,000,000) plant infrastructure improvement project. Installation costs
exclusively associated with the blower upgrade are not available. Installation
costs for blowers are site specific and equipment specific. However, for
estimating purposes, installation costs often run 10% to 15% of capital costs.
Energy
Table 4 summarizes the De Pere WWTF electrical energy consumption and savings for the
aeration system improvement project.
Table 4: Electricity Use and Estimated Savings
Year
Annual Electrical Energy Use
Electrical Energy Cost
Rate
Annual Cost
Prior to ECM Implementation
2003
4,325,700 kWh
$0.0393/kWh
$170,000
Following ECM Implementation
2005
2,181,725 kWh
$0.0487/kWh
$106,250
Savings
2,143,975 kWh
(50% reduction)
$63,758
(38% reduction)
Payback Analysis/Benefits
The blower replacement project did not focus solely on investment payback, but weighed
heavily on energy conservation, full automation of the aeration process while maintaining high-quality
effluent, ensuring protection of the environment, and gaining equipment dependability for the plant
operation. The old aeration system experienced frequent blower surging when multiple blowers were in
operation, requiring that the aeration system be operated in the manual mode. A simple payback
analysis is determined by dividing the available blower project cost ($850,000 from Table 3) by the
projected annual electricity cost savings following the project implementation. The electrical energy
costs savings provided by the turbo blower implementation resulted in a project payback in 13.3 years.
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
Conclusions
Factors Leading to Successful ECM Implementation/Operation
This project was unique in that the blower equipment to be installed was the first of its kind in
this country. This retrofit was intriguing and vitally important to the De Pere WWTP operation, creating
an ownership stake in the project. All stakeholders involved in this project (City officials, management,
operations staff, and the utility's engineering firm) worked as a team.
Impact on Other Operating Costs Resulting from ECM Implementation
Energy conservation (as shown in Table 4) was the most important factor, along with
the importance of the replacement of outdated and failing equipment.
In addition to energy saving resulting from this project, the following benefits were also
realized.
Labor:
Maintenance:
Maintaining the old blower equipment was labor-intensive.
Maintenance needs for the old system included greasing the centrifugal
blower motors, monitoring and filling oil levels in the blower bearing
lubrication reservoirs, changing out the inlet filters, seal replacement,
and vibration analysis on a weekly basis.
Operationally, the old system was designed for coarse air bubble
aeration. Therefore, when fine bubble diffusers were installed for
energy conservation, blower surging, (especially when multiple blowers
were in operation), became a major problem when trying to operate in
the automatic mode. As a result, operation of the aeration system
required manual control of the blowers. System demand variations
required staff to make changes to blower output many times
throughout the day.
The new High Speed Turbo Blower system is SCADA controlled, making
the operation fully automatic, reducing staff surveillance of the aeration
process.
Routine maintenance to the turbo blowers is minimal. Changing of the
inlet filters is done on an as needed basis, normally once per year,
unless outside conditions become very dusty. The location of the new
blowers (away from other plant process areas) contributed to reducing
air inlet filter maintenance. Additionally, without the presence of any
wear parts (bearings, gears, etc.), maintenance on the turbo blowers is
virtually eliminated and vibration analysis is not required for the turbo
blowers.
Evaluation of Energy Conservation Measures
De Pere (Wl) WWTF Case Study
September 2010
-------
Lessons Learned
As a result of this project and facility upgrade projects implemented subsequent to the blower
replacement, the GBMSD-De Pere WWTF management learned that developing and executing a
carefully planned program for replacing outdated and failing equipment can be accomplished without
increasing treatment costs and customer user fees.
Additionally, the blower replacement project provided other benefits and lessons that included:
• The magnetic bearing turbo blowers operate at significantly lower noise levels (75 dBA
compared to 100 dBA) and are vibration-free compared to the multi-stage centrifugal
blowers, providing a comfort benefit to wastewater treatment staff working in the blower
room. With the multi-stage centrifugal blowers, spending any extended time in the blower
room was difficult to tolerate and unsafe without hearing protection.
• Heat from the turbo blower's cooling air exhaust is recirculated to plant buildings, reducing
the demand for auxiliary heat.
• The GBMSD-De Pere WWTF was the first facility in the United States to install magnetic
bearing turbo blowers. Following a thorough investigation of the magnetic bearing turbo
blower technology, the stakeholder/project team concluded that the benefits offered by
this new cutting-edge technology far outweighed the risk.
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Michael Kersten, Operations Manager, Green Bay Metropolitan Sewerage District De Pere (Wl)
Wastewater Treatment Plant.
Dean P. Zannon, P.E., Project Engineer - Robert E. Lee & Associates, Inc., Oneida, Wl
Joseph Cantwell, P.E., Senior Engineer - Energy Systems Group, Science Applications
International Corporation (SAIC), Brookfield, Wl
References and Bibliography
Shumaker, Gerald; High Speed Technology Brings Low Costs, Water and Wastes Digest, August 2007.
Evaluation of Energy Conservation Measures 9 September 2010
De Pere (Wl) WWTF Case Study
-------
Utility Contact Information:
Michael Kersten
Operations Manager
Green Bay metropolitan Sewerage District - DePere Wastewater
Treatment Plant
315 Leonard Street
De Pere, Wl 54115
Telephone: (920) 339-4094
email: mkersten@gbmsd.org
Project Engineer Contact Information:
Dean P. Zanon, P.E.
Project Engineer
Robert E. Lee & Associates, Inc.
4664 Golden Pond Park Ct.
Oneida, Wl 54115
Telephone: (920) 662-9141
email: dzanon@releeinc.com
Evaluation of Energy Conservation Measures 10 September 2010
De Pere (Wl) WWTF Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 2
Aeration System Blower Replacement and Control Valves
Sheboygan Regional WWTP - City ofSheboygan
Sheboygan, Wisconsin
Facility Size: 18.4 MGD design, 11.8 MGD average daily flow
Figure 1: Aerial View of the Sheboygan Wastewater Treatment Plant
(Photo provided courtesy ofSheboygan Regional WWTP)
Facility/Process Description:
The Sheboygan Regional Wastewater Treatment Plant (WWTP) serves approximately 68,000
residential customers in the cities of Sheboygan and Sheboygan Falls, the Village of Kohler, and the
Town(s) of Sheboygan, Sheboygan Falls, and Wilson. The plant was originally constructed in 1982 as a
conventional activated sludge plant using turbine aerators with sparger rings. In 1990, the plant was
Evaluation of Energy Conservation Measure
Sheboygan (Wl) WWTP Case Study
September 2010
-------
upgraded to include a fine bubble diffused air system with positive displacement blowers. From 1997
through 1999, additional improvements were made to the facility to implement biological nutrient
removal and to the bar screens, grit removal facilities, bio-solids storage tanks, and the primary and
secondary clarifiers. The plant currently operates as an 18.4 MGD biological nutrient removal plant with
fine screens, grit removal, primary clarification, biological nutrient removal, activated sludge aeration,
secondary clarification, disinfection, anaerobic sludge digestion, gravity belt sludge thickening, and
liquid (6% solids) bio-solids storage. Table 1 provides average daily influent data for the plant. Figure 2
provides a process flow diagram of the plant treatment scheme.
Table 1: Profile of Sheboygan WWTP Influent Data (Y2009)
Parameter
Flow (MGD)
BOD (mg/L)
TSS (mg/L)
Ammonia-N (mg/L)
Phosphorus (mg/L)
Da My Average
11.78
175
203
Not Monitored
5.7
Influent to the plant goes through two automatic self cleaning fine screens. A 20 feet diameter
cyclone separator removes grit before the wastewater enters primary clarification. Primary clarification
is provided by four primary clarifiers. Secondary biological treatment is conducted in six basins. The first
two basins are anaerobic to provide phosphorus removal. They are configured with baffles in an "N"
pattern. The remaining 4 basins are currently aerated using two Turblex blowers. Following aeration,
secondary clarification is provided by 4 clarifiers. Return activated sludge (RAS) from the clarifiers is sent
to the anaerobic zone. A portion of the RAS is conveyed upstream of the primary clarifier. Plant effluent
is disinfected with chlorine and is then dechlorinated before discharge to Lake Michigan.
The combined primary and secondary sludge underflow from the primary clarifier (waste sludge)
is sent to 3 primary anaerobic digesters. From the primary digesters the sludge flows to a single
secondary anaerobic digester. Methane from the digesters is used to provide heat to the digesters as
well as fuel for ten 30 kW microturbines that provide electricity to the plant. Two belt thickeners, (one
at 2 meter, and one at 3 meter) increase the solids content of the digested sludge from 2.5 percent to 6
percent solids. Digested, thickened sludge is held in two storage tanks before being land applied.
Evaluation of Energy Conservation Measure
Sheboygan (Wl) WWTP Case Study
September 2010
-------
Influent Flow
BOO
TSS
Phosphorus
MGD 11.775
ma/I 175
mg/l 203
mg/L 5.67
High Strength Waste (HSW) GPD 30.000
BOU mg/l -40.000
TSS mg/l -10.000
mj/L -2.000
Disinfection Unit
Effluent Flew MGD
CBOD mg/l
TSS
Phosphorus mgfl.
NH3-N mg/l
11775
3.10
44
0,61
Liquid If."!: SulhM
Figure 2: Sheboygan Wastewater Treatment Plant Process Flow Diagram
(graphic provided courtesy of Sheboygan Regional WWTP
Evaluation of Energy Conservation Measure
Sheboygan (Wl) WWTP Case Study
September 2010
-------
Description of Energy Conservation Measures (ECMs):
The Sheboygan plant implemented improvements to its aeration system in order to provide
better dissolved oxygen (DO) control and to replace failing blower equipment. The upgrade consisted of:
• Replacing the four 250 HP positive displacement blowers with two single-stage centrifugal
blowers with inlet guide vanes and variable outlet vanes. Specifically the blowers were Turblex®
model KA5 SV-GL210 blowers equipped with 350 HP Premium Efficiency Motors.
• Replacing the DO blower controls
• Upgrading the SCADA system
• Installing air control valves on the headers to the individual aeration basin (AUMA valve
actuators and DEZURIK butterfly valves were used on the headers of the 6 aeration basins).
• Upgrading the PLC programming for the blowers.
ECM Commissioning Date:
The Turblex® blowers were installed in the summer of 2005, and the aeration basin header
control valves were installed in the spring of 2009.
Description of ECM Project Drivers and Issues:
Prior to 2005, the Sheboygan plant was operating its aeration system using four 250 HP (each)
Gardner Denver positive displacement blowers (installed in 1990). During the summer months, two
blowers were required to provide sufficient aeration, with the remaining two as standby. In 2005, one of
the blowers failed. This prompted an investigation of the remaining blowers, the results of which were
that all three of the remaining operational blowers would require total rebuild. The plant managers
determined that two new Turblex blowers with larger, energy efficient motors would allow a single
blower to meet year round aeration needs while saving energy and allow the second blower to be used
for standby (i.e., the four 250 HP positive displacement blowers could be replaced with two 350 HP
(each) centrifugal blowers).
Following commissioning of the Turblex blowers, the plant operators experienced difficulty
controlling DO in the individual aeration basins. DO levels could reach as high as 6 mg/L during evening
hours and during the winter months, wasting blower output and energy. In the spring of 2009 the plant
installed air flow control valves on the headers to each aeration basin to control DO levels in the basins
to match aeration requirements and to decrease wasted blower output and energy consumption. PLC
programming was also upgraded to provide improved control of the DO levels through automatic
operation of the air flow valves and blowers.
Plant Influent and Effluent Quality
Tables 2a and 2b show the influent and effluent qualities both before and after the
implementation of the ECMs.
Evaluation of Energy Conservation Measures 4 September 2010
Sheboygan (Wl) WWTP Case Study
-------
Table 2a: Monthly Average
Parameter
BOD/CBOD1
TSS
NH32
P
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2003 Monthly Average
Concentration, mg/l
246
12
30
244
6.1
30
Not measured
2.43
N/A
5.96
0.75
1.0
Y2009 Average
Concentration, mg/l
1751
3. 11
251
203
4.4
30
Not measured
2.862'4
232
4.7
0.6
1.0
Notes:
1. Effluent BOD limit changed to CBOD limit on October 1, 2005.
2. NH3 limit effective April 1, 2009
3. NH3 monitored weekly
4. NH3 monitored weekly
Table 2b: Daily Maximum
Parameter
BOD/ CBOD1
TSS
NH3
P
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Y2003 Daily Maximum
Concentration, mg/l
420
64
1650
63
Not measured
192
11.8
4.5
Y 2009 Daily Maximum
Concentration, mg/l
3971
121
872
12
Not measured
16.43
9.8
2.2
Notes:
1. Effluent BOD limit changed to CBOD limit on October 1, 2005.
2. NH3monitored weekly
3. NH3monitored daily
Evaluation of Energy Conservation Measures
Sheboygan (Wl) WWTP Case Study
September 2010
-------
Results
ECM Implementation Cost
Table 3 summarizes the implementation costs for the new blowers and motors. Table 4
summarizes the costs for the air control valves. The system received a Focus on Energy Grant that offset
a portion of the costs of the blowers. Focus on Energy is a quasi-governmental agency in Wisconsin
which distributes grants for electricity conservation. The source of this funding is a tax levied on electric
utility bills.
Table 3: Blower ECM Implementation Cost
Cost Category
Capital Cost
Installation Costs (Note 1)
Focus on Energy Grant
Total Cost
Cost (in Y2005 $)
504,000
286,000
-17,000
773,000
Table 4: Control Valve ECM Implementation Cost
Cost Category
Capital Cost
Installation Costs (Note 1)
Total Cost
Cost (in Y2009 $)
60,000
68,000
128,000
Note 1: The installation costs for the blower and control valve ECM projects
included modifications to the existing blower building to pull in outside air,
installing new electrical conduit and larger diameter wire to accommodate the
increased blower motor horsepower, installing new soft start controls and
cabinets, installing valve actuators on the discharge valves required for the
blower start-up sequence and modifications done to the aeration basin air
piping to install individual basin air flow control valves and the air blow-off
channel air.
Energy
Table 5 summarizes the electricity savings from the two components of the aeration system
upgrade ECM project. The utility estimated an average reduction in annual energy costs of $25,644
following commissioning of the Turblex blowers (for the years 2006 through 2008), representing an
average reduction in annual electrical energy consumption of 358,000 kWh over this period. Based on
the three previous years' average annual energy cost savings, the implementation of the air control
valves resulted in an additional energy cost savings of $38,245 for 2009, representing an additional
reduction in annual energy consumption of 459,000 kWh.
Evaluation of Energy Conservation Measures
Sheboygan (Wl) WWTP Case Study
September 2010
-------
Table 5: ECM Implementation Electrical Energy Savings
Year
Energy Consumption and Savings
kWh Used
kWh Annual Reduction
Energy Costs and Savings
Rate ($0.00/kWh)
Annual Savings
Pre ECM Implementation
2004
2,760,000
Baseline Year
$0.0538
Baseline Year Cost = $148,888
Post ECM Implementation
20061
20071
20081
20092
2,402,000
2,402,000
2,402,000
1,943,000
358,000 (13%)
358,000 (13%)
358,000 (13%)
817,000 (30%)
$0.0665
$0.0720
$0.0764
$0.0782
$23,807
$25,776
$27,350
$63,889
Note 1 : Electrical energy savings, from blower upgrade only, estimated by utility - blower electrical energy consumption is not sub-metered.
Note 2: Electrical energy savings from blower upgrade and air control valve combined. , estimated by utility - blower electrical energy
consumption is not sub-metered.
Source: Estimated annual energy cost savings provided by Sheboygan WWTP Superintendent
Payback Analysis/Benefits
The ECMs presented in this case study were part of a larger plan implemented by the Sheboygan
WWTP management to become energy self sufficient. The facility installed 30 kW microturbines in 2006
that allow it to burn biogas from the anaerobic digesters to provide electricity and heat to the plant. In
conjunction with the microturbine implementation, the plant has undertaken various energy
conservation measures to reduce energy consumption and increase the percentage of the plant's
electrical power that can be supplied by the microturbines.
The plant superintendent estimates that the Turblex blowers have a payback period of 14 years
including the avoided cost of rebuilding the positive displacement blowers in the payback analysis.
Installing the control valves result in a shorter payback period compared to the blowers. Although there
is less than a year's worth of operating data for the air flow control valves, the initial Y2009 data show
an additional $38,245 decrease in electricity costs (from the average savings of the previous three years
from the blower replacement). Extrapolating this figure gives a payback period of less than 4 years for
the air control valves. If the costs and energy savings of both the air control valves and blowers are
taken together and the 2009 energy cost savings are taken as typical, the payback period is 14 years.
Although the payback period for this ECM project is longer than 10 years, the project was a
significant component in the utility's objective of reducing the facility's electrical power demand toward
achieving the status of meeting total plant electrical demand by on-site generation using digester gas
fueled microturbines.
Conclusions
Factors Leading to Successful ECM Implementation/Operation
The facility staff took a proactive approach to saving energy and reducing its dependence on
electric utility purchased power. Staff evaluated and continues to evaluate the energy efficiency of all
projects instead of implementing the least capital cost fix for addressing failing equipment. The control
valves significantly improved both the resultant energy cost savings and efficient operation of the new
blowers. Controlling the air flow and eliminating wasted blower output was essential to realizing the full
potential of the new blower equipment.
