NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Energy Efficiency Strategies for 

Municipal Wastewater 

Treatment Facilities 

J. Daw and K. Hallett 

National Renewable Energy Laboratory

J. DeWolfe and I. Venner 

Malcolm Pirnie, the Water Division of ARCADIS

Technical Report

NREL/TP-7A30-53341

January 2012
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Energy Efficiency Strategies 

for Municipal Wastewater 

Treatment Facilities 

J. Daw and K. Hallett 

National Renewable Energy Laboratory

J. DeWolfe and I. Venner 

Malcolm Pirnie, the Water Division of ARCADIS

Prepared under Task No. IGST.1104

Technical Report

NREL/TP-7A30-53341

January 2012
NOTICE

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iii

Contacts

National Renewable Energy Laboratory 

Jennifer Daw, PE, CEM, LEED AP

Sustainability Project Manager

1617 Cole Boulevard 

Golden, CO 80401 

Phone: 303-275-4678 

E-mail: Jennifer.Daw@nrel.gov

Kathleen Hallett

Energy Information Analyst 

1617 Cole Boulevard 

Golden, CO 80401 

Phone: 303-275-3725 

E-mail: Kathleen.Hallett@nrel.gov

Malcolm Pirnie, the Water Division of ARCADIS

James DeWolfe, PE, BCEE, CWO

Principal Environmental Engineer 

1951 Pine Hall Road, Suite 125 

State College, PA 16801 

Phone: 814-867-1477 

Email: James.DeWolfe@arcadis-us.com

Ifetayo Venner, PE

Senior Environmental Engineer 

14025 Riveredge Drive, Suite 600 

Tampa, FL 33637 

Phone: 813-353-5751 

Email: Ifetayo.Venner@arcadis-us.com
iv

Acknowledgements 

The National Renewable Energy Laboratory (NREL) would like to acknowledge the 

contributions of the U.S. Department of Energy’s Technical Assistance Program, the Office of 

Resource Efficiency, the town of Crested Butte, and Mt. Crested Butte Water and Sanitation 

District in the funding of this effort and Malcolm Pirnie, the Water Division of ARCADIS and 

Gunnison County Electric Association for their expertise in performing the energy audit.
v 

List of Acronyms and Abbreviations

ASHRAE American Society for Heating, Refrigerating and Air-Conditioning 

Engineers 

ATAD Autothermal Thermophilic Aerobic Digestion

BOD Biological Oxygen Demand

DO dissolved oxygen 

EPA U.S. Environmental Protection Agency 

GCEA Gunnison County Electric Association 

HP horsepower 

I&I infiltration and inflow 

MGD million gallons per day 

NREL National Renewable Energy Laboratory 

O&M operations and maintenance 

OpenEI Open Energy Information Initiative 

SCADA supervisory control and data acquisition

TSS Total Suspended Solids 

UV ultraviolet 

VFD Variable Frequency Drive 

WWTP wastewater treatment plant
vi 

Executive Summary

Water and wastewater systems are significant energy consumers with an estimated 3%-4% of 

total U.S. electricity consumption used for the movement and treatment of water and wastewater 

[1,2]. Water-energy issues are of growing importance in the context of water shortages, higher 

energy and material costs, and a changing climate. In this economic environment, it is in the best 

interest for utilities to find efficiencies, both in water and energy use. Performing energy audits 

at water and wastewater treatment facilities is one way community energy managers can identify 

opportunities to save money, energy, and water. 

In this paper the importance of energy use in wastewater facilities is illustrated by a case study of 

a process energy audit performed for Crested Butte, Colorado’s wastewater treatment plant1. 

The energy audit identified opportunities for significant energy savings by looking at power 

intensive unit processes such as influent pumping, aeration, ultraviolet disinfection, and solids 

handling. This case study presents best practices that can be readily adopted by facility 

managers in their pursuit of energy and financial savings in water and wastewater treatment. 

This paper is intended to improve community energy managers’ understanding of the role that 

the water and wastewater sector plays in a community’s total energy consumption. The energy 

efficiency strategies described provide information on energy savings opportunities, which can 

be used as a basis for discussing energy management goals with water and wastewater treatment 

facility managers.