Evaluation of Energy Conservation Measures
Sheboygan (Wl) WWTP Case Study
September 2010
-------
Impact on Other Operating Costs Resulting from ECM Implementation
In addition to the energy costs savings, the ECM project provided the following additional
benefits:
Labor:
Using automatic air flow control, plant operators no longer need to make seasonal adjustments
to the aeration system valves for the individual aeration basins to control DO concentration.
Plant operators were required to make manual adjustments to the aeration system drop leg
valves as needed to maintain the appropriate dissolved oxygen (D.O.) level in the aeration
basins. In addition, twice a year at the beginning of winter and the beginning of summer when
influent water temperature changed, the plant operators spent additional time adjusting the
drop leg air valves. When the operating blower was rotated once a year, the operators again
adjusted the drop leg air valves to maintain the proper D.O. level in the aeration basins. The
adjustments to the drop leg air valve required approximately 90 man-hours annually
(~$2,250/year).
Maintenance:
Less maintenance is required on the air piping system with the new blowers. The former
positive displacement blowers caused a "hammering" effect on the air piping system creating
the need for frequent maintenance. The repairs to the leaking air header system resulting from
the hammering effect required 30 man-hours annually (~$750/year).
Lessons Learned
The plant initially postponed the installation of the control valves because of cost. Without the
control valves, DO concentrations in the individual aeration basins could not be properly controlled,
leading to waste of both blower output and energy. Installation of the control valves not only improved
process performance (by properly controlling DO concentrations in the aeration basins) but resulted in
greater energy cost savings than achieved by the blower replacement alone.
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Dale Doerr, Wastewater Superintendent, City of Sheboygan
Ron Hicks, Maintenance Supervisor, City of Sheboygan
References and Bibliography
Evaluation of Energy Conservation Measures 8 September 2010
Sheboygan (Wl) WWTP Case Study
-------
Utility Contact Information:
Dale Doerr
Wastewater Superintendent
Sheboygan Regional Wastewater Treatment Plant
3333 Lakeshore Drive
Sheboygan,Wl 53081
Telephone: 920-459-3464
email: Dale.doerr@sheboyganwwtp.com
Evaluation of Energy Conservation Measures 9 September 2010
Sheboygan (Wl) WWTP Case Study
-------
This page left intentionally blank.
Evaluation of Energy Conservation Measures 10 September 2010
Sheboygan (Wl) WWTP Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 3
Upgrade from Mechanical Aeration to Air-Bearing Turbo Blowers and Fine Bubble
Diffusers
Big Gulch Wastewater Treatment Plant
Mukilteo Water and Wastewater District
Mukilteo, Washington
Facility Size: 2.6 mgd design, 1.45 mgd average daily flow
Figure 1: Aerial View of Big Gulch WWTP
(Photo courtesy of MapQuest - www.maDauest.com]
Facility/Process Description:
The Big Gulch WWTP provides wastewater treatment service for 22,455 people residing in portions
of the City of Mukilteo and Snohomish County (Washington). Originally constructed in 1970, the WWTP
consisted of a coarse bar screen and single oxidation ditch using brush rotor aerators, followed by a
secondary clarifier and chlorine disinfection. Between 1989 and 1991, the Big Gulch WWTP underwent
significant upgrades including the following:
• New headworks with a grit removal channel
• Influent screw pumps
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
September 2010
-------
• Selector tank
• Second oxidation ditch
• Third secondary clarifier
• Aerobic sludge holding tanks within a rotary drum thickener
• Sludge return piping.
• Scum and waste activated sludge pumps
• Sludge pumps
• Sludge dewatering belt filter press
• Chlorine contact chamber
Subsequent to the 1991 facility upgrade, the following upgrades to the treatment plant were
implemented:
• Influent screening (perforated-plate fine screens)
• Submersible mixers (in the oxidation ditches)
• UV disinfection (replacing chlorine disinfection)
To address a need for additional oxidation ditch aeration capacity to handle intermittent increases
in BOD loading, the aeration system in both ditches was upgraded with fine bubble diffusers and
automatically controlled turbo blowers. As a result of upgrading the aeration system from mechanical
rotors to automatically controlled turbo blowers and installing the diffused air system, the Big Gulch
WWTP realized an incremental savings in energy cost, as detailed in Table 5 of this case study.
Influent data for the Big Gulch WWTP are presented in Table 1.
Table 1: Profile of Big Gulch WWTP Influent Data
Parameter
Flow (mgd)
CBOD (mg/L)
TSS (mg/L)
Average
1.68
217
255
Minimum
1.21
116
131
Maximum
2.40
462
398
Source: Data provided by Big Gulch WWTP
Note: Influent data from January 2004 to August 2010
Figure 2 presents the process flow diagram for the Big Gulch WWTP, an activated sludge treatment plant
with UV disinfection
Influent to the plant passes through a perforated-plate mechanical fine screen (rated capacity of
6.5 mgd) into a gravity grit channel. Effluent from the grit removal system is returned to the headworks
and grit is sent to the dumpster.
Degritted influent, combined with return activated sludge (RAS) from the secondary clarifiers
and filtrate from the sludge dewatering belt filter press, is lifted to the selector mixing basin using the
two influent screw lift pumps (3.83 MGD capacity, each). Selector mixing basin effluent is conveyed to
the oxidation ditches via overflow channels equipped with adjustable weir gates to distribute the flow to
the ditches (40% to Oxidation Ditch A and 60% to Oxidation Ditch B). The two oxidation ditches,
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
September 2010
-------
operating in parallel and providing a combined 18-hour hydraulic residence time, are followed by three
secondary clarifiers.
Effluent from the secondary clarifiers is conveyed to the UV disinfection system. The UV system
consists of 96 lamps and provides 35 mJ/cm2 at a peak flow of 8.7 MGD (based on 60% UV
transmittance). The UV disinfection system produces an effluent with fecal coliform counts below the
facility's permit limit of 200 colonies/100 ml (monthly average).
Waste activated sludge and scum from the secondary clarifiers are transferred via a rotary lobe
pump to a pair of two-cell aerobic sludge holding tanks for aerobic digestion, producing Class B
biosolids. In 2006 the aerobic sludge digestion system was upgraded with fine-bubble air diffusers and
positive displacement blowers. Sludge is thickened through either settling in the aerobic sludge holding
tanks or through rotary drum thickening. In 2007, the rotary drum sludge thickener was installed to
increase digestion capacity. Digested sludge is dewatered using a gravity belt dewatering press and the
dewatered sludge is transported for land application.
Table 2 provides additional detail on the activated sludge process.
Evaluation of Energy Conservation Measures 3 September 2010
Big Gulch (WA) WWTP Case Study
-------
Table 2: Big Gulch Activated Sludge System Overview
Activated Sludge System Component
Description
Oxidation Ditch A
• Constructed in 1970
• 640,000 gallons
• Receives/treats approximately 40% of plant flow
Oxidation Ditch B
• Constructed in 1991
• 1,070,000 gallons
• Receives/treats approximately 60% of plant flow
Fine Bubble Diffuser Aeration System
(Note 1)
Installed in 2008 (Ditch A)
Installed in 2009 (Ditch B)
Aeration provided by three, high-speed turbo
blowers
Horizontal momentum maintained by submersible
mixers
Monitoring and Control System (Note
1)
Dissolved oxygen (DO) and Oxidation Reduction
Potential (ORP) probes located in Ditch A and Ditch
B
Controls blower air flow to oxidation ditches
(DO/PLC)
Provides anoxic phase zone DO control for nitrate
reduction (ORP/PLC)
Secondary Clarifier 1
• Constructed in 1970
• Diameter = 58 ft, Sidewater depth = 9 ft
• Center feed, peripheral withdrawal (incorporated in
1990s)
Secondary Clarifier 2
• Constructed in 1980s
• Diameter = 54 ft, Sidewater depth = 9 f t
• Peripheral feed, center weir withdrawal
Secondary Clarifier 3
• Constructed in 1991
• Diameter = 54 ft, sidewater depth = 13 ft
• Center feed, peripheral withdrawal
Note 1 - These components of the activated sludge system are part of the ECM described in detail in
this case study.
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
September 2010
-------
OUT-HELL TD
PD^Ea
5QLHD
OLYMPUS TERRACE SE1ER DISTRICT
TfiBTETOlTEH THSiTHSKT PL1KT
CAPACITY BTUDY
HGUHB 5S-S
ESEHHC VHTP FKOCI53 FTJOIT DIAGRAM
Figure 2: Big Gulch WWTP PrOCeSS FlOW Diagram (graphicprovided courtesy of Mukilteo Water and Wastewater District)
5 September 2010
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
-------
Description of Energy Conservation Measures (ECMs):
To address regulatory agency compliance notifications (and associated corrective action
recommendations) regarding the operation of the treatment plant (the treatment plant was operating
at design capacity and exceeding BOD5 and TSS influent loading rate limitations contained in the permit),
the Mukilteo Water and Wastewater District implemented improvements to the aeration system at the
Big Gulch WWTP to increase the oxidation ditch aeration capacity and provide additional treatment for
the intermittent peak BOD and TSS loadings. These improvements were based on recommendations
provided by the Washington State Department of Ecology and a March 2008 Wastewater Treatment
Plant Capacity Study and Engineering Report by the District's engineer, Gray & Osborne.
The aeration system improvements implemented by the Mukilteo Water and Wastewater District at
the Big Gulch WWTP consisted of the following:
• Replacing the existing mechanical brush aeration systems in Oxidation Ditch A and Oxidation
Ditch B with a Sanitaire fine bubble diffuser aeration system and turbo blowers. Each oxidation
ditch has one 50-HP, high speed, turbo blower (K-Turbo, TB 50-0.6S) equipped with a variable
frequency drive. A third 50-HP blower serves as a spare. A portion of the mechanical and
electrical power infrastructure for Ditch B was included in the cost reported for the Ditch A
project (although this work could not be defined as a separate line item by the utility).
• Installing DO probes and a PLC-based control system that provide automated monitoring of the
Oxidation Ditch DO concentration and automatic response control of the aeration blowers.
• Implementing an automated ORP based control system (dNOx Anoxic Control System) to detect
the occurrence of the nitrate knee in the anoxic zone (i.e., the ORP vs. time inflection point
indicating when denitrification is complete). The dNOx Anoxic Control system uses ORP
readings to detect nitrate levels during the anoxic phase. As loading to the activated sludge
system increases, the blowers are allowed to go idle, and at the time of the nitrate knee, the
blowers are automatically turned back on.
ECM Commissioning Date:
The aeration system upgrades (fine bubble diffusers, turbo blowers and controls, and blower
building) were commissioned in Oxidation Ditch A and B in 2008 and 2010 (January), respectively.
Evaluation of Energy Conservation Measures 6 September 2010
Big Gulch (WA) WWTP Case Study
-------
Description of ECM Project Drivers and Issues:
Aeration system improvements at the Big Gulch WWTP were implemented to accommodate an
increase in BOD and TSS loadings at the facility. Primary drivers for the project included the regulatory
requirements for increasing the plant's capacity and improving effluent quality. Reducing energy
consumption was a secondary consideration. Prior to the design phase of the aeration system
improvements project, the local publicly owned electric utility (Snohomish County P.U.D.) was actively
seeking ECM projects to grant funding assistance. The Mukilteo Water and Wastewater District had
already received public and regulatory agency approval to implement the aeration system ECM project
at the Big Gulch WWTP but the project had not yet been started. The aeration system improvements
ECM project that was being planned for the Big Gulch WWTP satisfied the electric utility's project
criteria and was provided a financial incentive of $39,191 (Oxidation Ditch A) and $46,594 (Oxidation
Ditch B) to help offset project costs (see Tables 4a and 4b).
As a result of the aeration system improvements ECM project implementation, the Big Gulch
WWTP has decreased their energy usage, benefited from reduced maintenance requirements, reduced
noise levels, and decreased the amount of aerosols emitted from the oxidation ditches.
Plant Influent and Effluent Quality
Table 3 provides a comparison of the WWTP's performance prior to the implementation of
aeration system improvements (Y2008) and current (post ECM implementation) performance.
According to the 2008 capacity study conducted by Gray & Osborne, Inc., the intermittent spikes in the
influent loading that led to the loading exceedances were probably caused by non-residential
(commercial or industrial) loadings. Permit level exceedances are highlighted in Table 3 below.
Evaluation of Energy Conservation Measures 7 September 2010
Big Gulch (WA) WWTP Case Study
-------
Table 3: Big Gulch WWTP Influent and Effluent Data
Year
Average
Flow
(mgd)
CBOD
NPDES Permit Limit: 3,953 Ibs/day- influent,
544 Ibs/day- effluent.
Maximum capacity based on Capacity Analysis (5,813
Ibs/day)
Request for increase in loading limit (6,039 Ibs/day)
Influent Loading
(Ibs/day)
Effluent Loading
(Ibs/day)
TSS
NPDES Permit Limit: 3,605 Ibs/day- influent,
653 Ibs/day - effluent.
Maximum capacity based on Capacity Analysis (6,082
Ibs/day)
Request for increase in loading limit (6,082 Ibs/day)
Influent Loading
(Ibs/day)
Effluent Loading
(Ibs/day)
Prior to ECM Implementation
2004
2005
2006
2007
2008
1.80
1.74
1.81
1.82
1.56
2,178
2,052
2,751
2,611
2,809
47
45
64
53
72
2,771
2,603
2,805
4,340
4,087
103
102
78
118
177
Following ECM Implementation
2009
Ditch A
2010
Ditches
A&B
1.45
1.48
3,579
3,327
117
87
3,910
4,063
258
194
Source: Data provided by Big Gulch WWTP
Note 1: Average CBOD5:BOD5 concentration ratio of 0.88 based on January 2004-June 2007 data measurements (as reported in the March 2008 Wastewater
Treatment Capacity Report by Grey & Osborne, Inc.). CBOD5:BOD5 ratio used to convert BOD5 influent permit value and request for increase in loading limit
permit value to CBOD5.
Note 2: Based on average concentrations - In 2006, the BOD5 loading limitation was exceeded for 3 months. In 2007, the TSS loading limitation was exceeded
for 5 months.
Note 3 Since a full year of data for 2010 was not available at the time of the study report, 2010 data is based on January 2010 - August 2010 operating data.
= Permit Limit Exceeded
Report on Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
September 2010
-------
Results
ECM Implementation Costs
The Ditch A project involved removing 1 aeration rotor, installing 1 turbo blower, air piping and
air diffusers. A portion of the mechanical and electrical power infrastructure for Ditch B was included in
the cost reported for the Ditch A project (although this work could not be defined as a separate line item
by the utility). The total cost of the Ditch A aeration system upgrade (including the turbo blowers,
diffusers, probes, control; capital and installation) was $487,066. Construction costs were $389,653, and
the remainder (or 25% of the total costs) were engineering and construction administration costs of
$97,413. The Big Gulch WWTP received a $39,191 grant from its electric utility (Snohomish County
P.U.D.), which was used to offset the construction costs incurred for the ECM implementation.
Implementation costs for Oxidation Ditch A are presented in Table 4a.
Ditch B (whose treatment capacity is 1.5 times the capacity of Ditch A) involved removing 4
aeration rotors, installing 2 blowers, air piping and diffusers and the construction of a blower building to
house all three blower. The total cost of the Ditch B aeration system upgrade (which included
construction costs for building housing for the three blowers) was $1,045,022. Construction costs were
$836,018, and the remainder (or 25% of the total costs) were engineering and construction
administration costs of $209,005. The Big Gulch WWTP received a $46,594 grant from its electric utility
(Snohomish County P.U.D.), which was used to offset the construction costs incurred for the ECM
implementation. Implementation cost estimates for Oxidation Ditch B are presented in Table 4b.
Table 4a: Implementation Cost Estimates for Oxidation Ditch A
Cost Category
Construction Cost
Engineering and Construction
Administration (25%)
Subtotal
Incentives (Note 1)
Total
Cost ($2007)
$ 389,653
$ 97,413
$ 487,066
($ 39,191)
$ 447,875
Note l:lncentive offered by Snohomish County P.U.D. was used to offset
Construction costs incurred for ECM implementation.
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
September 2010
-------
Table 4b: Implementation Cost Estimates for Oxidation Ditch B
Cost Category
Construction Cost
Engineering and Construction
Administration (25%)
Subtotal
Incentives (Note 1)
Total
Cost ($2007)
$ 836,018
$ 209,005
$1,045,023
($ 46,594)
$ 998,429
Note l:lncentive offered by Snohomish County P.U.D. was used to offset
Construction costs incurred for ECM implementation.
Note 2: Oxidation Ditch B upgrades included construction of buildings to
house the 3 blowers for Oxidation Ditches A and B.
Energy
Table 5 summarizes the Big Gulch WWTP electrical energy consumption and costs prior to and
following the implementation of the aeration system improvements to Oxidation Ditch A (2009) and
Oxidation Ditch A and B (2010). The last column presents an estimate of the electrical cost savings per
year at the plant.
Observed energy savings following the Oxidation Ditch A and Ditch B aeration system upgrades
was 148,900 kWh for 2010, a reduction of nearly 11% (compared to the average electricity consumption
to the years 2005 through 2008 before the ECM project implementation). At a current electricity rate of
$0.072/kWh, this translates to a total cost savings of $10,721 in 2010.
Payback Analysis/Benefits
Dividing the total project cost minus the incentive by the 2010 observed energy savings
of 148,900 kWh and rate of $0.072/KWh, the simple payback for this ECM project is 135 years. From
strictly an energy savings perspective, this project does not represent an economic benefit. The primary
driver for this project was the utility's need to replace aging and undersized aeration equipment in
Oxidation Ditch A and B as a means of addressing chronic wastewater discharge compliance issues. The
utility took this opportunity to also consider incorporating energy efficient technologies into the
treatment facility upgrade. Reducing energy consumption was not the primary motivation for
implementing the aeration system upgrades, but rather a consideration that was prioritized by the
utility when planning the required wastewater treatment facility upgrade.
While the Big Gulch ECM project does not meet the case study selection criteria for a
reasonable payback period described in Chapter 1, the project case study is a good example of energy
savings derived as a collateral benefit from a major plant upgrade and expansion. As noted earlier, the
primary objective of this project was to increase the plant's capacity to accommodate increases in BOD
and TSS loadings to improve effluent quality to comply with permit discharge limits and restore permit
compliance. Reducing energy consumption was a secondary consideration. In fact, providing additional
oxygen to satisfy the increased organic loading was expected to increase the total energy used by the
Evaluation of Energy Conservation Measures 10 September 2010
Big Gulch (WA) WWTP Case Study
-------
facility (Note: the average CBOD influent loading following the upgrade of the oxidation ditches'
aeration systems [2009 and 2010] was 3,453 Ibs/day, an increase of 40% compared to the average CBOD
loading of the five years prior to the aeration system upgrade project [2,480.2#/day for the period 2004
- 2008]). However, the replacement of the existing mechanical brush aerators in the oxidation basins
with new fine bubble diffusers and turbo blowers did result in actually lowering the overall energy used
by the Big Gulch facility. While this project resulted in a long payback period based solely on energy
savings, the benefits of increased plant capacity and returning the plant to compliance should not be
overlooked.
Using electricity consumption and cost per pound of CBOD removed, an alternative payback
analysis was conducted. At the average annual electricity cost and pounds CBOD removed for the period
2005 through 2008 of $96,692 per year and 884,760 pounds CBOD removed per year (respectively), the
electricity cost per pound of CBOD removed for this period is $0.109. For 2010, the annual cost of
electricity (based on plant operating data for the period January 2010 through August 2010) and pounds
CBOD removed are $90,478.08 and 1,182,600 pounds (resulting in a cost of $0.072 per pounds CBOD
removed). Comparing the pre-ECM and post ECM electricity cost per pound of CBOD removed results in
a cost savings $0.037 per pound of CBOD removed through implementation of the ECM project. The
energy cost savings in 2010 associated with the ECM project implementation (to remove 1,182,600
pounds of CBOD) is $43,756. With a total project cost for the Ditch A and Ditch B modifications/upgrade
of $1,446,304, the simple payback for the project using this alternative analysis is 33 years.
Evaluation of Energy Conservation Measures 11 September 2010
Big Gulch (WA) WWTP Case Study
-------
Table 5: Electricity Use and Estimated Savings based on ECM Implementation in Oxidation Ditch A and B
Year
A
Total Electricity Use
(kWh)
B
Average Flow
(mgd)
C
Electricity Use /Flow
(kWh/mgd)
D = B/C
Average Electricity Rate
($/kWh)
E
Estimated Electricity Cost Savings
($)
l°pre-ECM implementation "" °post-ECM
implementation) t
Pre-ECM Implementation
2005
2006
2007
2008
1,358,720
1,355,440
1,353,200
1,554,800
1.74
1.81
1.82
1.56
779,380
750,590
743,857
997,199
0.068
0.068
0.069
Post-ECM Implementation
2009
Ditch A
2010
Ditch A&B
1,261,600
1,256,640
1.45
1.48
867,576
849,081
0.070
0.072
$10,076
$10,721
Source: data for columns B, C and E provided by Big Gulch WWTP
Note 1: A full year of data for 2010 was not available at the time of the study report, the average electricity use from January 2010 through August 2010 was
used for a monthly projection of electricity use from September 2010 through December 2010.
Note 2: 2010 estimated electricity cost savings are based on average electricity usage prior to any ECM implementation (2005 through 2008,
before upgrades were implemented in Oxidation ditch A)
Evaluation of Energy Conservation Measures
Big Gulch (WA) WWTP Case Study
12
September 2010
-------
Conclusions
Factors Leading to Successful ECM Implementation/Operation
The WWTP manager gained the support of the engineer and design group for replacing the
surface aerators with a fine bubble diffuser system by presenting the benefits of reduced plant
maintenance that would result from the implementation of the ECM project. Additionally, Big Gulch
WWTP contacted equipment vendors and made site visits to learn how to best employ their ECM
equipment. Lastly, the WWTP contacted their local publicly owned electric utility (Snohomish County
P.U.D.) to obtain an energy audit of their existing equipment, and subsequently entered into an
agreement with the electric utility that provided incentive payments of $39,191 to help offset project
costs for Oxidation Ditch A and $46,594 for Oxidation Ditch B.
Impact on Other Operating Costs Resulting from ECM Implementation
In addition to energy saving resulting from this project, the following benefits were also realized.
Labor: Big Gulch WWTP staff used to lubricate the bearings of the surface
aerators two times per week, and change out the transmission oil twice
per year. Additionally the drive belts for the surface aerators had to be
regularly maintained or replaced. Since the turbo blowers do not
require the same level of maintenance as the rotor aerators, the WWTP
no longer has to expend staff resources for aeration system
maintenance at the same level and does not have to purchase, store, or
dispose of aerator lubrication oil (which needs to follow hazardous
waste guidelines for disposal).
Chemicals: With the aeration system automated, mixed liquor settling has
improved, and chlorine usage to control filamentous bacteria has been
reduced to an as needed basis.
Maintenance: The surface aerators used to produce a mist of aerosols that would coat
the steel columns, handrails, and grating in the area contiguous to the
oxidation ditches. These areas required cleaning on a regular basis. As
a result of replacing the surface aerators with fine bubble diffusers
(which sit on the floor of the basin, and gently produce bubbles), the Big
Gulch WWTP staff no longer has to clean up the aerosol deposits. This
upgrade has resulted in a cleaner, quieter, and safer WWTP.
Additionally, the turbo blowers in the oxidation ditches require minimal
maintenance to replace the air filters when they become dirty.
Lessons Learned
The project and the operational issues that provided the drivers for the aeration system
improvements have emphasized to Big Gulch WWTP management and operations staff the importance
of "constantly investigating new and innovative technologies. It's an exciting time for the wastewater
industry, we're able to make improvements to our wastewater treatment system and realize significant
energy savings as a result." (Source: Phone conversation with Thomas G. Bridges - Wastewater
Treatment Plant Manager, Big Gulch WWTP. February 19, 2010).
Evaluation of Energy Conservation Measures 13 September 2010
Big Gulch (WA) WWTP Case Study
-------
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Thomas G. Bridges, Wastewater Treatment Plant Manager, Big Gulch Wastewater Treatment
Facility.
Brianna Sheppard, Laboratory Analyst, Big Gulch Wastewater Treatment Facility.
References and Bibliography
Gray & Osborne, Inc. 2008. Wastewater Treatment Plant Capacity Study and Engineering Report.
March, 2008.
Utility Contact Information:
Thomas G. Bridges
Wastewater Treatment Plant Manager
Big Gulch Wastewater Treatment Facility
Mukilteo Water & Wastewater District
PO BOX 260
Mukilteo, WA 98275
Telephone: 425-355-6637
email: gilb@mukilteowwd.org
Evaluation of Energy Conservation Measures 14 September 2010
Big Gulch (WA) WWTP Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 4
Optical DO Sensor Technology and Aerator Rotor VFD Control
City of Bartlett Wastewater Treatment Plant
Bartlett, TN
Facility Size: 2.2 mgd design, 1.0 mgd average daily flow
Figure 1: Aerial View of the City of Bartlett Wastewater Treatment Plant #1
(Photo provided courtesy of the City of Bartlett Wastewater Division)
Facility/Process Description:
The City of Bartlett's Wastewater Treatment Plant (WWTP) #1, located in West Tennessee near
Memphis, serves approximately 24,000 residential customers and one school. One hundred percent of
the plant influent is domestic wastewater. The facility was originally commissioned in 1994 as a 0.5 mgd
aerated lagoon and has undergone three major expansions (in 1999, 2003 and 2005) to meet the city's
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
growing population. In 1993, the facility was upgraded to a secondary treatment facility (one oxidation
ditch [see Figure 2] and secondary clarification). In 2003, the facility was upgraded with solids handling
(aerobic digester and belt filter press). In 2005, a second oxidation ditch was added.
Figure 2: Oxidation Ditch/Aeration Rotor at the City of Bartlett WWTP #1
(Photo provided courtesy of the City of Bartlett Wastewater Division)
Influent data for the City of Bartlett WWTP #1 is presented in Table 1.
Table 1: Profile of the City of Bartlett WWTP #1 Influent Data (Y2009)
Parameter
Flow (mgd)
BOD (mg/L)
TSS (mg/L)
Ammonia-N
(mg/L)
TKN (mg/L)
Phosphorus
(mg/L)
Daily Average
1.0
130
180
Not Monitored
41
6
Figure 3 is a process flow diagram depicting the current configuration of the treatment plant.
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
Mechanical
Screening
Oxidation Ditch
Tt 1
Oxidation Ditch
#2
Clarifier
-————^^.s
^^^^n^"^
Clarifier
— «™™,$j
4
Belt Filter Press
Aerobic Digester
Plant Influent
Oxidation Ditch Influent
Clarifier Influent
Discharge to Loosahatchie River
Waste Sludge Underflow
Digested Sludge
Dewatering Filtrate Return
Dewatered, Digested Sludge to Land Application
Figure 3: City of Bartlett WWTP #1 Process Flow Diagram
(graphic provided courtesy of City of Bartlett Wastewater Division)
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
Plant influent undergoes mechanical screening followed by biological treatment in two
mechanically aerated oxidation ditches. Each oxidation ditch is equipped with three 60 HP rotor
aerators. Oxidation ditch effluent undergoes secondary clarification followed by UV disinfection prior to
discharge to the Loosahatchie River.
Waste sludge from the secondary clarifiers undergoes aerobic digestion. Digested sludge is
dewatered in a belt filter press and is then land applied as an agricultural soil amendment and fertilizer.
Description of Energy Conservation Measures (ECMs):
The City of Bartlett Wastewater Division implemented energy efficiency improvements to its
aeration system as a result of a successful demonstration project conducted at the WWTP #1 by the
utility, Tennessee Valley Authority (TVA) and two technology vendors. The aeration system
improvements consisted of the following:
• Installing InsiteIG optical DO sensor technology (Model 10) to provide reliable DO monitoring in
the oxidation ditches.
• Integrating optical DO monitoring instrumentation output (4-20 mA signal) with VFD control
(ABB variable speed motor drives) of the aeration rotor speed.
ECM Commissioning Date:
The VFD controls for the rotor aerators and optical DO sensor technology were installed in 2007.
Description of ECM Project Drivers and Issues:
Prior to implementing the aeration system's optical DO sensor technology with integrated VFD
control of the oxidation ditch aeration rotor speed, the City of Bartlett WWTP #1 was operating each of
the two oxidation ditches with two of the available three 60 hp aeration rotors (in each oxidation ditch).
A single aerator was run (at full speed, 60 Hz) continuously and the second rotor was run (at full speed,
60 Hz) during periods of peak flow (activated by a timer/clock). The third rotor was installed, never
operated in the original plant configuration, and is not currently required but is available as a backup
spare.
The objective of the demonstration project was to advance the use of optical dissolved oxygen
sensor technology coupled with variable speed drive motor controllers to achieve energy savings at
small to medium sized (< 10 mgd) wastewater treatment facilities. Funding and/or technical support for
the demonstration project was provided by the American Public Power Association's Demonstration of
Energy-Efficient Development research program and the Tennessee Valley Authority. Additional in-kind
support was provided by the technology manufacturers (InsiteIG and ABB) which consisted of personnel
to assist in the installation and commissioning of the ECM equipment and providing DO instrumentation
and VFD equipment (at no cost) during the initial demonstration trial period.
Currently and during the demonstration program (with a DO control setpoint of 1.2 mg/L in each
of the oxidation ditches), one rotor in each of the plant's two oxidation ditches operates continuously at
full speed and the second rotor's speed varies, depending upon the DO reading in the oxidation ditch.
Evaluation of Energy Conservation Measures 4 September 2010
Bartlett (TN) WWTP Case Study
-------
The VFD controls the second rotor's input electrical power frequency between 60 Hz (at full speed) and
30 Hz (at minimum speed) and rotational speed depending on the input DO reading. The second rotor
reaches full speed for only 30 to 45 minutes each day during the peak flow period. The frequency input
to the second rotor from the VFD is 30 Hz for much of the day and occasionally the VFD controlled rotor
is turned off when the setpoint DO concentration can be maintained exclusively by the primary single,
full speed rotor.
Plant Influent and Effluent Quality
Tables 2a and 2b show the influent and effluent qualities both before and after the
implementation of the ECMs.
Table 2a: Monthly Average
Parameter
CBOD
TSS
NH3
TKN
P
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2006 Monthly Average
Concentration, mg/L
160
5
20
279
12
30
not measured
0.11
5
not measured
not measured
not measured
not measured
not measured
not measured
Y2009 Average
Concentration, mg/L
130
5
20
280
12
30
not measured
0.15
5
41
10
monitor only
6
4
monitor only
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
Table 2b: Daily Maximum
Parameter
BOD
TSS
NH3
TKN
P
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2006 Daily Maximum
Concentration, mg/L
212
5
30
500
27
45
not measured
0.40
10
not measured
not measured
not measured
not measured
not measured
not measured
Y 2009 Daily Maximum
Concentration, mg/L
200
5
30
580
35
45
not measured
0.20
10
42
15
monitor only
6.5
7
monitor only
Results
ECM Implementation Cost
Table 3 summarizes the implementation costs for the optical DO sensor technology and the
aeration rotor VFD motor speed controls.
Table 3: ECM Implementation Cost
Cost Category
Capital and Installation
Costs - Optical DO Sensor
Technology
Capital and Installation
Costs -VFD
Total Installed Cost
Cost (in Y2007 $)
$ 3,500
$10,000
$13,500
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
Energy
Table 4 summarizes the electricity energy consumption and costs prior to and following
implementation of the aeration system ECM and energy savings. Implementation of the aeration system
control ECM realized reductions of 13% in KWh per year consumed, 39% in peak demand and 22% in
annual electrical energy cost.
Table 4: Electrical Energy Cost and Savings
Energy Consumption
• KWh/day
• KWh/year
• Peak Demand, kW
Total Annual Energy Savings
Energy Costs
• (@$0.05/kWh)
• Peak Demand Charge
Total Energy Cost
Energy Cost Savings
Electrical Energy Consumption
andCostsY2006
(Rotor Controls w/Timers)
1,553
566,845
130
$28,342/year
$14,227/year
$42,569/year
Electrical Energy Consumption and
Costs Y2008
(Optical DO/VFD Rotor Controls)
1,356
494940
79
71,905 kWh/year (13%)
$24,747/year
$ 8,646/year
$33,393/year
$ 9,176/year (22%)
Source: City of Bartlett Wastewater Division Manager
Payback Analysis/Benefits
At an annual energy savings of $9,176 per year and ECM implementation cost of $13,500, The
ECM project at the Bartlett WWTP #1 realized a payback in less than 1.5 years.
Conclusions
Factors Leading to Successful ECM Implementation/Operation
The collaborative effort by the project team and stakeholder interest in the demonstration of
this technology/ECM resulted in a successful demonstration of energy savings leading to full scale
operation with continuing energy savings results.
Impact on Other Operating Costs Resulting from ECM Implementation
In addition to the energy costs savings, the ECM project provided the following additional
benefits:
Labor:
Prior to implementing the aeration system ECM, manual monitoring of the DO
concentration in the oxidation ditches required an operator's attention for approximately 1
Evaluation of Energy Conservation Measures
Bartlett (TN) WWTP Case Study
September 2010
-------
hour/day (260 hours per year) at an associated labor cost of $4,680 per year. This requirement
has been eliminated by automatic DO monitoring.
Maintenance:
The InsiteIG DO sensor requires no periodic maintenance other than monthly inspection and
rinsing with a garden hose and annual calibration. The annual cost associated with this
maintenance activity is approximately $200/year.
Lessons Learned
VFDs provide a soft start to the aeration rotor motors which should extend the operating life of
the motors.
Additionally, plant personnel learned that small changes in process control can lead to large
savings in energy costs to the City.
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Larry Gamblin, Wastewater Division Manager, City of Bartlett, TN
References and Bibliography
Brogdon, et. al., Enhancing the Energy Efficiency of Wastewater Aeration, WEFTEC 2009.
McEntyre, Charles, TVA Open House Presentation, Enhancing the Energy Efficiency of Wastewater
Aeration - Phase II (Bartlett, TN WWTP).