 

1 Wastewater Division of the Public Works Department: http://tinyurl.com/889an5h
vii 

Table of Contents

1 Introduction ......................................................................................................................................... 1

Energy Use in the Water and Wastewater Sector ....................................................................1

EPA Region 8 Partnership .......................................................................................................1

2 Case Study: Crested Butte ................................................................................................................ 2

Background ..............................................................................................................................2

Crested Butte’s WWTP ............................................................................................................3

Energy Audit ............................................................................................................................3

Collecting Data ........................................................................................................................4

Existing Process Performance ..................................................................................................5

Influent Pumping/Headworks ............................................................................................5

Aeration/Oxidation Ditch ...................................................................................................6

Clarification .......................................................................................................................6

Ultraviolet Disinfection .....................................................................................................6

Solids Handling ..................................................................................................................6

Plant Walkthrough ...................................................................................................................6

Primary Opportunities for Energy Savings ..............................................................................8

Influent Pumping/Headworks ............................................................................................8

Aeration/Oxidation Ditch ...................................................................................................8

Ultraviolet Disinfection .....................................................................................................9

Solids Handling ..................................................................................................................9

Reducing Influent Flow ...................................................................................................10

Community Support .........................................................................................................10

Next Steps for Crested Butte..................................................................................................11

3 Strategies To Consider.................................................................................................................... 11

Process Energy .......................................................................................................................11

Operational Controls ..............................................................................................................12

Repair and Replacement ........................................................................................................12

Biosolids ................................................................................................................................12

Infiltration, Inflow and Leaks ................................................................................................13

On-Site Renewable Energy ....................................................................................................13

Conservation ..........................................................................................................................13

4 Resources ......................................................................................................................................... 14

5 Conclusion ........................................................................................................................................ 14

6 References ........................................................................................................................................ 15
viii

List of Figures

Figure 1. Crested Butte, Colorado .................................................................................................. 2

Figure 2. Crested Butte WWTP process flow diagram ................................................................... 3

Figure 3. Energy audit levels .......................................................................................................... 4

Figure 4. Collecting UV system power draw data .......................................................................... 7

Figure 5. Measuring DO profile ...................................................................................................... 7

Figure 6. Mechanical aerator in oxidation ditch ............................................................................. 9

Figure 7. Typical WWTP energy consumers ................................................................................ 11

Figure 8 Quality versus energy ..................................................................................................... 12

List of Tables

Table 1. Crested Butte WWTP: Major Energy Consumers ............................................................ 5

Table 2. Energy Savings Recommendations ................................................................................ 10

Table 3. Energy Efficiency Strategies for Municipal WWTPs ..................................................... 13
1 

1 Introduction

Energy Use in the Water and Wastewater Sector

Water and wastewater systems are significant energy consumers. An estimated 3%-4% of U.S. 

electricity consumption is used for the movement and treatment of water and wastewater [1,2]. 

The exact cost of energy use can vary widely from one utility to the next, with estimates ranging 

from 2%–60% of total operating costs [3,4]. Energy represents a substantial cost to wastewater 

utilities, as it is typically required for all stages in the treatment process, from the collection of 

raw sewage to the discharge of treated effluent. Given that water and wastewater treatment 

plants are not primarily designed and operated with energy efficiency as a chief concern, these 

systems can be overlooked when communities fund energy improvement projects. 

However, substantial energy and financial savings can be uncovered through operational changes 

and capital improvements at water and wastewater utilities. 

Operators and managers of water and wastewater facilities have a wide range of priorities, of 

which energy consumption is just one [5]. Some of their primary duties include: 

• Complying with regulatory requirements to meet customer, public health, and ecological 

demands 

• Providing reliable service at reasonable and predictable rates 

• Balancing repair and replacement needs with long-term debt, equipment condition, 

ongoing operations and maintenance costs, and revenue 

• Optimizing operations and maintenance to reduce costs and ensure longevity of assets. 

Allocating time to conduct an energy audit and make the necessary physical and operational 

changes can produce substantial benefits. Energy audits help identify the greatest energyconsumers at a facility, reveal opportunities for operational improvements, and detect issues with 

aging and underperforming equipment. The results of an audit can help to improve energy 

efficiency, which represents an opportunity for municipalities to reduce operating costs as well 

as impacts on both the environment and the surrounding community. 

EPA Region 8 Partnership 

The U.S. Environmental Protection Agency (EPA) Region 8 office serves the Intermountain 

West: Colorado, Montana, North Dakota, South Dakota, Utah and Wyoming. In October 2010, 

EPA Region 8 initiated the EPA Region 8 Utilities Partnership Energy Management Initiative for 

Public Wastewater and Drinking Water Utilities program with a focus on helping municipal 

water and wastewater utilities reduce energy consumption, improve reliability and performance, 

and minimize environmental impacts. In this program, the Region 8 office partnered with 10 – 

15 community water and wastewater facilities to complete the following tasks: 

• Benchmark current and future energy use in the EPA Portfolio Manager tool [6] 

• Perform process energy audits 
2 

• Develop an Energy Management Plan using EPA’s Ensuring a Sustainable Future: An 

Energy Management Guidebook for Wastewater and Water Utilities2

• Commit to implementing energy efficiency improvements and sharing results with the 

EPA Region 8. 