Utility Contact Information:
Larry A. Gamblin
Division Manager
Wastewater Department
City of Bartlett Wastewater Treatment Plant #1
5258 Shelter Run Lane
Bartlett, TN 38135
Telephone: 901-385-6451
email: lgamblin@citvofbartlett.org
Evaluation of Energy Conservation Measures 8 September 2010
Bartlett (TN) WWTP Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO.5
Advanced Aeration Control
Oxnard Wastewater Treatment Plant
Oxnard, California
Facility Size: 31.7 mgd design, 22.4 mgd average daily flow
Figure 1: Aerial View of Oxnard Wastewater Treatment Plant
(Photo provided courtesy of Oxnard WWTP)
Facility/Process Description:
The Oxnard wastewater treatment plant (WWTP), serves approximately 200,000 people from
the city of Oxnard (California). In the early 1970's, the WWTP was originally commissioned as an
advanced primary plant. In 1977, trickling filters were installed and in 1989, the facility was upgraded to
Evaluation of Energy Conservation Measures
Oxnard (CA) WWTP Case Study
September 2010
-------
a trickling filter-activated sludge system with an increase in capacity from 24.5 mgd to 31.7 mgd. Current
influent data for the Oxnard WWTP are presented in Table 1.
Table 1: Profile of Oxnard WWTP Influent Data
Oxnard WWTP Influent Quantity and Quality
Parameter
Flow (mgd)
BOD (mg/L)
TSS (mg/L)
Average
22.4
328
265
Daily Maximum
26.9
369
788
Figure 2 presents the process flow diagram for the Oxnard WWTP.
Influent undergoes screening followed by primary clarification. Primary clarified effluent is
distributed to two trickling filters filled with plastic media. One trickling filter is 40 ft in diameter and 26
ft deep, and the other is 100 ft in diameter and 26 ft deep. Under normal conditions, only the large
trickling filter is used. From the tickling filter, flow enters the aeration process (two basins, each
consisting of three compartments measuring 450 ft x 27 ft x 15 ft. The two aeration basins are of equal
size but only one basin is used at one time. Each compartment in an aeration basin has three individually
controlled aeration grids equipped with ceramic diffusers. In each aeration basin there are nine
dissolved oxygen meters (one per each grid), nine air flow meters (FCI Inc.), and correspondingly nine
valves that are automatically controlled using Rotork electrical actuators. In the original design, a
proprietary (Turblex Inc.) automatic DO (dissolved oxygen) control system was installed in combination
with five 350 hp Turblex blowers. Each blower is rated at maximum flow of 6950 acfm and 10 psig
pressure. Aeration is followed by secondary clarification, flow equalization and
chlorination/dechlorination. Treated effluent is discharged to the Pacific Ocean.
Primary sludge is thickened in a gravity thickener to 4.8% solids, while secondary sludge is
thickened in the dissolved air floatation units to 6.2% solids. Both primary and secondary sludge are
mixed prior to entering two digesters. Anaerobic digesters operate under methophilic conditions. Gas
from the digesters is used for electrical energy production by three gas-driven generators (500 kW
each). Typically, only two generators are used simultaneously. Digested sludge is dewatered in a belt
filter press (to 20% solids concentration) and disposed in a landfill.
Evaluation of Energy Conservation Measures
Oxnard (CA) WWTP Case Study
September 2010
-------
'
Plant Influent
Excess Bypass
Primary Sludge
Waste Activated Sludge
Return Activated Sludge
Thickened Secondary Sludge
Thickened Primary Sludge
Thickener Supernatant
Digester Sludge
Filtrate
DAF Underflow
Dewatered Sludge to Landfill
Ocean Outfall
Figure 2: Oxnard WWTP Process Flow Diagram
(graphic provided courtesy of OWWTP)
Evaluation of Energy Conservation Measures
Oxnard (CA) WWTP Case Study
September 2010
-------
Description of Energy Conservation Measures (ECMs):
The optimization and automation of the activated sludge system included the following measures:
• Installing two on-line TSS (total suspended solids) meters (InsiteIG, Inc). One meter was installed
in the mixed liquor channel, another in the RAS wet well. The TSS instrumentation provides
suspended solids concentrations of the aeration process mixed liquor and of the Return
Activated Sludge (RAS) which is a required input to the process control and optimization
algorithms implemented as part of the subject ECM.
• Replacing outdated GLI dissolved oxygen meters with optical sensor technology (InsiteIG Inc).
• Installing SRTmaster™ (Ekster and Associates, Inc) software providing real-time control of solids
retention time (SRT). The software utilizes a biological process model based control algorithm
and employs multilayer data filtration that guarantees that malfunctions of TSS or flow meters
will not lead to erroneous control actions and process upset. The software alerts operators
about both meter problems as well as changes in the patterns of process BOD loading or
migration of solids to the clarifiers. Finally, the software maintains minimum variability of
wasted solids over a day resulting in significant improvements in sludge thickening.
SRTmaster™ receives instrumentation readings from the plant SCADA system and sends an
optimized waste sludge flow set point to the SCADA system electronically using industry
standard OPC drivers.
• Replacing the Turblex blower pressure based control software with DOmaster™(Ekster and
Associates Inc). DOmaster™ uses biological process model based algorithms instead of
traditional PID algorithms for DO control. The software also uses a data mining algorithm,
instead of pressure data as a DO control criterion, guaranteeing the lowest blower energy
consumption. Utilization of these algorithms allows precise control of DO in each of the aeration
basin compartments, minimizing energy used by blowers without aeration system oscillations.
DOmaster™ uses multilayer data filtration to guarantee reliability of automatic control even if
one of the control elements (meters or actuators) fails. The software communicates with the
plant SCADA system in the same manner as SRTmaster™, receiving instrumentation readings
and returning airflow set points to the SCADA system for each aeration diffuser grid control
valve opening and blower vane positioning.
• Using OPTImaster™ (Ekster and Associates Inc) software to optimize set points for SRT and DO
for each aeration compartment diffuser grid.
ECM Commissioning Date:
SRTmaster™ (in addition to the associated TSS and DO instrumentation) was implemented at
the Oxnard WWTP in 2003. DOmaster™ for control of the blowers was implemented in 2004 and
OPTImaster™ was implemented in 2005.
Evaluation of Energy Conservation Measures 4 September 2010
Oxnard (CA) WWTP Case Study
-------
Description of ECM Project Drivers and Issues:
Activated sludge automation and optimization ECMs were initiated to address foaming and
intermittent bulking problems, and to reduce operator workload, and reduce energy and chemicals
usage.
Plant Influent and Effluent Quality
The data in Tables 2a-2c (provided by the Oxnard WWTP Operations manager) compares the
OWWTP performance prior to the implementation of aeration system improvements (Y2002) and
current (Y2009, post-ECM implementation) performance.
Table 2a: Monthly Average
Parameter
BOD
TSS
Influent
Effluent
Monthly Limit
Influent
Effluent
Monthly Limit
Y2002 Monthly Average
Concentration, mg/L
262
17
30
221
5
30
Y2009 Average
Concentration, mg/L
3281
17
30
2651
5
30
Note 1. In 2009 Influent samples includes recycled flow.
Table 2b: Daily Maximum
Parameter
BOD
TSS
Influent
Effluent
Weekly Limit
Influent
Effluent
Weekly Limit
Y2002 Daily Maximum
Concentration, mg/L
480
74
45
370
31
45
Y 2009 Daily Maximum
Concentration, mg/L
3691
35
45
7881
11
45
Note 1. In 2009 Influent samples includes recycled flow.
Table 2c: Sludge Volume Index (SVI)
Parameter
Average
Maximum
Y2002, mL/g
165
385
Y 2009, mL/g
130
170
Evaluation of Energy Conservation Measures
Oxnard (CA) WWTP Case Study
September 2010
-------
Results
ECM Implementation Cost
Table 3 summarizes the implementation cost for the Oxnard WWTP ECM project.
Table 3: ECM Implementation Cost
Cost Category
Software cost 1
Instrumentation costs
Installation Costs 2
Total Cost
Cost (in Y2002 $)
$ 100,000
$30,000
$5,000
$ 135,000
Note 1 Due to pilot nature of the project, City contribution was
$25,000 toward software purchase.
Note 2 - Most of ECM installation was done by plant personnel.
Implementation of the control algorithms and associated
instrumentation required approximately 2 to 3 days, while the
design of the user interface required an additional 2 weeks.
Energy
Following implementation of the ECM project, the average energy usage by blowers was
reduced from 175 kW in 2002 to 140 kW in 2009. This resulted in a 306,600 kWh per year reduction or a
20% energy savings. The average electricity cost in 2009 was $0.088/kWh. The annual energy savings
attributed to the ECM implementation is $26,980 (35kW*24hr*365days*$0.088/kWh). Relatively small
cost savings can be attributed to significant additional removal of BOD by the trickling filter.
Chemicals
Based on WWTP records: by reducing polymer dosage used for sludge thickening (a benefit of
improved sludge settleability), chemical costs were reduced by approximately $7,500 a year.
Labor
Improved process monitoring and automation reduced the number of operator hours by at least
1 hour per day by eliminating sampling, frequent field measurements and manual adjustments. The
average labor cost savings resulting from this ECM are approximately $18,250 per year
(lhr/day*$50/hour*365 days per year).
The total energy savings for this ECM are $26,980 per year. Including chemical cost savings and
reduced manpower requirements, the total savings resulting from this ECM are $52,730 per year.
Evaluation of Energy Conservation Measures 6 September 2010
Oxnard (CA) WWTP Case Study
-------
Payback Analysis/Benefits
For this analysis, simple payback is determined by dividing the total project cost ($135,000 from
Table 3) by the resultant savings ($26,980 per year for energy only, $52,730 per year total). Based on
these data, the project payback period is five years considering only the electrical energy savings.
Including the chemical cost savings and labor savings in the payback analysis reduces the payback period
to approximately 2.5 years.
Conclusions
Factors Leading to Successful ECM Implementation/Operation
The Oxnard WWTP operations manager was a champion of the innovations implemented under
this ECM project and was also personally involved in integration of the Ekster's software packages with
the plant wide control system. Under his supervision, the operation staff embraced innovative ideas and
worked directly with the vendors to speed up the implementation and commissioning of new
optimization and automatic control methods. The fact that automatic control reduced operators'
workload and improved NPDES compliance has helped adaptation of new technology at OWTP.
Additional benefits from ECM Implementation
In addition to cost saving resulting from this project, the major benefit resulting from this ECM
project was improved process stability, reducing Sludge Volume Index (SVI) on average by 20% and
maximum SVI by 50% (see Table 2c). As a result, in 2009 effluent water quality never exceeded NPDES
limits (see Table 2b). In addition, foam observed periodically before this ECM implementation has not
been seen since the project was implemented.
Lessons Learned
• Operation management leadership was a key factor in the project's success.
• ECMs need to provide multiple benefits to reduce payback period and to speed up adaptation of
new technology. Benefits related to improving reliability of operation are especially valuable.
• Reliable operation of ECMs provides the necessary confidence of operating staff in new
technology.
• When it comes to automation, the control algorithms need to take into account potential
failures of control elements and ensure that these failures will not have negative impacts on
operation.
• Third party specialized automatic control software packages can be easily integrated with
SCADA control systems using modern communication protocols. Ready to use automation
software reduces algorithm design and programming costs and provides better reliability of
automated control.
Evaluation of Energy Conservation Measures 7 September 2010
Oxnard (CA) WWTP Case Study
-------
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Mark Moise, Operation Manager, Oxnard Wastewater Treatment Plant.
Borys Pastushenko, Vice President, Brown and Caldwell.
References and Bibliography
California Energy Commission Report "Development of Software for Automatic Control of Dissolved
Oxygen Concentration", Sacramento, 2004.
Alex Ekster "Golden Age", Water Environment Technology, Volume 16, No. 6, June 2004, page 62-66.
Alex Ekster, Ji Wang, "Effective DO Control is Available" Water Environment Technology, Volume 17, No.
2, October 2005, page 40-43.
Mark Moise, Mark Norris, Process Optimization and Automation Improves Reliability and Cost Efficiency
of Oxnard WWTP, Proceedings of WEFTEC, Conference and Exposition, Washington DC, 2005.
Mark Moise, Alex Ekster , Operation of a Solids Contact Tank at Low Dissolved Oxygen and Low Total
Suspended Solids Concentrations, Proceedings of WEFTEC, Conference and Exposition, San Diego, 2007.
Utility Contact Information:
Mark Moise
Operation Manager
Oxnard Wastewater Treatment Plant
6001 Perkins Road
Oxnard, CA 93033-9047
(805) 488-3517
email: Mark.Moise@ci.oxnard.ca.us
Evaluation of Energy Conservation Measures 8 September 2010
Oxnard (CA) WWTP Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 6
DO Optimization Using Floating Pressure Blower Control in a Most Open Valve (MOV)
Strategy
Narragansett Bay Commission Bucklin Point WWTF
East Providence, Rl
Facility Size: 46 mgd (dry weather)/116 mgd (dry plus wet weather) - design
23.7 mgd - average daily flow
Figure 1: Narragansett Bay Commission Bucklin Point WWTF
(Photo provided courtesy of the Narragansett Bay Commission and United Water)
Facility/Process Description:
The Narragansett Bay Commission's (NBC) Bucklin Point Wastewater Treatment Facility (WWTF)
serves a population of approximately 130,000 residing in the cities of Central Falls, Cumberland, East
Providence, Lincoln, Pawtucket and Smithfield in the Blackstone River Valley and East Providence, Rhode
Island area. The WWTF is operated for NBC under a management contract with United Water.
The Bucklin Point WWTF was originally commissioned in 1950 and has since undergone four
major upgrades. The last comprehensive upgrade of the Bucklin Point WWTF was completed in 2006, a
reconfiguration of the conventional activated sludge aeration process to a Modified Ludzak-Ettinger
Evaluation of Energy Conservation Measures
NBC (Rl) Bucklin Point WWTF Case Study
September 2010
-------
(MLE) process to effect nitrogen removal. The MLE biological treatment process is configured in four
parallel trains each consisting of three anoxic zones followed by four aerobic zones in each train.
Aeration for the aerobic stage of the MLE process is provided by three 600 hp (each) Dresser Roots
single stage centrifugal blowers, each capable of delivering 12,100 cubic feet per minute (cfm).
Prior to the Y2006 upgrade, conventional biological treatment was accomplished in the same
aeration tanks (and tank volumes) currently being used in the modified MLE process. At that time, the
four aeration trains consisted of four aerobic zones only (each train) for a total of sixteen aerobic zones.
The modified MLE process utilized the same configuration but provided for twelve anoxic zones (three
sequential tanks at the head end of the aeration train) followed by sixteen aerobic zones (four in each
train following the three sequential anoxic zones). The Y2006 upgrade provided for a fine bubble
diffusion system in place of the mechanical aerators. The additional equipment at the aeration basin
included optical DO probes and sixteen electric motor-operated butterfly valves for modulating air flow.
Each of the 16 control zones also had a flow tube and flow transmitter to provide measurement of
ACFM (Actual Cubic Feet per Minute) to each zone.
The Y2006 plant upgrade was designed with conventional aeration/blower control utilizing
individual Proportional-lntegral-Derivative (PID) loops for controlling dissolved oxygen (DO) and air flow
in each of the MLE process aerobic zones. The DO/blower control system was based on constant
discharge pressure using Most Open Valve (MOV) logic to minimize blower energy consumption by
manipulating the air delivery system's pressure setpoint (through opening and closing the air
distribution system's drop leg valves to each of the aeration system's 16 aerobic zones) in response to
DO readings in the aerobic zones
Influent data for the NBC Bucklin Point WWTF is presented in Table 1.
Table 1: Profile of the NBC Bucklin Point Influent Data (Y2009)
Parameter
Flow (mgd)
BOD (mg/L)
TSS (mg/L)
Ammonia-N (mg/L)
TKN (mg/L)
Phosphorus (mg/L)
Daily Average
23.7
155
147
15.37
25.70
4.17
Figure 2 is a process flow diagram depicting the current configuration of the treatment plant.
Influent (dry and wet weather flow) from the facility's two main sewer interceptors (the
Blackstone Valley Interceptor and the East Providence Interceptor) are collected in the facility's influent
pump station and are conveyed (using three each 100 hp, 38.7 mgd screw pumps) to preliminary
treatment for screening and grit removal (four, 40 mgd each screens with 0.75 in openings followed by
four, 40 mgd each 19 ft diameter grit vortex units). Grit and screenings are disposed in a landfill.
Primary treatment for "dry weather" flow (up to 46 mgd) follows using three circular clarifiers (102 feet
in diameter and 14 feet deep, each). Wet weather flow (i.e., influent exceeding 46 mgd) is collected,
following preliminary treatment, in two 2.5 million gallon (total volume) holding tanks. The contents of
the wet weather holding tanks are returned to the treatment plant to undergo primary and secondary
treatment once the wet weather event flow ceases. During a wet weather event, any flow that exceeds
Evaluation of Energy Conservation Measures 2 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
the capacity of the holding tanks undergoes chlorination followed by dechlorination and is discharged to
the Seekonk River.
Primary effluent undergoes biological treatment in a four train MLE process. Each train consists
of three sequential anoxic zones (0.59 million gallons each) followed by four sequential aerobic zones
(2.28 million gallons each). Anoxic/aerobic treatment is followed by six secondary clarifiers (four at 111
feet in diameter and 11 feet deep each and two at 110 feet diameter and 12 feet deep each). An
internal mixed liquor recycle carries nitrates from the aerobic zone to the anaerobic zone for
denitrification. A portion of the settled sludge from the secondary clarifiers is returned and mixed with
the influent to the anoxic zones. Secondary clarifier effluent is disinfected using ultraviolet radiation
prior to discharge to the Seekonk River.
Primary sludge underflow from the primary clarification process and Waste Activated Sludge
(WAS) underflow from the secondary clarifiers are anaerobically digested and then are dewatered in
centrifuges to produce biosolids that are recycled as compost for use in non-agricultural land
application.
Description of Energy Conservation Measures (ECMs):
The ECM implemented at the Bucklin Point WWTF is a DO/blower control system utilizing
proprietary control algorithms (developed by ESCOR, Inc. a subsidiary to Dresser Roots]) in lieu of PID
loop control allowing DO/blower control based on airflow versus pressure. Unlike the original pressure
based system, the Dresser Roots (ESCOR) system employs direct flow control of the blowers. As the DO
varies from setpoint, the required incremental changes in air flow are used to modify both aeration drop
leg air flow and blower flow. The most open valve logic directly manipulates basin air flow control valve
positions to insure that at least one valve is always at maximum position, thereby minimizing system
pressure without using a pressure setpoint. The reduced complexity makes the control more robust and
more accurate. Elimination of the pressure control loop also minimizes tuning.
ECM Commissioning Date:
In August 2006, an integrated air flow control system was implemented to provide stable
control of the aeration system blowers. This air flow control based technology replaced the facility's
pressure based aeration control system.
Evaluation of Energy Conservation Measures 3 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
Blackstone Valley Interceptor
East Providence Interceptor
Grit and Screenings to Landfill
Primary Sludge and Scum
Return Activated Sludge
" Waste Activated Sludge
" Wet Weather Flow
Centrate Return
9 Discharge to Seekonk River
10 Sludge to Beneficial Reuse
Figure 2: NBC Bucklin Point WWTF Process Flow Diagram
[graphic provided courtesy of Narragansett Bay Commission and United Water)
Evaluation of Energy Conservation Measures
NBC (Rl) Bucklin Point WWTF Case Study
September 2010
-------
Description of ECM Project Drivers and Issues:
Following commissioning of the Bucklin Point WWTF's conversion of the activated sludge
process to an MLE process in 2006, the plant experienced difficulty attaining consistent nitrogen
removal because the constant pressure based aeration/blower control system was unable to adjust to
changing process conditions and maintain proper DO concentration in the aeration basins, resulting in
insufficient conversion of ammonia nitrogen to nitrate.
The constant pressure based control system was unable to maintain DO levels in the aeration
tanks closer than 1.0 ppm compared to setpoint. This problem was exacerbated during wet weather
events. The MOV control was unable to consistently minimize the system discharge pressure resulting in
wasted energy. An analysis conducted by ESCOR determined that the interaction between the PID
control loops was causing instability in the control of aeration basin DO. The DO/blower system control
instability in turn caused the following problems:
• Biological nitrogen removal (denitrification) was being inhibited by high DO in the internal
mixed liquor recycle (IMLR) flow to the MLE process anoxic zones.
• Energy consumption and costs exceeded expectations.
• A utility rebate was being jeopardized because the constant pressure MOV logic was
ineffective.
• Plant operations staff were forced to manually intervene in the operation of the
blowers/aeration system to maintain performance and compliance.
The drivers for implementing an improved DO/blower control system were primarily to enable
the WWTF to maintain effluent Total Nitrogen levels below 8.5 mg/L (monthly average) during the
permitted seasonal compliance period (May through October) and to provide consistent nitrification and
denitrification during varying flows from wet weather events.
The ECM significantly revised the aeration system control strategy while maintaining existing
control devices by:
• Substituting specialized/proprietary DO/blower control algorithms for PID control loops.
• Eliminating pressure control in lieu of direct air flow control.
• Basing MOV logic on zone air flow control.
The results of the ECM implementation were:
• The IMLR flow DO control is consistent and no longer inhibits denitrification in the anoxic
zone.
• Aeration system energy consumption and costs are below original projections (and the
utility rebate was secured).
Evaluation of Energy Conservation Measures 5 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
• DO excursions are less than 0.50 ppm from setpoint.
• MOV logic is effective in minimizing blower discharge pressure (and associated energy
consumption).
• Operator intervention (manual control) with the aeration system is no longer required to
effect discharge compliance.
Plant Influent and Effluent Quality
Table 2 presents the monthly average influent and effluent qualities both before and after the
implementation of the ECMs.
Table 2: Monthly Average
Parameter
BOD
TSS
NH3
TKN
Total N
P
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2004 Monthly Average
Concentration, mg/L
232
14
30
143
15
30
14.819
11.526
Not Applicable Limit
23.647
14.375
Not Applicable Limit
15.614
Not Applicable Limit
4.995
1.884
Not Applicable Limit
Y2009 Average
Concentration, mg/L
155
4
30
147
7
30
15.37
0.69
(May - October) 15
25.7
2.1
Not Applicable Limit
7.95
(May -October) 8.5
4.17
2.01
Not Applicable Limit
Results
ECM Implementation Cost
Table 3 provides the installed cost (as estimated by the utility and operations management
contractor) for the implementation of the proprietary DO/blower control system.
Evaluation of Energy Conservation Measures
NBC (Rl) Bucklin Point WWTF Case Study
September 2010
-------
Table 3: ECM Implementation Cost
Cost Category
Proprietary DO control /
blower supply management
system
Installation/Commissioning
Total Installed Cost
Cost (in Y200 $f
$170,000
$30,000
$200,000
Notel: The ECM/implementation cost is estimated by NBC and United Water
Energy
Table 4 summarizes the electricity energy consumption and costs prior to and following
implementation of the aeration system ECM and resultant energy savings.
Table 4: Electrical Energy Cost and Savings
Year
A
Monthly Electricity
Use (kWh)1
B
Average Daily
Flow
(mgd)
Annual Energy
Use Reduction
(kWh)
Average
Electricity
Rate
($/kWh)3
c
Annual Electricity Cost
Savings
E - (B evaluation year ~~ ^20061 C 12
Prior to ECM Implementation
2006
864,612
0.099
After ECM Implementation2
2007
2008
2009
775,553
742,547
763,980
20.33
21.95
21.66
1,068,700
(10.3%)
1,464,800
(14%)
1,207,600
(11.6%)
0.10843
0.10613
0.11264
$115,880(11%)
$155,457 (15%)
$136,022 (13%)
1. Total facility monthly electrical energy use less UV disinfection system.
2. ECM implementation commissioned at end of 2006
3. Rate total for supply, delivery and demand
Source: NBC and United Water
Payback Analysis/Benefits
For this analysis, simple payback is determined by dividing the ECM project cost ($200,000) from
Table 3 by the electricity cost savings following project implementation. The reduced electrical energy
consumption and electricity cost savings provided by the aeration system control ECM resulted in a
payback in the seventh month (July) of the second year following commissioning of the ECM (2008), a
1.5 year payback.
Evaluation of Energy Conservation Measures
NBC (Rl) Bucklin Point WWTF Case Study
September 2010
-------
Conclusions
Factors Leading to Successful ECM Implementation/Operation
Careful evaluation and documentation of operating conditions led to an identified need to
address dissolved oxygen control after eliminating other possible sources.
Collaboration by all stakeholders (internal and external to the NBC and Bucklin Point WWTF)
resulted in a successful resolution to the problem.
Impact on Other Operating Costs Resulting from ECM Implementation
In addition to the energy costs savings, the ECM project provided the following additional
benefits:
Labor: Implementation of the blower control system ECM eliminated field
sampling/testing for aeration basin DO readings and manual manipulation of
the aeration basins' drop leg valves.
Chemicals: The more stabilized operation resulting from the implementation of the ECM
reduced sodium bicarbonate addition, as a more consistent alkalinity in the
effluent is achieved.
Lessons Learned
In larger facilities, every component has a significant impact when it is not operating efficiently.
Constant diligence to review and improve operational procedures is critical in a biological
nutrient removal process, especially during wet weather events when the process is adversely impacted.
Biological nutrient removal processes must operate within narrow parameters (those
controllable by operations staff) to achieve the best possible steady state conditions under significant
variable conditions as compared to conventional wastewater treatment facilities. Monitoring data for
the operating parameters must be timely, accurate and repeatable to ensure operational integrity
during each shift.
Professionals involved in the design and operation of wastewater treatment facilities should be
aware of the need to operate biological systems closely and respond to changes in process conditions
within short periods of time. DO control systems and strategies must be properly designed and
integrated to maintain reliability under frequent operational changes (e.g., for blowers, inlet and outlet
guide vanes and drop leg valves which are designed for frequent changes of varying nature).
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Jim McCaughey, Manager, Environmental Safety and Technical Assistance Section - Planning,
Policy and Regulation Division, Narragansett (Rl) Bay Commission
Brent Herring, Superintendent, Operations and Engineering Division, Bucklin Point WWTF /
United Water
Thomas Jenkins, P.E., Chief Engineer Wastewater Solutions, Dresser Roots, Inc.
Evaluation of Energy Conservation Measures 8 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
Utility Contact Information:
Brent Herring
Superintendent
Operations and Engineering Division
Bucklin Point WWTF / United Water
102 Campbell Avenue
East Providence, Rl 02916
Telephone: 401-434-6350 X-182
email: brent.herring@narrabav.com
Evaluation of Energy Conservation Measures 9 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
This page left intentionally blank.
Evaluation of Energy Conservation Measures 10 September 2010
NBC (Rl) Bucklin Point WWTF Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 7
Multiple Hearth Biosolids Incinerator Upgrade - Capacity and Fuel Efficiency
Improvements
Washington Suburban Sanitary Commission
Western Branch WWTP
Upper Marlboro, MD
Facility Size: 30 mgd design, 21.6 mgd - average daily flow
Figure 1: Washington Suburban Sanitary Commission Western Branch WWTP
(Photo provided courtesy of the Washington Suburban Sanitary Commission)
Facility/Process Description:
The Washington Suburban Sanitary Commission's Western Branch Wastewater Treatment Plant
(WWTP) is located in Upper Marlboro, Maryland on the Western Branch of the Patuxent River. The
facility was originally commissioned in 1966 as a five mgd primary/secondary plant utilizing anaerobic
digestion and vacuum filters to process biosolids for land application. The current 30 mgd facility serves
Evaluation of Energy Conservation Measures
WSSC Western Branch WWTP Case Study
September 2010
-------
residential, commercial and industrial users in the east-central portion of Maryland's Prince George's
County.
Since its original commissioning in 1966, the Western Branch WWTP has undergone several
significant upgrades to accommodate the service area's growing population and to implement
treatment process enhancements required to meet increasingly stringent effluent quality requirements
promulgated by the State of Maryland and USEPA. In 1974, a 15 mgd nitrification plant (Phase I) was
constructed as well as sludge incineration facilities. In 1977, a mirror image 15 mgd nitrification plant
(Phase II) was commissioned. The Phase I and Phase II nitrification plants utilized a two sludge process
with final filtration. In 1989, a denitrification activated sludge (DMAS) process was implemented to
comply with seasonal (summer) permitted nitrogen removal effluent limits (1.5 ppm NH3 and 3.0 ppm
TKN). The DMAS process uses methanol as a carbon source for denitrification. Figure 2 provides a
process flow diagram of the Western Branch WWTP.
Additional enhancements to the Western Branch WWTP are currently being designed to
optimize the facility's nitrogen removal performance (to achieve an annual average effluent nitrogen
concentration of 3 mg/L). These enhancements are scheduled to be commissioned in 2013 and include
the following:
• High Rate Activated Sludge (HRAS) Process Upgrades
o Centralized HRAS Return Activated Sludge (RAS)/Waste Activated Sludge (WAS)
Pumping System
o Scrubber Blow-Down Recycle isolation to HRAS process
o Anaerobic Zone Baffle Walls and Mixers or Plug Flow Reactor Staging
o HRAS Surf ace Wasting
o HRAS Enhanced Nitrogen Removal (ENR) Monitoring and Control Systems
• Nitrification Activated Sludge (NAS) Process Upgrades
o Centralized NAS RAS/WAS Pumping System
o Anoxic Zone Baffles Walls and Mixers
o NAS Plug Flow Baffle Walls
o NAS ENR Monitoring and Control Systems
• Denitrification Activated Sludge (DNAS) Process Upgrades
o DNAS ENR Monitoring and Control Systems
• Solids Handling Process Upgrades
o Dissolved Air Flotation Thickening Improvements
o Increased Thickened Sludge Storage Capacity
o Dual Centrifuge Operation Capability
• HRAS Bypass with Grit Removal
Evaluation of Energy Conservation Measures 2 September 2010
WSSC Western Branch WWTP Case Study
-------
Figure 2: WSSC Western Branch WWTP Process Flow Diagram
(Graphic provided courtesy of WSCC and AECOM)
Evaluation of Energy Conservation Measures
WSSC Western Branch WWTP Case Study
September 2010
-------
Description of Energy Conservation Measures (ECMs):
The ECM implemented at the Western Branch WWTP involved upgrades to the facility's
biosolids incineration Multiple Hearth Furnaces (MHFs). Commissioned in 1974, the MHFs were
designed to process (burn) 26 dry tons per day (DTPD) of heat treated biosolids. WSSC decommissioned
the sludge heat treating process soon after commissioning the MHFs. In 1996, WSSC replaced the
centrifuges to increase the capacity of the MHFs, but in 2001 the enactment of Title V and "zero visible
emissions" required reducing the capacity of the MHFs to 12 DTPD. To mitigate visible emissions, WSSC
installed external after-burners which increased the consumption of natural gas.
Pre ECM Operation
In the MHF process, the sludge was introduced into the top of the furnace. The top hearth was
also the exhaust point for the combustion gases. The "cold" sludge feed, coming into contact with the
hot furnace, released volatile hydrocarbons that did not have sufficient residence time in the furnace
nor adequately high temperature to be oxidized (burned) completely before being emitted. The result
was a high hydrocarbon content, smoky and odorous emission. This emission exhaust stream was
controlled by increasing the operating temperature of the top of the furnace and/or utilizing the
external afterburner to increase the exhaust temperature and residence time. This operating mode
resulted in high natural gas consumption. The higher operating temperature of the furnace, in turn,
created slagging (i.e., melting) of the ash inside the furnace, increasing maintenance and associated
costs (to remove slag).
Exacerbating the increase in fuel consumption, the incoming furnace combustion air entered the
furnace at room temperature. This cooled the furnace and added significant heat load (and increased
fuel consumption) to maintain furnace temperature. The hot MHF exhaust stream was cooled and
cleaned in a wet scrubber before being discharged to the atmosphere, and the heat in the exhaust
stream was lost (i.e., waste heat was not utilized).
Energy Saving Improvements
The following energy savings modifications to the MHFs were implemented by WSSC at the
Western Branch WWTP. Figure 3 is a schematic representation of the Western Branch MHF
modifications described below.
Flue Gas Recirculation
A Flue Gas Recirculation (FGR) system was installed which collects exhaust flow from the top hearth of
the furnace and re-injects it into the lower hearths. This recirculated flue gas accomplishes the
following:
• Unburned vapors and gases from hearth 1 are redirected through the burn zone in the furnace,
providing sufficient contact time and temperature to complete the hydrocarbon oxidation
process before exhausting.
• The additional air flow through the furnace tends to cool the hot hearths (reducing slagging) and
helps to heat the cooler drying hearths -stabilizing the furnace operations.
Evaluation of Energy Conservation Measures 4 September 2010
WSSC Western Branch WWTP Case Study
-------
• The high water vapor content of the recirculated gas stream (entrained from the drying zones),
reduces the production of nitrogen oxides (NOx) in the burning hearths. Stable temperatures in
an MHF due to the addition of an FGR system are also known to reduce the production of
thermal NOx.
Exhaust Waste Heat Recovery
An air-to-air heat exchanger was installed in the exhaust stream of the furnace, upstream of the
quench and wet scrubber, allowing recovery of the waste heat from the furnace exhaust. The recovered
heat is utilized to preheat the combustion air entering the furnace, reducing the consumption of natural
gas. Additionally, the center shaft cooling air exhaust (heated air) is returned to the furnace as pre-
heated combustion air.
Multiple Hearth
Furnace
Improvements
TO
CLEAN
FXHA1KT
CIRCLE SLOT
JITS
AH ffyf CT/O/t
Figure 3: Schematic of MHF Improvements at the Western Branch WWTP
(graphic provided courtesy of WSCC and AHP)
Evaluation of Energy Conservation Measures
WSSC Western Branch WWTP Case Study
September 2010
-------
Circle Slot Jets
Circle Slot Jets, a ring of small air jets located near the top of each hearth, concentric with the
center shaft of the furnace and about one-half the diameter of the furnace, were installed in the MHFs.
Pre-heated combustion air is injected downward into the hearths through the Circle Slot Jets creating an
impingement region and dual set of donut shaped vortices in each hearth. This increases turbulence and
air-fuel mixing. Simultaneously, a small portion of the required supply air is introduced (at room
temperature) into the bottom hearth to cool the ash as it exits the furnace. The result of this
modification is improved convection and turbulence which increases drying rates in the drying zone and
combustion rates in the burn zones.
ECM Commissioning Date:
In 2009, one of the facility's multiple hearth furnaces was retrofitted with flue gas recirculation, exhaust
waste heat recovery and circle slot jets to improve fuel efficiency and capacity. In 2010, the facility's
second multiple hearth furnace was similarly modified. Sub-metering of the fuel to the furnaces (single
meter) was implemented as part of the ECM project.