To increase the breadth of this program and provide value to municipalities that did not 

participate, EPA Region 8 plans to create a set of case studies to share with other water and 

wastewater utilities across the Intermountain West that profile some of the participating utilities 

and illustrate the process, benefits and challenges of optimizing energy performance. 

Figure 1. Crested Butte, Colorado

Source: NREL/PIX 19943

2 Case Study: Crested Butte 

Background

In support of their participation in the program, the town of Crested Butte was required to 

perform a process energy audit of its wastewater treatment plant (WWTP). The energy audit 

focused on readily implementable opportunities for energy reduction through process 

modification and operational improvements. The audit considered optimization of existing 

processes to realize improved control, monitoring, and WWTP effluent quality. The audit also 

helped the town begin tracking and benchmarking its WWTP energy use. 

The Department of Energy’s National Renewable Energy Laboratory (NREL) partnered with the 

town of Crested Butte, Malcolm Pirnie, the Water Division of ARCADIS, the Office of Resource 

Efficiency, and Gunnison County Electric Association (GCEA) (who served as the assessment 

team) in performing the energy audit. This partnership created an opportunity for these 

organizations to support local capacity development, working to educate communities and 

water/wastewater utilities on how to analyze and achieve energy efficiency savings. The intent 

of this paper is to share energy efficiency strategies learned from the Crested Butte process 

energy audit with other communities in order to help them achieve their energy reduction and 

environmental goals. 

 

2 http://www.epa.gov/owm/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf
3 

Crested Butte’s WWTP

Crested Butte is a small town located on the Western Slope of Colorado and is a major tourist 

destination for outdoor sports. The WWTP, constructed in 1997, serves the town, which has a 

permanent population of 1,500 people. The WWTP treats wastewater from residential and 

commercial customers, with no major industrial discharges to the plant. The plant also accepts 

solids from the Mt. Crested Butte Water and Sanitation District.

The town has an oxidation ditch WWTP, with a permitted capacity of 0.6 million gallons per day 

(MGD) for a 30-day average daily flow. The plant consists of grit removal, influent pumping, 

aeration, clarification, ultraviolet (UV) disinfection, and solids handling processes. Treated 

effluent from the plant discharges to the Slate River. Sludge is thickened and dewatered on-site 

and hauled to a local landfill for disposal. A simplified process flow diagram for the plant is 

shown in Figure 2. 

Figure 2. Crested Butte WWTP process flow diagram 

Source: NREL

Energy Audit

As part of the town’s participation in the EPA program, an energy audit of the treatment process 

was required. While not included in this study, building energy audits, which evaluate lighting, 

heating, cooling, and ventilation systems, can also yield substantial financial and energy savings 

in treatment facilities. 

There are three levels of energy audits outlined by the American Society for Heating, 

Refrigerating and Air-Conditioning Engineers (ASHRAE). These audit levels differ with respect 

to level of complexity, depth of analyses, and the degree of detail the audit can provide. Audits 

range from Level 1 (a walkthrough) to Level 3 (computer modeling). 
4 

Figure 3. Energy audit levels

Source: NREL

For Crested Butte, a Level 1 audit was performed, which included a plant walkthrough focused 

on treatment process energy use. The Level 1 audit: 

• Evaluates energy consumption and efficiency through an on-site survey to identify 

maintenance and/or operational needs and deficient equipment 

• Uses energy consumption information to understand usage patterns and to develop an 

energy baseline 

• Estimates energy and cost savings with an emphasis on low or no-cost measures.

Collecting Data

The process energy audit was initiated by compiling data from drawings, operational records, 

utility bills, and equipment inventories to develop an understanding of plant energy usage 

patterns. The assessment team consulted drawings to look for any operational or energy issues 

that could be associated with the physical layout of the plant. For example, the drawings showed 

that the existing dissolved oxygen (DO) meter was located in the anoxic zone of the oxidation 

ditch. This configuration does not establish an ideal feedback for oxygen control or oxidation 

ditch performance. It is typically more effective to locate this measurement device where DO 

levels are greater than zero, such as near the effluent of the ditch. 