Description of ECM Project Drivers and Issues:
The drivers for this ECM were:
• To significantly reduce the amount of natural gas required to burn the sludge produced from the
Western Branch WWTP.
• To meet air emission requirements.
• To pay 100% of the capital cost of upgrade through energy savings.
• To increase the throughput capacity of the furnaces.
• To reduce NOx emissions to meet Best Available Control Technology regulatory requirements.
Results
ECM Implementation Cost
Table 1 provides the installed cost (for the implementation of the MHF modifications.
Table 1: ECM Implementation Cost
Cost Category
Total Installed Cost
Cost (in Y2008$)
$4,500,000
Evaluation of Energy Conservation Measures 6 September 2010
WSSC Western Branch WWTP Case Study
-------
Energy Consumption and Costs
Table 2 summarizes the energy consumption and costs (natural gas fuel) prior to and following
implementation of the aeration system ECM and the resultant energy savings provided by the MHF
modifications.
Table 2: Natural Gas Cost and Savings
Year
Natural Gas
Consumption
(therms/Year)
Gas Rate
($/therm)
Energy Cost
($/Year)
Prior to ECM Implementation
2005
420,000
1.25
$525,000
Following ECM Implementation
2009
Savings
100,000
320,000 (76%)
1.25
$125,000
$400,000
Based on the first six months of operation of the first of two MHFs to be modified, an annual
reduction of 320,000 therms of natural gas are projected for the sludge incineration operation at the
Western Branch WWTP (a 76% reduction), resulting in an annual fuel expenditure savings of $400,000
per year.
Payback Analysis/Benefits
For this analysis, simple payback is determined by dividing the total project cost ($4,500,000
from Table 1) by the natural gas fuel cost savings projection for year following the project
implementation ($400,000 per year - Table 2). The fuel costs savings provided by the MHF modifications
resulted in a project payback period of 11.3 years following commissioning (2009). This payback period
does not include the avoided cost benefit (of delaying the construction of additional incineration
capacity) provided by the increased capacity of the existing MHFs resulting from the ECM modifications.
The new upgraded MHF operates at a continual throughput of 17-19 DTPD (a 42% to 58% capacity
increase).
Conclusions
Factors Leading to Successful ECM Implementation/Operation
1. Project planning should include the condition of existing equipment and future process,
O&M impacts, as well as energy.
2. Hands-on training of multiple operators is vital to the success of newly installed equipment.
3. To obtain commitment to a new system, plant staff must be shown that upgraded
equipment improves operations and reliability.
Impact on Other Operating Costs Resulting from ECM Implementation
Emergency Sludge Hauling: MHF modifications increase the MHF capacity, reducing the need for
emergency hauling of un-incinerated sludge. The resulting savings are estimated at $100,000 -
Evaluation of Energy Conservation Measures
WSSC Western Branch WWTP Case Study
September 2010
-------
$200,000/yr. These savings, if included in the analysis of payback, result in a payback period of between
7.5 and 9 years.
Lessons Learned
1. As seasons change, the characteristics of the biosolids change, and can range anywhere from
21% solids to 29% solids. At high solids content, the MHF is almost autogenous and in this mode
the furnace operation would be better if there was an ability to add ambient air separately from
hot air on different hearths. The Circle Slot Jets, as installed currently, do not allow this
operational mode.
2. The existing condition of the MHF should be closely evaluated when considering an ECM
implementation, as repair costs can increase the overall capital cost of the project by 10-15%. If
the existing furnace needs rehabilitation, it should take place before or during an ECM
implementation. Rehabilitation becomes more difficult once Circle Slot Jets and heat exchanger
ductwork is installed.
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Rob Taylor, Energy Manager, Washington Suburban Sanitary Commission
Alan Sauvageau, Project Manager, Washington Suburban Sanitary Commission
Nick Shirodkar, Plant Engineer, Washington Suburban Sanitary Commission
Utility Contact Information:
Rob Taylor
Energy Manager
Washington Suburban Sanitary Commission
14501 Sweitzer Lane
Laurel, MD 02707-5902
Telephone: 301-206-7122
email:
rtayl or@ wsscwate r. com
Evaluation of Energy Conservation Measures
WSSC Western Branch WWTP Case Study
September 2010
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO. 8
Permit Safe and Energy Smart Greening of Wastewater Treatment Plant Operations
San Jose/Santa Clara Water Pollution Control Plant
San Jose, California
Facility Size: 167 mgd design, 107 mgd average daily flow
Figure 1: Aerial View of SJ/SC WPCP
(Photo provided courtesy of SJ/SC WPCP)
Facility/Process Description
The San Jose/Santa Clara Water Pollution Control Plant (Plant) first began operations in
1956 as a primary treatment facility. The Plant was upgraded in 1964 to secondary treatment
and again in 1979 with addition of a two-stage nitrification and filtration process. A step-feed
Biological Nutrient Removal (BNR) was implemented in 1995 which led to reduction of the
aeration energy consumption and costs, enhanced bulking control, and increased plant capacity.
The single stage BNR process has the advantage of operating two activated sludge plants in
parallel rather than in series (as was the case prior to the 1995 upgrade).
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
The Plant has capacity to treat 167 million gallons per day (mgd) and currently receives
an average influent of 107 mgd. Approximately 10 percent of the Plant effluent is reused as
recycled water for irrigation and makeup water for cooling towers. The Plant influent data are
presented in Table 1.
Parameter
Flow (mgd)
BOD (mg/L)
TSS (mg/L)
Ammonia-N (mg/L)
Average
107
298
241
31
Daily Maximum
167
512
797
54
Figure 2 presents the process flow diagram for SJ/SC WPCP.
Raw sewage entering the Plant undergoes several stages of treatment. First, the
influent passes through screening, grit removal, and primary settling. The flow then splits into
two parallel BNR plants (BNR1 and BNR2). The BNR plants consist of multiple treatment zones
with multiple aerators and clarifiers. The first compartment in each aeration basin is operated
under anaerobic conditions and the second and forth compartments are operated under aerobic
conditions. The third compartment is operated under anoxic conditions. Approximately 60% of
the influent flow and 100% of the Returned Activated Sludge (RAS) are fed to the first
(anaerobic) compartment. Approximately 40% of the influent flow is fed to the third
compartment that is operated under anoxic conditions. To maintain solids in suspension in the
anoxic/anaerobic compartments, approximately 1000 scfm of air are pumped into each of these
compartments. To minimize capital cost when the plant was upgraded from the two-stage
nitrification configuration to the BNR plant, existing coarse bubble diffusers were utilized for
mixing the anaerobic/anoxic zones versus installing new mechanical mixers.
A schematic of the BNR process is depicted in Figure 3.
Air is supplied to the BNR1 plant aeration process by internal combustion engine driven
blowers that utilize a mixture of digester, landfill, and natural gas for fuel. A by-product of the
operation of the internal combustion engines is hot water (spent cooling water) that is used for
digester heating. Air is supplied to the BNR2 plant aeration process by electric motor driven
blowers. BNR process effluent is filtered, disinfected with chlorine, and then dechlorinated prior
to discharge to San Francisco Bay.
The solids wasted from the BNR processes are thickened in Dissolved Air Floatation
(DAF) tanks. This thickened sludge is then fed to the Plant's mesophilic digesters where it
blends with the sludge from the primary clarifiers. Digested solids are stored in sludge
stabilization lagoons for up to three years and the dredged sludge from these lagoons is dried in
solar drying beds. The dried solids are then hauled to a nearby landfill and used as landfill cover.
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
Raw
Sewage
Influent
Screening
Raw Sewage
Pumps
Primary
Effluent"
Pumps
Primary
Settling
Settled Sewage
Pumps
Sludge
Thickenina
T
Sludge to Raw
Sewage Wet Well
Sludge
Digestion
Supernatant to
Raw Sewage
Wet Well
Optimized Processes
Storage Lagoons
Drying Beds
Dried
Sludge
Figure 2: SJ/SC WPCP Treatment Process Flow Diagram
(graphic provided courtesy of SJ/SC WPCP)
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
IAIR
i
OTTAD 2
^
AEROBIC
1
1
QUAD 3
^
ANOXIC
t
IAIR
IAIR
i
OTTAT) 1
ANAEROBIC rf
QUAD 4
A, T7T?f~VT?Tr~'
t
lATR
AIR
PE 60%
RAS
TV/IT CC TO Cl?*"1
CLARIFIERS
Figure 3: SJ/SC WPCP BNR Process Flow Diagram
(graphic provided courtesy of SJ/SC WPCP)
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
During the past several years, the Plant has been quite active and successful in identifying
and implementing energy saving projects without compromising effluent quality. The projects
have produced significant sustained savings in operating costs. In addition to energy savings,
financial incentives in the form of rebates from the local electric and natural gas utility, Pacific Gas
& Electric Co. (PG&E; San Francisco), helped to incentivize these projects. In many cases, the utility
rebates covered the entire cost of the projects resulting in a final implementation cost of zero.
This case study describes several energy conservation measures (ECM) projects completed
in 2008 which were partially funded by the California Wastewater Process Optimization Program
(CalPOP). The Program was administered by QuEST, Inc. (Berkeley,Ca). The ECM projects
implemented at the SJ/SC Plant consisted of the following:
Pumping Systems Optimization
The first ECM project focused on reducing energy consumption by optimizing the
operation of three of the Plant's major pump stations. The information on the optimized pump
stations is provided in Table 2.
Pump Station
Post Screening
Post Primary Settling
Post Clarification
Average flow
(mgd)
113
109
108
Total Number
of Pumps1
7
4
5
VFD-
Equipped
Motors
3
4
5
Power Use
(kWh/day)
282
384
570
Note 1: Not all pumps are operated simultaneously
The plant implemented an optimization algorithm developed by Ekster & Associates, Inc.
(Fremont, Ca) to select the proper pump operating schedule and optimize energy consumption.
This computer program utilizes field data such as pump station flows, pump discharge pressures,
wet well levels, and the power usage associated with pumps. The pertinent data was collected
using a specially designed pump testing routine. Thereafter, the software program selects the
combination of pumps and speed (for the existing variable speed motors) at each flow rate. To
assure that the global rather than local minimum power consumption is reached, the software
program utilizes two optimization algorithms in tandem (genetic and gradient reduction
algorithms) rather than a single algorithm. This methodology guarantees that the selected pumps
and speed combination for each flow regime results in the consumption of less energy compared
to any other possible combination.
Plant staff programmed the selected schedule and pump speed for each flow range into
the Plant's Distributed Control System (DCS). In addition, discharge pressures and wet well levels
were optimized by reassessing the minimum safety requirements.
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
During the implementation phase of this project, the plant compared field data to the
pump manufacturers' data. This included a comparison of the manufacturers' pump performance
curves with the experimental curves. The study revealed that some of the pumps had lost 5% - 7%
of their efficiency, probably due to age and wear. These findings reinforced the idea that pump
curves generated using field data — not manufacturer's pump curves — should be used to
develop optimized operating sequences. In addition, this effort resulted in the identification and
qualification of the pumping systems' information and data that will be used by the utility to plan
for the refurbishing and replacement of underperforming pumping system components.
BNR Process Improvements Pulse Aeration ofAnerobic/Anoxic Zones & Mixed Liquor Channels
A second ECM project implemented at the Plant involved switching the mode of air mixing
in the anoxic/anaerobic compartments of BNR plants from continuous to pulse (On/Off). This
aeration method was also applied to the Mixed Liquor Channels (MLC) of both BNR plants. Prior to
switching to the pulse air mixing mode, solids were maintained in suspension in the
anaerobic/anoxic compartments and MLCs by continuous air flow. By utilizing an Ekster and
Associates' patent-pending method, continuous air mixing was replaced by pulsed air mixing.
The implementation of this ECM required significant modifications of the aeration system.
These modifications included installation of new valves, actuators, pneumatic lines, electrical
infrastructure, and special control system programming. These modifications were required to be
completed within a six-month period due to deadlines associated with the CalPOP program. To
meet this unusually stringent schedule requirement, the Plant staff performed the conceptual and
detailed designs in-house and prepared all other pertinent documentations including the bid
packages. Plant staff also specified control valves, flow meters, actuators, and auxiliary control
elements, such as air piping for actuators, input-output units for the Plant's Distributed Control
System (DCS), etc.
Establishing the timing sequence of the activation and deactivation (i.e., ON/OFF
sequencing) of the pulsed air mixing control system is site-specific, depending on the settleability
of the mixed liquor suspended solids and the geometry of the anaerobic/anoxic compartments.
For the SJ/SC WPCP, an air flow rate and timing sequence were established by trial and error that
maintained solids in suspension while keeping the dissolved oxygen concentration low enough
(0.2 mg/L or less) so as not to significantly hinder the anaerobic/anoxic process. The adequacy of
the mixing provided by the pulsed air system was verified by confirming equal concentrations of
solids on the bottom and at the surface of the anaerobic/anoxic compartments (at the end of the
air "ON" cycle). At the end of the "OFF" cycle, a bit of sludge settling occurs. At the end of the
"ON" cycle, it is important to ensure that sludge resuspension has occurred.
During implementation of the pulse air mixing control, engineers discovered that
providing simultaneous pulsed air for multiple tanks could lead to oscillation of the blower output.
A special programming routine was subsequently developed to avoid this control system
oscillation. The new routine sequences the tanks rather than simultaneously providing air to all
the tanks to re-suspend solids.
Evaluation of Energy Conservation Measures 6 September 2010
San Jose / Santa Clara (CA) WPCP Case Study
-------
Dissolved Air Floatation (DAF) Process Optimization
Optimization of the DAF process was achieved by reducing the energy used by the
pressurization pumps. This was made possible by utilizing proprietary algorithms developed by
Ekster and Associates that provided the means to optimize the DAF control systems.
Prior to optimization, each DAF tank was operating at a constant pressurized flow, which
was significantly higher than required. The algorithm allowed automatic adjustment of the
pressurized flow based on the number of DAF tanks in service and the incoming solids load to
maintain the same Air to Solids ratio (A/S) under all operating and influent conditions. The new
algorithm also provided a close approximation of equal solids loading throughout the day for each
DAF unit. The minimum A/S was determined by trial and error. The criterion utilized to establish
the minimum A/S was the equality of water and sludge concentrations before and after A/S
reduction. The current A/S stands at 0.005 and is one of the lowest ever reported in the
literature.
The control system algorithms for the in-plant pumping systems, pulsed air mixing system, and
DAF process were implemented and commissioned in 2008. Sub-metering of electrical power for
the DAF process was also implemented as part of the ECM project. Electrical sub-metering for the
in-plant pumping systems and BNR2 plant blowers were installed prior to the ECM project (with
their original design) as was the gas metering (for the combined mixture of landfill gas, digester
gas, and utility supplied natural gas) for the BNR1 plant internal combustion engine driven
blowers.
Tables 3a and 3b provide a comparison of the major water quality indicators associated
with the SJ/SC WPCP influent and effluent in 2007 prior to the implementation of improvements
and post ECM implementation performance.
Evaluation of Energy Conservation Measures 7 September 2010
San Jose / Santa Clara (CA) WPCP Case Study
-------
Parameter
BOD
TSS
NH3
Influent
Effluent
Monthly Permit Limit
Influent
Effluent
Monthly Permit Limit
Influent
Effluent
Monthly Permit Limit
2007
Daily Average
Concentration, mg/L
332
3.1
10
291
1.5
10
27.9
0.5
3
Nov. 2009 - Feb. 2010
Daily Average
Concentration, mg/L
363
3.7
10
293
1.5
10
31
0.6
3
Table 3b: Daily Maximum
Parameter
BOD
TSS
NH3
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
2007 Daily Maximum
Concentration, mg/L
438
5.0
20
534
3.5
20
43.8
1.4
8
Nov. 2009 - Feb. 2010
Daily Maximum
Concentration, mg/L
516
6.0
20
546
2.1
20
41.8
1.8
8
Table 3c provides comparison of DAF performance before and after optimization
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
Thickened Solids (%)
Underflow Total Suspended Solids (mg/L)
Before Optimization
After Optimization
Before Optimization
After Optimization
3.8
3.8
92
87
E CM Implementation Cost
Table 4 summarizes the cost associated with the implementation of the ECM projects.
Project
Liquid Pumping
Optimization
Pulse Aeration
DAF Process
Optimization
Capital Cost
$4,545
$62,822
$2,948
Implementation
Cost
$39,223 1
$118,770
$41,261
Total Cost for
All ECM
Total
Cost
$43,768
$181,592
$44,209
$269,569
1 Implementation cost included data collection, data verification, installation of power meters and software
costs.
Pump Station Optimization
Optimizing the pump stations led to energy reductions of between 17% and 23.5% (see
TableS).
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
September 2010
-------
Pump Station
Post Screening
Post Primary
Settling
Post Clarification
Before Optimization
(kW/million gal)
59.58
84.51
126.51
After Optimization
(kW/million gal)
46.25
64.62
104.88
Energy Use
Reduction
(kW/MG)
-13.33
-19.89
-21.63
%
Reduction
22%
23.5%
17.1%
BNR Process Improvements
Table 6 summarizes energy savings achieved by converting from continuous to pulsed
aeration in the BNR process.