Operational records and parameters such as Biological Oxygen Demand (BOD) and Total 

Suspended Solids (TSS) were used to distinguish patterns in raw water quality and WWTP 

performance. Plant operational data were used to establish three “operating seasons” with 

distinct raw water conditions. These seasons reflect changes in temporary population and 

infiltration experienced in the collection system throughout the year. The conditions associated 

with the three seasons are summarized below: 

• Season 1 (October – March): Low flow, low load (BOD, TSS on a pound per day basis), 

and low wastewater temperature

• Season 2 (April – June): High flow, average load, and low wastewater temperature

• Season 3 (July – September): Average flow, high load, and higher wastewater 

temperature.

Energy Audit Levels [7]

Level 1: Walkthrough assessment

Level 2: Energy survey & analysis

Level 3: Detailed analysis/ modeling
5 

The assessment team reviewed equipment inventories to determine the age and horsepower of 

plant equipment and to identify major energy consumers within the facility. An abbreviated list 

of major energy consumers in the town’s WWTP, along with their typical operations and 

controls, are summarized in Table 1. This information was used to focus audit efforts on major 

energy consuming processes within the plant to maximize energy savings opportunities. 

Table 1. Crested Butte WWTP: Major Energy Consumers

Existing Process Performance 

Each process was discussed in detail with plant operations staff to understand performance 

trends and concerns. General observations on the WWTP’s process performance and operational

strategies are described in the following paragraphs.

Influent Pumping/Headworks

The influent system consists of three pumps: 

• one 4.7 horsepower (HP) pump (Pump No. 1) 

• two 17.5 HP pumps (Pumps No. 2 and No. 3). 

Pump No. 2 runs continuously based on level detection in the wet well. All pumps have

Variable Frequency Drives (VFDs).

Equipment Quantity Horsepower Operations Controls

Mechanical 

Aerator 

1 75 Continuous Variable 

Frequency Drive

(VFD), manual 

adjustment

Centrifuge 1 40 10-20 hrs/week VFD, fixed speed

Influent Pump 

(No. 1)

1 4.7 Continuous VFD, speed based 

on flow

Influent Pumps 

(No. 2 & 3)

2 17.5 Pump No. 2 

continuous

Pump No. 3 backup

VFD, speed based 

on flow

VFD, speed based 

on flow

Blowers 3 15 Intermittent Fixed speed

Mixers 3 4 Continuous Fixed speed

UV System 2 banks 7.3 (kW) Continuous Fixed, 2 banks
6 

Aeration/Oxidation Ditch

The town’s WWTP has one oxidation ditch that provides aerobic removal of BOD and ammonia. 

There is an anoxic portion of the ditch that provides denitrification, recovers alkalinity, and 

reduces oxygen demand. The ditch has one 75 HP aerator running on a VFD that is operated 

based on manual adjustment from a daily DO concentration reading. Typically, energy savings 

from VFDs come from adjustments that are made automatically to adapt to system conditions, 

not manual adjustments. The ditch also has two continuously operated mixers in the anoxic 

zone. The existing DO meter located in the anoxic zone is not operational. 

Clarification

The WWTP has two clarifiers, one that operates continuously and a supplemental clarifier for 

high flow events. 

Ultraviolet Disinfection

The UV system was designed for a plant flow rate of 1.3 MGD (double the permitted capacity of 

the facility). The system currently operates with both banks on-line. Plant staff change UV 

system lamps once a year for preventative maintenance. 

Since 2008, the average effluent fecal coliform concentration has been 8.3 counts/100 milliliters

(mL) with a 7-day average of 214.3 counts/100 mL. The permitted effluent Escherichia Coli (a 

part of the group fecal coliform) concentration is 1372 counts/100 mL (30-day average) and 

2,744 counts/100 mL (7-day average). The current operational approach results in effluent fecal 

coliform levels that are significantly below permit requirements. 

Solids Handling

The WWTP has an Autothermal Thermophilic Aerobic Digestion (ATAD) system, which is not 

operational due to odor problems. Therefore, sludge is currently thickened in the raw sludge 

storage tank and transferred to the thickened sludge storage tank for holding. Due to existing 

plant piping configurations, sludge must be pumped from the thickened sludge storage tank to 

the ATAD holding tank to reach the centrifuge for dewatering. Although this allows for 

additional storage, and therefore potentially less frequent trips to the landfill, it also requires that 

the 15 HP blower associated with the ATAD storage tank remain operational. 

The 40 HP centrifuge is controlled by VFD, but typically runs at a constant speed. The 

centrifuge fills a 20 cubic yard dumpster once a week. Centrate from the centrifuge is piped to 

the oxidation ditch, which may affect performance of the oxidation process. 

Plant Walkthrough

Using this operational insight, the assessment team visited the WWTP to perform a Level 1 plant 

walkthrough. This effort consisted of visual inspections to identify operational or maintenance 

issues and the collection of energy data from major plant equipment. These data will be used by 

the town to develop estimated cost savings associated with operations and maintenance (O&M) 

and to prioritize capital improvements to the facility. 

GCEA assisted the assessment team during the audit by measuring actual power draw for major 

equipment, including sludge transfer pumps and blowers, which were rotated into operation for 

15-minute increments to record actual power use. Using a consistent time interval to measure 
7 

power draw allows sufficient time for power consumption associated with equipment start-up to 

level out. These data will be considered by the town to help make prioritizations for 

improvement. 

Figure 4. Collecting UV system power draw data

Source: NREL/PIX 19941

During the audit, DO concentrations were measured in the oxidation ditch to determine aeration 

effectiveness. These concentrations created a DO profile that was used to better understand plant 

operations. 

Figure 5. Measuring DO profile

Source: NREL/PIX 19942
8 

A BioWin model3

 was developed for the plant using influent characteristics, temperature, 

historical DO concentrations, typical aerator speeds, and the measured DO profile. Using this 

process model, the assessment team determined that the existing aerator, which is approximately 

15 years old, had poor transfer efficiency relative to newer aerators – meaning more energy is 

used to drive the aerator than would be expected for the resulting DO levels. 

Primary Opportunities for Energy Savings

Based on plant operational information and data collected during the audit, the assessment team 

developed energy savings recommendations for the WWTP. 

Influent Pumping/Headworks

Flow data provided for the WWTP indicates that infiltration and inflow (I&I) is problematic 

during Season 2 (April – June). To mitigate these issues, it is helpful to identify critical I&I 

areas in the collection system caused by leaks and breaks. This information will help to 

prioritize efforts to repair or replace system piping. 

Another best practice for Crested Butte’s WWTP is to tailor the operational strategy for the 

headworks to meet the three distinct seasons mentioned above. Using smaller horsepower 

equipment, such as Pump No. 1, to the extent possible, can reduce ongoing energy consumption. 

Based on typical daily flow patterns, Pump No. 1 could address nightly and mid-day low flow 

periods in Season 1 (October – March) and nightly low flow periods in Season 3 (July – 

September). As Pump No. 1 ages, the town may consider replacing it with a slightly higher 

capacity pump controlled by VFD to address wet well fluctuations. This increased capacity and 

improved controls would extend the pump’s operations during lower flow periods and minimize 

usage of the higher horsepower pumps. 

Aeration/Oxidation Ditch 

The DO levels measured in the oxidation ditch, in concert with other operational data, indicated 

that the aerator was not performing efficiently. Given that this is the largest horsepower motor at 

the WWTP, and that the aerator is nearing the end of its useful life, the assessment team 

recommends replacing it with a more energy-efficient model. The WWTP may also consider 

installing a new DO meter and/or ammonia sensor near the ditch outfall to provide more useful 

feedback on ditch performance. Connecting this meter to the plant supervisory control and data 

acquisition (SCADA) system will allow for continuous monitoring and control of DO levels. 

Additional energy savings can be achieved if these DO readings are used to automatically control 

the speed of the aerator. As a best practice, the mixers are recommended to only be used when 

the aerator is not operating, which will further reduce the energy use of this process.

 

3 BioWin is a Microsoft Windows-based simulator used in the analysis and design of wastewater treatment plants. 

http://www.envirosim.com/products/bw32/bw32intro.php
9 

Figure 6. Mechanical aerator in oxidation ditch

Source: NREL/PIX 19944

Ultraviolet Disinfection

Current operations of the UV system are consistent with the ultimate design flow rate, 1.3 MGD. 

With a current maximum operating flow rate of 0.6 MGD (less than half of the design flow rate 

of the UV system), the WWTP is surpassing permit requirements. Accordingly, the assessment 

team recommends that the WWTP operate only one bank of the UV system instead of both 

banks. Since the system was designed to treat significantly more wastewater than the WWTP 

currently receives, the facility could also work with the manufacturer to potentially modify the 

system to save energy by removing bulbs and retrofitting or de-energizing some of the ballasts. 

Connecting the UV system to SCADA would also improve control of performance. 