BNR1
No. 1
No. 22
Annual Energy Consumption
Before
Optimization
3.1X10nBTU
6.2 X 10s kWh
After
Optimization
1.9X10nBTU
1.4 X 10s kWh
Energy Savings
Net Annual Savings
After Optimization
1.2X10nBTU
4.8 X 10s kWh
%
Reduction
38%
22.5%
Notes:
1. BNR = biological nutrient removal
2. Energy used only for mixed liquor channel aeration
DAF Process Optimization
Table 7 summarizes energy savings achieved through the DAF optimization ECM project.
Annual Energy Consumption
Before
Optimization
2,496,600 kWh/yr
After
Optimization
893,570 kWh/yr
Energy Savings
Net Annual Savings
After Optimization
1,603,030 kWh/yr
%
Reduction
64%
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
10
September 2010
-------
Table 8 summarizes the payback for the SJ/SC WPCP ECM projects.
Project
Liquid Pumping
Optimization
BNR Process
Improvements
DAF Process
Optimization
Total Cost
$43,768
$181,592
$44,209
Annual
Savings
(@$0.11/kWh)
$244,858
$176,339
$176,339
Annual
Savings
($l/Therm)
N/A
$581,275
N/A
Payback
Period
(Months)
2.1
2.9
3.0
PG&E reimbursed the plant $269,569 for these three ECM projects.
1. All ECMs were initially extensively tested on one unit before implementing the modification
for the entire system. This provided the staff with the confidence that the ECMs will not have
a negative effect on the performance of the treatment processes.
2. Measures are quickly reversible and adaptable to changing operational situations. One
example is the suspension of pulsed aeration for a few brief period to accommodate
operational corrective measures required to deal with foam observed from time to time on
the surface of aeration basins.
3. Rebates from electrical utilities provided additional incentives for prioritizing the
implementation of the ECMs.
In addition to energy saving resulting from this project, it is expected that the service life of the
pumps will increase as a result of operating the pumps closer to their best efficiency points (BEP).
Significant savings can be achieved with minimum capital investment by optimizing operating
procedures and process control set points. However, changes in operating protocols and/or
operating parameters require significant testing to ensure that these measures do not jeopardize
plant reliability and water quality.
Evaluation of Energy Conservation Measures
San Jose / Santa Clara (CA) WPCP Case Study
11
September 2010
-------
EPA would like to acknowledge the following individuals for the generous contributions to this
case study:
Bhavani Yerrapotu, Division Manager, Environmental Services Department, City of San Jose, CA
Medi Sinaki, Sanitary Engineer, Environmental Services Department, City of San Jose, CA
Steve Colby, Control System Specialist, Environmental Services Department, City of San Jose, CA
Issayas Lemma, Sanitary Engineer, Environmental Services Department, City of San Jose, CA
Rong Liu, Sanitary Engineer, Environmental Services Department, City of San Jose, CA
Medi Sinaki, Bhavani Yerrapotu, Steve Colby, Issayas Lemma Permit Safe, Energy Smart-Greening
Wastewater Treatment Plant Operations. Proceedings of 82nd WEFTEC, Conference and
Exposition, Orlando, 2009.
Alex Ekster Optimization of Pump Station Operation Saves Energy and
Reduces Carbon Footprint Proceedings of 82nd WEFTEC, Conference and Exposition, Orlando,
2009.
Issayas T. Lemma, Steve Colby, Tom Herrington Pulse Aeration of Secondary Aeration Tanks Holds
Energy Saving Potential without Compromising Effluent Quality Proceedings of 82nd WEFTEC,
Conference and Exposition, Orlando, 2009.
Utility Contact Information:
Dale Ihrke, Plant Manager / Bhavani Yerrapotu, Division Manager
SJ/SC WPCP
700 Los Esteros Rd.,
San Jose, CA 95134
Telephone: (408) 945-5300
email: Dale.Ihrke@sanjoseca.gov / Bhavani.Yerrapotu @sanjoseca.gov
Evaluation of Energy Conservation Measures 12 September 2010
San Jose / Santa Clara (CA) WPCP Case Study
-------
EVALUATION OF ENERGY CONSERVATION MEASURES FOR
WASTEWATER TREATMENT FACILITIES
CASE STUDY NO.9
Aeration System Improvements -DO Controlled Blowers and Fine Bubble Diffusers
Waco Metropolitan Area Regional Sewer System
Waco, Texas
Facility Size: 37.8 mgd design, 22.8 mgd average daily flow
Figure 1: Aerial View of the WMARSS WWTP
[Photo provided courtesy of WMARSS)
Facility/Process Description:
The Waco Metropolitan Area Regional Sewer System (WMARSS) treatment facility serves
approximately 175,000 people from the cities of Bellmead, Hewitt, Lacy-Lakeview, Robinson, Waco and
Woodway (Texas). In the early 1970's WMARSS was originally commissioned as a trickling filter plant
and was upgraded to a 37.8 mgd activated sludge plant in 1983-1985. In 1995, the plant was upgraded
to perform single stage nitrification. WMARSS facility influent data are presented in Table 1.
Evaluation of Energy Conservation Measures
WMARSS WWTP Case Study
September 2010
-------
Table 1: Profile of WMARSS Influent Data
WMARSS Influent Quality 2009
Parameter
Flow (mgd)
BOD (mg/L)
TSS (mg/L)
Ammonia-N (mg/L)
Average
22.8
251
300
31.5
Daily Maximum
608
2671
95.1
Peak
83.2
Figure 2 presents the process flow diagram for the WMARSS WWTP, a single stage nitrifying
activated sludge treatment plant.
Influent undergoes screening followed by primary clarification. Primary clarified effluent is
distributed to five aeration basins, typically operated in a plug flow mode (in which primary settled
wastewater and return activated sludge enter the head end of the aeration tanks and air is generally
distributed uniformly throughout the length of the aeration tank). During high influent flow conditions,
the aeration process is operated in a step feed mode (a modification of plug flow in which the primary
clarifier effluent is introduced at several points in the aeration tank and the secondary return activated
sludge (RAS) is introduced in the anoxic zone, resulting in a reduced MLSS loading entering the
secondary clarifier). The first 50 feet (ft) of each aeration basin is maintained as an anoxic zone which
receives RAS from the secondary clarifiers. Currently, RAS achieves oxygen savings in the aeration basins
(as oxygen is stripped from the nitrate in the RAS stream in the anoxic zone). In the future, the anoxic
zone and associated RAS will accommodate biological nutrient removal (phosphorus and nitrogen).
Each aeration basin measures 50 ft wide by 251 ft long and has a sidewater depth of 18 ft (total basin
volume = 8.45 million gallons). Seven Hoffman multi-stage centrifugal blowers (five 250 hp blowers at
6,000 standard cubic ft per minute (scfm) each and two 650 hp blowers at 12,500 scfm each) provide a
total of 55,000 scfm through a fine bubble diffuser system.
Aeration is followed by secondary clarification in four clarifiers. Variable portions of the
secondary clarifier effluent are pumped to sand filters. Unfiltered secondary clarifier effluent is blended
with filtered effluent and the combined effluent stream undergoes chlorination and de-chlorination
prior to reuse and/or discharge to the Brazos River.
Primary sludge undergoes two-stage thickening (gravity followed by rotary drum) prior to
anaerobic digestion. Secondary waste activated sludge (WAS) is thickened in the Rotary Drum Thickener
RDT) prior to digestion. The WAS is used as Mixed Liquor Suspended Solids (MLSS) seed for side stream
treatment. Supernatant from the rotary drum thickener is combined with gravity thickener supernatant
for sidestream treatment (existing trickling filters [and/or aeration currently under construction]
followed by a final solids clarifier). Filtrate from sludge dewatering may also undergo sidestream
treatment or be returned to the head of the plant. Sludge from the sidestream treatment final solids
clarifier is thickened (by gravity and/or by rotary drum) prior to anaerobic digestion. A portion of the
sidestream treatment final clarifier underflow is returned to the anoxic zone of the sidestream
treatment process.
Evaluation of Energy Conservation Measures
WMARSS WWTP Case Study
September 2010
-------
Sand Filt
rs Unit
Plant Influent
Aeration Influent
Final Clarifier Influent
Return Activated Sludge Flow
Waste Activated Sludge Flow
Primary Sludge flow
Gravity Thickened Sludge Flow
RDT Thickend Sludge Flow
Industrial Waste Septage
Solids Side Final Clarifier Under Flow
Solids Side Return Sludge
Gravity Thickener Supernatant
WAS Seed to Side Stream Treatment
Solids Side Final Clarifier Influent Flow
Digested Sludge Flow
Dewatered Sludge to Disposal
Side Stream Final Effluent
Dewatering Filtrate Flow
RDT Supernatant
Plant Final Effluent To Reuse
Plant Final Effluent River
Figure 2: WMARSS Process Flow Diagram
(graphic provided courtesy of WMARSS)
Evaluation of Energy Conservation Measures
WMARSS WWTP Case Study
September 2010
-------
Overflow from the sidestream treatment clarifier is returned to the head end of the plant. The
plant has four mesophillic anaerobic digesters that can be operated in series, parallel, complete mix or
as a combination of primary/secondary digesters. Industrial waste is received via tanker at the WMARSS
facility in the form of blood, sludge and grease (animal source) from local food processing
establishments (averaging 13,000 gallons per day). This industrial/commercial waste is treated with the
primary and secondary sludge in the anaerobic digesters. Digested sludge is dewatered using a belt
press or sent to surface disposal (sludge lagoons). Dewatered sludge is dried and pelletized (or
composted, in the future).
Description of Energy Conservation Measures (ECMs):
The City of Waco, Texas Utility Services Department implemented improvements to the aeration
system at their WMARSS treatment facility to address deficiencies in the plant's nitrification process.
Single-stage nitrification was not possible using the existing diffuser system because insufficient oxygen
was being supplied to the aeration process. The existing diffusers were being operated in excess of their
design air flow rate, producing coarse bubbles instead of fine bubbles, and the number of diffusers was
inadequate.
The aeration system improvements consisted of the following:
• Supplementing the existing Sanitaire fine bubble membrane and ceramic disc diffusers with
additional diffusers. The number of diffusers in each basin was increased from 2,800 to 3,500.
• Installing Danfoss dissolved oxygen (DO) probes in each of the aeration basins' three aeration
zones (mid-way in the first and second aeration zones and at the end of the third aeration zone).
• Implementing automatic blower and aeration system control through the plant's PLC system
using aeration basin DO readings. The plant's control system software provided the following
output based on aeration basin DO readings:
o ON/OFF control of blowers.
o Blower inlet valve throttling.
o Aeration system drop leg throttling.
ECM Commissioning Date:
The aeration basins' diffuser system was supplemented with additional diffusers in February
2003. Additionally, DO probes were installed in the aeration basins and the aeration control system was
programmed to utilize DO readings in the aeration basins to control the operation of the blower inlet
and basin drop leg throttling valves.
Description of ECM Project Drivers and Issues:
Implementation of the aeration system improvements was initiated to address problems with
completing the plant's nitrification cycle. Drivers for the project included requirements for increasing
the plant's capacity, improving effluent quality and to effect energy savings.
Evaluation of Energy Conservation Measures 4 September 2010
WMARSS WWTP Case Study
-------
Plant Influent and Effluent Quality
Tables 2a and 2b provide a comparison of the WMARSS facility performance prior to the
implementation of aeration system improvements (Y2002) and current (post ECM implementation)
performance.
Table 2a: Monthly Average
Parameter
BOD
TSS
NH3
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2002 Monthly Average
Concentration, mg/L
322.58
2.81
10
419.56
3.06
15
15.78
1.446
3
Y2009 Average
Concentration, mg/L
251
2.31
10
300
1.2
15
31.5
0.33
3
Table 2b: Daily Maximum
Parameter
BOD
TSS
NH3
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Influent
Effluent
Permit Limit
Y2002 Daily Maximum
Concentration, mg/L
644
7.8
25
1600
11.7
40
26.7
13.8
10
Y 2009 Daily Maximum
Concentration, mg/L
608
9.4
25
2671
5.5
40
95.5
4.96
10
Results
ECM Implementation Cost
Table 3 summarizes the implementation cost for the WMARSS aeration system ECM project:
Evaluation of Energy Conservation Measures
WMARSS WWTP Case Study
September 2010
-------
Table 3: ECM Implementation Cost
Cost Category
Capital Components
• Additional diffusers
• PLC automation
• DO instrumentation
• Air control valves
Total Capital Cost
Installation Costs1
• Aeration Improvements
• Aeration Improvements
Total Installation Costs (Est.)
Total Project Cost
Cost (in Y2002 $)
$239,200
$ 24,906
$ 18,420
$66,692
$349,218
$18,390
$30,100
$48,490
$ 397,708
Note 1 - ECM installation was performed by plant personnel so no
contractor installation costs were incurred.
Energy
Table 4 summarizes the WMARSS facility electrical energy consumption and costs prior to and following
the implementation of the aeration system improvements. The last column presents the electrical cost
savings per year at the facility.
Table 4: Electricity Use and Estimated Savings
Year
A
Total
Annual
Electricity
Use (kWh)
B
Annual Energy
Consumption
Reduction
(kWh)
c
Average
Daily
Flow (mgd)
D
Electricity Use per
Average Daily Flow
(kWh/mgd)
E= B/C
Average
Electricity
Rate
($/kWh)
F
Electricity
Cost
Savings ($)
^ ~~ \^ evaluation year
- B2002)*F
Prior to ECM Implementation
2002
14,076,530
26.4
532,431
$ 0.0430
Following ECM Implementation
2003
2004
2005
2006
2007
2008
11,624,105
11,006,112
9,201,249
7,969,924
7,851,481
8,949,861
2,452,425 (17%)
3,070,418 (22%)
4,875,281 (35%)
6,106,606 (43%)
6,225,049 (44%)
5,126,669 (36%)
24.3
28.8
24.6
21.7
27.6
22.9
477,996
382,366
373,701
367,563
284,400
390,765
$0.0537
$0.0650
$ 0.0689
$ 0.0897
$0.1150
$0.1187
$ 131,695.22
$ 199,577.17
$335,906.86
$ 547,762.56
$ 715,880.64
$608,535.61
Notes:
Column B - Data provided by WMARSS. Electricity use includes plant and sludge dryer combined. Sub metering is not conducted at WMARSS.
Column D - Data provided by WMARSS.
Column F - Rate data by WMARSS. If a rate change occurred during the year, a weighted average rate for the year was calculated based on
electricity consumption.
Evaluation of Energy Conservation Measures
WMARSS WWTP Case Study
September 2010
-------
Payback Analysis/Benefits
For this analysis, simple payback is determined by dividing the total project cost ($397,708 from
Table 3) by the electricity cost savings for each year following the project implementation. The electrical
energy costs savings provided by the aeration system improvements resulted in a project payback in the
first quarter (March) of the third year following commissioning (2005), a 2.4 year payback.
Conclusions
Factors Leading to Successful ECM Implementation/Operation
Facility staff was directly involved in identifying the treatment plant's operational problems and
the process equipment and operational modifications to address the plant's operational problems. The
staff was also involved in the installation of the aeration system improvements.
The aeration system modifications resulted in improved plant performance, reduction in energy
consumption, and reduction in direct operator involvement required to maintain blower and aeration
system performance. Plant personnel reported that this ownership stake in the project was a critical
factor in the successful implementation and the continued successful operation of treatment system.
Impact on Other Operating Costs Resulting from ECM Implementation
In addition to energy savings resulting from this project, the following benefits were also
realized.
Labor: The standard operating procedure before automating the aeration
process was to manually check the DO concentration in each of the
basins' zones on an hourly basis and adjust the drop leg valves and the
blower demand in response to the DO readings. The utility estimates
that automation of the aeration saves approximately three hours of
operator labor per day (1095 hours per year) at a savings of $21,900 per
year.
Chemicals: With the ammonia cycle stabilized (less nitrite / chlorine demand in the
effluent), chlorine demand has been reduced and stabilized.
Prior to the implementation of the aeration system modifications, a
daily maximum of approximately 6,000 pounds of chlorine was dosed
per day (under normal flow conditions of approximately 25 mgd
whenever the plant had high effluent nitrate level). Currently (under
average daily flow conditions of 22.5 mgd and complete nitrification),
the average chlorine dosage ranges between 800 and 1200 pounds per
day.
During the implementation of the aeration system ECM, the effluent
chlorination monitoring and control system was also upgraded. It is not
Evaluation of Energy Conservation Measures 7 September 2010
WMARSS WWTP Case Study
-------
possible to segregate the chlorine chemical consumption/cost
reductions attributed exclusively to the ECM project since both the
upgraded chlorination monitoring and control system and the ECM
were commissioned during the same period in 2003/2004.
Maintenance: With the savings in energy cost and operator labor provided by
automating the aeration process, WMARSS is able to maintain adequate
staffing according to industry standards.
Lessons Learned
The project and the operational issues that provided the drivers for the aeration system
improvements have impressed upon the WMARSS management and operations staff to maintain a
"mindset of continually improving and re-evaluating operating practices because over time small,
unnoticed system limitations add up to system failure." (Source: Personal communications from Mike
Jupe - Plant Superintendent WMARSS January 18, 2010).
Acknowledgements
EPA would like to acknowledge the following individuals for their generous contributions to this
case study:
Michael Jupe, Program Administrator and Plant Superintendent, Waco Metropolitan Area
Regional Sewer System.