The WWTP may also consider replacing UV system lamps less frequently – the manufacturer 

recommends that bulbs be replaced after 13,500 hours of operation or every 1.5 years. Current 

operational practices are to replace bulbs as part of scheduled annual maintenance, regardless of 

running hours. Increasing the bulb replacement interval will save material costs and waste 

associated with operation of the plant. 

Solids Handling

The current solids handling process is operating inefficiently due to the use of existing ATAD 

system piping to reach the centrifuge for dewatering. When the ATAD system becomes 

operational again, this inefficiency will improve. However, the WWTP may also consider 

making piping retrofits to allow sludge to move directly from the thickened sludge tank to the 

centrifuge, bypassing the ATAD system. This change would eliminate transfer pumping within 

the solids handling system. 

One of the principal products of a WWTP is sewage sludge or biosolids [8]. Until two or three 

decades ago, the typical practice for WWTPs in Region 8 was to dispose of biosolids via landfill 

or incineration. These days, however, more facilities put biosolids to beneficial reuse and 85% of 

the biosolids generated in Region 8 are now recycled [9]. Most commonly, biosolids are used as 

a soil amendment to fertilize agricultural land or to restore soils on reclaimed land.

Crested Butte’s WWTP may also want to consider studying the energy requirements that are 

needed to treat its biosolids in order to divert them from the landfill for beneficial uses such as 

fertilizer for agriculture. While more energy is required to treat solids to a Class A or B 

standard4, it could also reduce vehicle miles to haul the material to the landfill, alleviate some of 

 

4 EPA Sewage Sludge (Biosolids): http://water.epa.gov/polwaste/wastewater/treatment/biosolids/genqa.cfm
10 

the long-term environmental burden of landfill disposal, and reduce greenhouse gas emissions 

associated with landfilled sludge. 

Reducing Influent Flow

Pinpointing areas in the collection system with I&I problems can help the WWTP to focus repair 

and replacement efforts. Infiltration of groundwater can be a major contributor to the WWTP 

influent flow. Regular cleaning, inspection, and slip lining of collection system piping can 

greatly mitigate infiltration and reduce the quantity of wastewater being treated.

Community Support

An active community-wide conservation program is another essential factor in reducing WWTP 

plant inflow. Working with the community to promote conservation awareness and to take 

actions such as installing water efficient fixtures, can significantly reduce flows at the WWTP 

and save energy. 

Recommendations and estimated energy and annual financial savings are shown in Table 2. 

These recommendations have been divided into short-term opportunities, which are lower cost 

and more readily implementable, and long-term opportunities, which would require more 

planning and capital expenditure. As presented in the table below, the aeration process offers the 

largest opportunities for energy and financial savings for the town of Crested Butte. 

Table 2. Energy Savings Recommendations

Process Recommendations Savings

(kWh - % energy - $/year)

Influent 

Pumping/Headworks

Use Pump No.1 during low flow (ST)

Conduct I&I study (LT)

Replace Pump No.1 (LT)

4,300 - 10% - $150

14,000 - 35% - $550 

8,700 - 20% - $350 

Aeration/Oxidation 

Ditch

Turn mixers off when aerator operates (ST)

Replace DO meter (ST)

Connect new DO meter to SCADA/

Replace aerator (LT)

45,900 - 90% - $1,750

19,800 - 10% - $750

123,000 - 40% - $4,700

UV Disinfection Remove one UV bank from service/ 

Determine if bulbs can be removed (ST)

32,000 - 50% - $1,200

Solids Handling Retrofit piping to feed sludge directly from 

thickened sludge tank to centrifuge (LT)

23,500 100% - $1,000

ST = short-term, LT- long-term
11 

Next Steps for Crested Butte

As a next step, the town will further quantify energy savings associated with the recommended 

improvements and begin work on their Energy Management Plan. The Energy Management 

Plan will establish the objectives and targets to be used to measure the town’s progress in energy 

reduction and will guide the town’s capital improvement efforts as well as plant O&M activities. 

Further information on how this information will be used can be found in the EPA’s Guidebook 

[10]. 

Crested Butte’s WWTP will also use its energy data to benchmark operational performance 

against other WWTPs, with the EPA Portfolio Manager. Portfolio Manager is a tool that can 

help the town identify further opportunities for performance improvement and prioritize 

investments.

3 Strategies To Consider

The Crested Butte case study is an excellent demonstration of how conducting an energy audit 

can improve a facility or community energy manager’s understanding of energy savings 

opportunities at water and wastewater facilities. The following sections provide a brief overview 

of several general energy savings strategies. Facility and community energy managers alike may 

want to consider how these energy savings strategies (summarized in Table 3) could be adopted 

at their community’s water and wastewater treatment facilities. Operators or managers who are 

ready to develop and implement a comprehensive energy management plan, and readers who are 

interested in step-by-step guidance, can get started with EPA’s Ensuring a Sustainable Future: 

An Energy Management Guidebook for Wastewater and Water Utilities [10]. 

Process Energy

When conducting an energy audit, focus efforts on the biggest energy consumers at the facility. 

This can be determined by reviewing drawings, nameplate data, or by measuring power draw of 

equipment. The aeration process is the largest energy consumer for most WWTPs as 

demonstrated by the typical WWTP energy usage patterns in Figure 7 [11]. 

Figure 7. Typical WWTP energy consumers

Source: Malcolm Pirnie, the Water Division of ARCADIS
12 

Quality

Energy

Operational Controls

Running a WWTP is not a “one size fits all” operation. Regularly evaluating influent and 

effluent trends can help utilities to tailor operational strategies accordingly. These parameters 

may vary by season, time of day, and/or have other unique characteristics. System controls that 

use SCADA feedback and VFDs can be used to optimize effluent quality and energy 

consumption. This balancing act is a continuous process that facility managers must consider, 

knowing that higher effluent quality is often at the expense of increased energy use. Achieving 

an optimal balance between quality and energy is the ultimate goal. 

Figure 8. Quality versus energy

Source: NREL

Repair and Replacement

As part of capital planning efforts, a best practice for facilities is to regularly evaluate the 

condition, performance and remaining useful life of process equipment. Aging equipment is 

more inefficient, can be costly to repair, and typically requires more energy than newer models. 

When doing an energy audit, equipment age and operational efficiency are major considerations. 

Evaluating preventative maintenance practices also helps to ensure that equipment is receiving 

appropriate maintenance for the level of use [12]. 

Biosolids

There are significant environmental and financial tradeoffs between providing higher quality 

biosolids and the subsequent energy demands. When evaluating biosolids treatment and disposal 

options, the following factors are important for facilities to consider [13]:

• Transportation – distance from the WWTP to the landfill affects cost to haul biosolids for 

disposal 

• Additional costs – tipping fees and additional treatment for land application may incur 

additional costs for biosolids 

• Revenue – WWTPs may receive payment for their biosolids as a soil amendment 

• Carbon emissions – landfilling of biosolids can result in greater emissions than land 

application

• Sustainability – using biosolids reduces demand for landfills and synthetic fertilizers, and 

can help the reclamation and re-vegetation process for brownfield sites.
13 

Infiltration, Inflow and Leaks

The wastewater collection system is another area of opportunity for utilities. A considerable 

amount of energy is wasted treating groundwater that infiltrates systems through pipes that are 

broken or out of alignment. Similarly, breaks and leaks in the collection system increase the 

energy required to pump sewage to the treatment plant. Focusing efforts on identifying areas 

with I&I, breaks, and leaks can enable utilities to direct repair and replacement efforts to areas 

that will provide greater energy and financial savings. 

On-Site Renewable Energy 

A best practice for all communities is to look for opportunities to incorporate on-site renewable 

energy at their facilities. After energy efficiency, renewable energy is another effective way to

save money by reducing energy purchases. All renewable resources available within the 

community, including wind, solar, water, and wastes generated on-site, may be considered as 

potential energy sources. These renewable systems are selected and installed to maximize 

energy production [14]. WWTPs with anaerobic digestion provide a unique opportunity to 

create on-site heat and power, by capturing biogas emissions as fuel for on-site energy 

generation [15]. 

Conservation

Effective outreach within the community can yield substantial reductions in water use and 

wastewater generation. Programs can be implemented that incentivize community members, 

businesses, and/or industries to reduce their water usage. By providing low-flow fixtures at a 

discounted fee, conducting water audits, and/or using inverted block rate structures, utilities can 

substantially reduce the amount of effluent to be treated and dramatically lower energy use 

within the community. Creating behavioral change through public education programs is 

another essential element in promoting conservation. As allowed by local water rights, 

maximizing the use of “fit for purpose” or reuse water may be considered as another 

conservation strategy. 

Table 3, below, summarizes the strategies that may be adopted by municipal wastewater 

treatment facilities to improve energy efficiency.