Kristy Wolter, Program Manager/Field Operations, Waco Metropolitan Area Regional Sewer
System.
References and Bibliography
Christodoss, Daniel; Garrett, Ricky and Jupe, Michael; Activated Sludge Plant Field and Model Evaluation,
Texas WET, July 2007.
Evaluation of Energy Conservation Measures 8 September 2010
WMARSS WWTP Case Study
-------
Utility Contact Information:
MikeJupe
Program Administrator/ Plant Superintendent
Waco Metropolitan Area Regional Sewer System
1147 Treatment Plant Road
Waco, Texas 76702
Telephone: (254) 662-1501
email: MJupe@ci.waco.tx.us
Evaluation of Energy Conservation Measures 9 September 2010
WMARSS WWTP Case Study
-------
This page left intentionally blank.
Evaluation of Energy Conservation Measures 10 September 2010
WMARSS WWTP Case Study
-------
Appendix B
Web Resources
-------
B.I Introduction
As interest in energy conservation for wastewater treatment plants has grown, so has the
number of governmental, private, and non-profit organizations involved in evaluating and implementing
energy conservation measures (ECMs). Table B-l provides a description of and the web link to national
and regional energy efficiency resources for wastewater treatment plants. Information is organized
according to the name or the organization and its type (e.g., book, government resource, state, non-
profit). The web links are current as of February 9, 2010.
Evaluation of Energy Conservation Measures B-2 September 2010
-------
Table B-l. Summary of Literature Sources
Type
EPA
Resources
Manuals and
Guidance
Documents
(by
organizations
other than
EPA)
Name/ Organization
Ensuring a
Sustainable Future:
An Energy
Management
Guidebook for
Wastewater and
Water Utilities
(USEPA 2008)
Wastewater
Management Fact
Sheet: Energy
Conservation (2006)
Sustainable
Infrastructure Web
site
ENERGY STAR for
Wastewater Plants
and Drinking Water
Systems
Region 1 Energy and
Water/ Wastewater
Infrastructure Web
site
Region 9 Sustainable
Water Infrastructure
Web site
Energy Conservation
in Water and
Wastewater
Facilities, Manual of
Practice No. 32 (WEF
2009)
Energy Audit Manual
for Water/
Wastewater Facilities
(EPRI 1994)
Web link1
http://www.epa.gov/waterinfra
structure/pdfs/guidebook si
energymanagement.pdf
http://www.epa.gov/owm/mtb/
energvcon fasht final.pdf
http://water.epa.qov/infrastruc
ture/sustain/basicinformation.
cfm
http://www.enerqvstar.qov/ind
ex. cfm? c= wate r. wastewate r
drinkinq water
http://www.epa. qov/reqion1/e
co/enerqv/ew-
infrastructure.html
http://www.epa.gov/reqion09/
waterinfrastructure/
Available for purchase at
http://www.e-
wef.orq/timssnet/products/tnt
products. cfm?primary id=W
090037&Action=LONG&subs
vstem=ORD
http://www.cee1 .orq/ind/mot-
sys/ww/epri-audit.pdf
Description
Provides water and wastewater
utility managers with a step-by-
step method based on a Plan-
Do-Check-Act management
system approach to improve
energy efficiency at their
utilities.
Provides comprehensive
approach to energy
conservation along with case
studies.
Provides basic information on
energy required for
water/wastewater and multiple
links to EPA resources
including benchmarking,
management, full cost pricing,
and on-site energy generation.
Provides information on how a
WWTP can become an
ENERGY STAR partner, sign
up for the ENERGY STAR
Challenge, and benchmark its
energy use with Portfolio
Manager.
Similar to the EPA Sustainable
Infrastructure Web site with
regional examples.
Provides detailed discussion
and links for energy-efficient
equipment and operations.
Provides case studies for co-
generation and renewable
power.
Standard manual for the water
and wastewater industry. In
depth information including
theory and practical
information.
Includes step-by-step process
for conducting an audit, process
ECM ideas, and tips for
creating an energy
conservation program.
Evaluation of Energy Conservation Measures
B-3
September 2010
-------
Type
Name/ Organization
Web link
Description
NEMA Standards
Publication
Condensed MG-1:
Information Guide for
General Purpose
Industrial AC Small
and Medium Squirrel-
Cage Induction
Motors Standards
Available for purchase at
http://www.techstreet.com/
bin/detail?doc no=NEMA%7
CMG 1 2009&product id=l
680007
Provides information on
performance, safety, test,
construction and manufacture
of ac and dc motors and
generators. Helps readers in
proper selection and application
of motors and generators
DOE
Resources
Alternative
Waste water
Treatment: On-Site
Biotreatment
Wetlands at the
Fernald Preserve
Visitors Center
http://www.lm.doe.gov/Fern
aid/Documents.aspx
Case study of decentralized
wastewater treatment
(constructed wetlands).
Process Optimization
Saves Energy at
Metropolitan
Syracuse
Wastewater
Treatment Plant
http://www1 .eere.energy.gov/i
ndustry/bestpractices/pdfs/on
ondaga county.pdf
Case study of energy efficiency
upgrades to WWTP in
Syracuse, NY. Process
improvements included
retrofitting motors, changing
impellers, and optimizing
operations.
City of Milford Pump
Optimization Case
Study
http://www1 .eere.energy.gov/i
ndustry/bestpractices/pdfs/mil
ford.pdf
Case study in which a WWTP
changed out oversized pumps
at lift station and reduced
energy use by 15%.
Town of Turnbull,
Connecticut Case
Study
http://www1 .eere.energy.gov/i
ndustry/bestpractices/case st
udy sewage pump.html
Case study in which WWTP
replaced an oversized pump at
a lift station and changed
operating strategy to reduce
electricity consumption by
almost 44%
Best Practices
Management Case
Study in Fairfield, OH
http://www1 .eere.energy.gov/i
ndustry/bestpractices/pdfs/fair
f.pdf
Case study of WWTP that used
systems approach to implement
improvements identified by
energy audit. Installed power
monitoring device, installed fine
bubble diffusers, and used
MotorMaster+ software.
Best Practices:
Motors, Pumps, and
Fans
http://wwwl.eere.energy.go
v/industry/bestpractices/mot
ors.html
Web site with best practices
resources specific to motor
systems, including reports,
tools, and training information
Adjustable Speed
Pumping
Applications:
Industrial Technology
Program, Pumping
system Tip Sheet #
11
http://wwwl.eere.energy.go
v/industry/bestpractices/pdfs
/38947.pdf
Tip sheet that provides
overview information on
adjustable speed pumping
applications and
recommendations for predicting
performance at various
operating points along a system
curve
Evaluation of Energy Conservation Measures
B-4
September 2010
-------
Type
Name/ Organization
Web link
Description
Improving Motor and
Drive System
Performance: A
Source book for
Industry, second
editiion
http://wwwl.eere.energy.go
v/industry/bestpractices/pdfs
/motor.pdf
Reference document published
in 2008 that outlines
opportunities for motor and
drive system improvements.
Includes guidance on how to
find more information and
assistance.
Pumping System
Assessment Tool
(PSAT) User Manual.
http://wwwl.eere.energy.go
v/industry/bestpractices/pdfs
/psat_user_manual.pdf
Provides basic information
about the the Pumping System
Assessment Tool including data
entry, calculated results, and
various control button features.
Improving Pump
System Performance:
A Sourcebook for
Industry, second
edition
https://www1 .eere.energy.gov
/industry/bestpractices/pdfs/p
ump.pdf
Reference document published
in 2009 that outlines
opportunities for pump system
improvements. Includes
guidance on how to find more
information and assistance.
Nonprofits
American Council for
an Energy Efficient
Economy (ACEEE)
http://www.aceee.org/publicat
ions
Organization dedicated to
advancing energy efficiency as
a means of promoting
economic prosperity, energy
security, and environmental
protection. Created a roadmap
for water and energy efficiency
in 2004. Web site provides links
to GEE and NYSERDA.
Consortium for
Energy Efficiency
(GEE), National
Municipal Water and
Wastewater Facility
Initiative
http://www.cee1 .org/ind/mot-
sys/ww/ww.php3
Resource link has extensive
links to reports, case studies,
and other resources. Includes
newly published energy
efficiency RFP guidance.
Flex Your Power —
California's statewide
energy efficiency
marketing and
outreach campaign
http://www.fvpower.org/bpg/rn
odule.html?b=institutional&m
=Water Use
Best Practice Guide for Local
Governments includes
guidelines for wastewater
utilities. Includes step-by-step
plan and links to other
resources.
Electric Power
Research Institute
(EPRI)
http://my.epri.com/portal/serv
er.pt?
Non-profit group representing
electric utility industry.
Conducts research and publish
reports related to energy
efficiency for wastewater
utilities.
Evaluation of Energy Conservation Measures
B-5
September 2010
-------
Type
State
Programs
and Activities
Water
Research
Foundation
(WRF)2
Name/ Organization
Hydraulic Institute
Pump Systems
Matter Initiative
Massachusetts —
Energy Pilot for
Wastewater and
Water Treatment
Plants
on Energy
New York State
Energy Research and
Development
Authority
(NYSERDA) Focus
on Water and
Wastewater
California Energy
Commission
Water and
Wastewater Energy
Efficiency: A
Research Roadmap
(2004)
Web link1
www.PumpSystemsMatter.or
a
http://www.mass.qov/dep/wat
er/wastewater/eerewwu.htm
http://www.focusonenergy.co
m/Business/lndustrial-
Business/Wastewater.aspx
http://www.nyserda.org/Progr
ams/Environment/muniwater
wwt.asp
http://www.nypa.gov/press/20
09/09031 8. htm
http://www.energy.ca.gov/pro
cess/water/wastewater treat
ment.html
http://www.energy.ca.gov/200
4publications/CEC-500-2004-
901/CEC-500-2004-901 .PDF
Description
Goal is to provide tools and
trainings for optimizing pump
operation and improving energy
efficiency. Provides pump
system assessment guide and
downloadable tool.
Brings together state and
federal agencies and electric
and gas utilities to conduct
facility energy audits, assess
each plant for its renewable and
clean energy possibilities, and
offer support for the
implementation of these
energy-related projects.
Energy Advisors help water and
wastewater plants conduct
audits, develop an energy
management plant, and identify
ECMs.
NYSERDA provides assistance
to identify and install ECMs, as
well as training and case
studies. They have recently
finalized a Water and
Wastewater Energy
Management Best Practices
Handbook, available for
download from this web site.
Related press release from the
New York Power Authority.
Provides resources for reducing
energy use at wastewater and
water treatment plants.
Extensive list and links to
articles, fact sheets, reports,
and technical papers on energy
efficiency.
The roadmap identifies and
prioritizes research projects that
will advance emerging
technologies and best practices
to improve energy efficiency
and reliability for water and
wastewater utilities.
Evaluation of Energy Conservation Measures
B-6
September 2010
-------
Type
Name/ Organization
Web link
Description
Evaluation of
Dynamic Energy
Consumption of
Advanced Water and
Waste water
Treatment Systems
(2008)
Summary available at:
http://www.hdrinc.com/Assets
/documents/Publications/Wat
erscapes/summer2006/Evalu
atingEnergy.pdf
Full report available for
purchase or free for
subscribers at:
http://www.waterresearchfoun
dation.org/research/TopicsAn
dProiects/projectSnapshot.as
px?pn=3056
Presents energy data for
advanced water and
wastewater treatment systems.
Water
Environment
Research
Foundation
(WERF)3
Knowledge Area:
Operations
Optimization
http://www.werf.org/AM/Temp
late.cfm?Section=Operations
Optimization
Site with WERF products and
Web links to support optimizing
processes to improve
performance, reduce energy
costs and carbon footprint.
An Assessment Tool
for Managing Cost-
Effective Energy
Recovery from
Anaerobically
Digested Wastewater
Solids (LCAMER,
2006)
http://www.werf.org/AM/Custo
mSource/Downloads/uGetEx
ecutiveSummary.cfm?FILE=E
S-01-CTS-
18UR.pdf&ContentFilelD=114
02
Assessment tool that
incorporates site-specific
information such as energy
costs, regulatory conditions,
and wastewater plant capacity
to help determine the most
cost-effective alternative for
recovering digester gas energy.
An Economic
Framework for
Evaluating the
Benefits and Costs of
Biosolids
Management Options
(2007)
http://www.werf.org/AM/Custo
mSource/Downloads/uGetEx
ecutiveSummary.cfm?File=E
S-04-CTS-
2.pdf&ContentFilelD=9208
Framework that assists utilities
with benefit-cost analysis; helps
agencies select and justify
biosolids management; and
provides guidance, resources,
and case study illustrations.
Producing Class A
Biosolids with Low-
Cost, Low-
Technology
Treatment Processes
(2004)
http://www.werf.org/AM/Custo
mSource/Downloads/uGetEx
ecutiveSummary.cfm?FILE=E
S-95-REM-
2.pdf&ContentFilelD=9017
Describes low-tech treatment
processes for producing Class
A biosolids under a variety of
conditions. Also provides
guidance to further reduce
pathogens.
State of Science
Report: Energy and
Resource Recovery
from Sludge (2009).
http://www.werf.org/AM/Custo
mSource/Downloads/uGetEx
ecutiveSummary.cfm?FILE=E
Si
OWS03R07.pdf&ContentFilel
D=7538
Improving
Wastewater
Treatment Plant
Operations Efficiency
and Effectiveness
(1999)
Discusses international practice
for energy and resource
recovery from sludge. Explains
influence of market and
regulatory drivers on sludge
end-products.
http://www.werf.org/AM/Temp
late.cfm?Section=Research
Profile&Template=/CustomSo
urce/Research/PublicationPro
file.cfm&id=97-CTS-1
Includes more than 40 case
studies of approaches and
methods for improving plant
performance and productivity,
and reducing service costs.
Evaluation of Energy Conservation Measures
B-7
September 2010
-------
Type
Name/ Organization
Web link
Description
Sensing and Control
Systems: A Review
of Municipal and
Industrial
Experiences (2002)
http://www.werf.org/AM/Temp
late.cfm?Section=Research
Profile&Template=/CustomSo
urce/Research/PublicationPro
file.cfm&id=99-WWF-4
Provides guidelines on
automation of WWTPs.
Energy Efficiency in
Waste water
Treatment in North
America: A
Compendium of Best
Practices and Case
Studies of Novel
Approaches (2010)
http://www.werf.org/AM/Te
mplate.cfm?Section=Search&
Template=/CustomSource/Re
search/Publication Prof ile.cfm
&id=OWSO4R07e
Includes recommendations on
incremental improvements
through optimization of existing
operations and more
substantial improvements from
adoption of novel technologies.
Sustainable
Treatment: Best
Practices from the
Strass in Zillertal
Waste water
Treatment Plant
http://www.werf.org/AM/Te
mplate.cfm?Section=Search&
Template=/CustomSource/Re
search/Publication Prof ile.cfm
&id=OWSO4R07b
Report highlights one of the
best performing wastewater
treatment plants in Europe - a
facility that produces more
energy than it requires for
operations.
WERF Best Practices
for Sustainable
Wastewater
Treatment: Initial
Case Study
Incorporating
European Experience
and Evaluation Tool
Concept (2009)
http://www.werf.org/AM/Temp
late.cfm?Section=Search&Te
mplate=/CustomSource/Rese
arch/PublicationProfile.cfm&id
=OWS04R07a
Evaluates the European
experience with energy
reduction and best practices at
wastewater treatment plants.
Highlights Strass im Zillertal
WWTP, a municipal facility that
provides for both nitrogen and
phosphorus removal while
producing more electricity on an
annual basis than it consumes.
Sustainability 2008:
Green Practices for
the Water
Environment (put on
by WEF)
See Note 4
Sessions on energy
management and renewables.
WEFTEC 2002 -
2008
See Note 4
Multiple sessions on energy
management and optimization.
Conference
Proceedings
WEF Residuals and
Biosolids
Management
Conference 2002 -
2008
See Note 4
Sessions on sustainability.
WEF Utility
Management
Conference 2008
See Note 4
Session on advanced tools.
WEF Membrane
Technology
Conference
See Note 4
Sessions on energy and
optimization of membrane
systems.
WEF and American
Water Works
Association (AWWA)
Joint Management
Conference
Proceedings
See Note 4
Session on innovative energy
ideas.
Evaluation of Energy Conservation Measures
B-8
September 2010
-------
Type
Journals
Name/ Organization
WEF's Water
Environment and
Technology (WE&T)
WEF's Water
Environment
Research (WER)
ASCE Journal of
Environmental
Engineering
Water and
Waste water
International
Web link1
http://www.wef.org/Publicat
ions/page wet.aspx
http://www.wef.orq/Publicatio
ns/paqe detail. aspx?id=796
http://pubs.asce.orq/iournals/
environmental/
http://www.waterworld.com/in
dex/world-reqions.html
Description
WEF membership required to
access full articles.
Requires special subscription
from WEF.
ASCE membership required to
access full articles.
e-newsletter on international
water and wastewater issues.
Requires subscription.
Notes:
1. Web links are current as of February 8, 2010
2. Formerly the American Water Works Association Research Foundation (AwwaRF)
3. WERF reports available for purchase or through subscription.
4. WEF-sponsored conference proceedings can be accessed through this Web site:
http://www.inqentaconnect.com/content/wef/wefproc
Evaluation of Energy Conservation Measures
B-9
September 2010
-------
------- |