Table 3. Energy Efficiency Strategies for Municipal WWTPs

Focus Efforts for Energy Savings

 Process Energy Focus on biggest energy consumers at WWTP

 Operational Controls Tailor operations to meet seasonal and diurnal changes

 Quality vs. Energy Balance water quality goals with energy needs

 Repair and Replacement Consider equipment life and energy usage to guide repair and 

replacement

 Biosolids Consider tradeoffs between treatment energy and improved biosolids 

quality

 Infiltration/Inflow Address I&I to reduce treatment energy

 Leaks and Breaks Address leaks and breaks to reduce pumping energy

 On-Site Renewable

Energy

Consider opportunities for on-site generation to reduce energy 

purchases

 Conservation Educate the community: Less water reduces WWTP loads and energy 

needs
14 

4 Resources 

NREL provides access to hundreds of entries with helpful tools, as part of the Open Energy 

Information Initiative (OpenEI). OpenEI is a wiki that allows users to enter information directly

into its database, in order to share resources on renewable energy and energy efficiency: 

http://en.openei.org/wiki/Main_Page. 

NREL provides limited technical assistance through various federal programs. Under these 

programs, agencies may apply to receive technical assistance from NREL for understanding and 

deploying energy efficiency and renewable energy technologies: 

www.nrel.gov/applying_technologies/state_local_activities/technical_assistance.html. 

5 Conclusion

The Crested Butte case study demonstrates the importance of energy audits in providing 

community energy managers with the ability to recognize and implement energy saving 

opportunities at their facilities. Working to improve the understanding of energy patterns and 

efficiency opportunities is a best practice that all communities can adopt. By tracking energy 

usage, benchmarking, and making operational improvements, all communities can begin their 

efforts to reduce energy use and realize financial savings.
15 

6 References 

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Electricity Consumption for the Water Supply & Treatment–The Next Half Century. 

Topical Report1006787. Palo Alto, CA: EPRI, March 2002. 

2. Galbraith, Kate. “How Energy Drains Water Supplies.” New York Times, September 18, 

2011. Accessed September 22, 2011. 

http://www.nytimes.com/2011/09/19/business/global/19iht-green19.html?_r=1

3. Carlson, S.; Walburger, A. Energy Index Development for Benchmarking Water Utilities 

and Wastewater Utilities. Denver, CO: AWWA Research Foundation, 2007. 

4. Elliott, T.; Zeier, B., Xagoraraki, I.; Harrington, G. W. Energy Use at Wisconsin’s 

Drinking Water Facilities. Report 222-1. Madison, WI: Energy Center of Wisconsin, July 

2003. 

5. Utility Advisory Group. Effective Utility Management: A Primer for Water and 

Wastewater Utilities. Utility Advisory Group, June 2008. 

6. ENERGY STAR®.

 Portfolio Manager Overview. Accessed October 27, 2011. 

http://www.energystar.gov/index.cfm?c=evaluate_performance.bus_portfoliomanager

7. American Society for Heating, Refrigerating and Air-Conditioning Engineers 

(ASHRAE). “Energy Use and Management,” Chapter 36 in ASHRAE Handbook - HVAC 

Applications. (Atlanta: 2011).

8. U.S. Environmental Protection Agency (EPA). Biosolids: Targeted National Sewage 

Sludge Survey Report – Overview. EPA 822-R-08-014. January 2009. 

9. U.S. Environmental Protection Agency (EPA). Biosolids. Accessed September 22, 2011. 

http://www.epa.gov/region8/water/biosolids

10. U.S. Environmental Protection Agency (EPA) and Global Environment and Technology 

Foundation. Ensuring a Sustainable Future: An Energy Management Guidebook for 

Wastewater and Water Utilities. January 2008. 

11. Malcolm Pirnie, the Water Division of ARCADIS (2011). “Typical Energy Usage 

Patterns in U.S. Wastewater Treatment Plants.”

12. National Asset Management Strategy Group. International Infrastructure Management 

Manual, 2011. 

13. Raucher, R.S.; Garver, D.; Hallett, K.; Henderson, J.; Wagner, C. An Economic 

Framework for Evaluating the Benefits and Costs of Biosolids Management Options. 

Alexandria, VA: Water Environment Research Foundation, 2007. 
16 

14. Federal Energy Management Program, Renewable Energy Resources and Technologies. 

Accessed December 2, 2011. 

http://www1.eere.energy.gov/femp/technologies/renewable_technologies.html

15. U.S. Environmental Protection Agency (EPA). Combined Heat and Power Partnership. 

Accessed December 2, 2011. http://www.epa.gov/chp/markets/wastewater.html