One Year of Energy Net-Zero Via
Energy Efficiency and FOG Codigestion
at the Gresham, OR WWTP
Jeff Maag, Project Manager, Wastewater Services Division, City of Gresham
Jeff McCormick, Project Manager, Carollo Engineers
City of Gresham WWTP
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Gresham’s Wastewater Treatment Plant
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114,000 service population
 13 mgd annual average flow
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Secondary, Activated Sludge, Anaerobic Digestion
Discharge to Columbia River
Contract Operator: 17 FTE in Operations & Maintenance
(Veolia Water)
3 FTE in WWTP and PS Engineering (City of Gresham)
One of a handful of Energy Net-Zero WWTP’s in the U.S.
Energy Net Zero: producing more energy than consumed
City of Gresham WWTP
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New era of energy production began in
2005 with modern 400 kw Cogen No. 1
 Two 1 million gallon Anaerobic Digesters at WWTP
 Digesters treat solids in absence of air – biogas is
produced (65% methane, 35% CO2)
 Cogen burns biogas to produce electricity and hot water
CAT Model G3508LE
City of Gresham WWTP
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Cogen 1 Has Been Very Successful
 93% Runtime since 2005 (off about 48 hours per month)
 Produces power and heats buildings with jacket water heat
 55% of WWTP Power needs
 $250,000 annual avoided electrical costs
 2.1 cents per kwh operation/maintenance expenses
 3.5 year payback
City of Gresham WWTP
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Several major developments in 2008 and
2009 on our path to energy net-zero
 ACWA / Energy Trust “Energy Independence Project” studied 2
plants in Oregon, including the Gresham WWTP
 Gresham City Council passed a Sustainability Policy
 Kicked off feasibility study of FOG Receiving Station and Cogen
Expansion
 Solar Array became operational
City of Gresham WWTP
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Energy Independence Project
A Project for
Oregon Association of Clean Water Agencies
and
The Energy Trust of Oregon
Prepared by
Kennedy/Jenks Consultants
June 2008
General Recommendations
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Do Energy Efficiency First!
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Most cost-effective option
An energy audit can help identify cost-effective
Energy Efficiency Measures
Install identified EEMs and seek funding $
Resource Options
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Cogen engines are the most cost-effective for
producing renewable energy
Investigate a FOG Receiving program to enhance
digester biogas production and energy possibilities
Energy Independence Project
Gresham’s Sustainability Policy
Key Goals (2009)
 1) 80% Reduction in City Greenhouse Gas Emissions by
2050
 2) 100% Renewable Energy by 2030
 3) Zero Waste in City Operations by 2020
 4) Ongoing Protection of Natural Resources (including water
quality and availability, and habitat)
 5) Toxin Reduction and Eventual Elimination
WWTP had large potential to contribute towards goal 1 and 2.
City of Gresham WWTP
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FOG Feasibility
Study Highlights
 $40,000 Grant from State Economic Development Dept.
 Adding FOG Receiving Facilities is Economically Viable
 There is a market for this service in our area
 An additional 400 kw Cogenerator is economically viable
 FOG Tipping Fee of at least 3 cents per gallon required
 Need 7,000 to 11,000 gpd of FOG
 Estimated cost of $3.7 million
 Leverage $1.5 million in potential grants
 Simple payback of 7 years
City of Gresham WWTP
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420 kw Solar Array installed 2009
 Installation Dec. 2009
 420 kW peak capacity
 Provides 7% of WWTP power
 1+ acre ground-mounted system
 Power Purchase Agreement with
SunEdison in July 2009
 PGE net metering agreement
 No capital cost to City
 kwh charge 2/3 PGE rate
 Fixed annual escalation of 3%
City of Gresham WWTP
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2010 Energy Management Team
 Set Goal for Energy Net-Zero WWTP by 2015
 Selected Energy Team Members (Team Leader, Ops
Manager, engineering, Maintenance Manager)
 Meet Monthly for 1 hour and talk only energy
 Develop Energy Management Plan (keep it simple)
 Update and discuss Monthly energy production and
consumption numbers every month
 Select, prioritize and evaluate projects
 Stay on track!
 Keep running agenda in Energy Management Plan
City of Gresham WWTP
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2011 Master Plan included continued study of “Energy
Independence”
FOG Receiving / Cogen
Expansion and “Energy
Independence” was included
in our master planning
process
City of Gresham WWTP
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Energy Conservation Project, 2012 - 16%
Energy study funded by Energy Trust
New high efficiency
Neuros blowers and
aeration
diffusers replaced
aging equipment
Linear Motion Mixer
Aging digester gas
mixing was replaced
by Linear Motion
Mixers
City of Gresham WWTP
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Replace aging, out
of date blowers with
modern efficient
blowers
 Replace 2 Hoffman mutistage blowers (100 hp
each)
 Install 2 Neuros Turbo blowers (100 hp each)
 Operating curves are much more efficient
 50% variable speed turndown
 Air bearings
City of Gresham WWTP
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Inefficient Sock Diffusers
High Efficiency Disk Diffusers
City of Gresham WWTP
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Linear Motion Digester Mixers
 Replace aging
biogas mixing
system (3 - 40 hp
compressors)
 Install Linear Motion
Mixers (LMM) for
both digesters
 Each LMM has 20
hp motor and VFD
 Currently operating
at 75% speed and 5
hp.
 Essentially trading
80 hp 24 hrs/day for
10 hp 24 hrs/day
City of Gresham WWTP
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Linear Motion Mixer (Inside Digester)
HydroDisk Diameter 8 feet
Travel (up and down) 20 inches
30 cycles/minute
City of Gresham WWTP
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FOG Receiving Station, Phase 1, 2012
 10,000 gallon FOG Receiving Tank
 FOG Grinder, FOG Unload/Tank Mixing Pump and FOG
Feed Pump
 FOG Heat Exchanger using Cogen Hot Water Loop
City of Gresham WWTP
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FOG Receiving Station, Phase 1, 2012
 Advertised RFP for FOG Haulers
 3 FOG Haulers Contracted – must be Preferred Pumpers
 8 cent per gallon tipping fee
 7,500 gpd received during phase 1 – small tank difficult to
operate effectively
City of Gresham WWTP
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Energy Net-Zero Project, Phase 2A
FOG Receiving Station Expansion, 2014
 Added 20,000 gallon receiving tank
 30,000 gallon total capacity as of April, 2014
 Major Increase in Biogas Production, now receiving
12,000 gpd, $300,000 in tip fees in 2015
City of Gresham WWTP
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Energy Net-Zero Project, Phase 2B:
400 kw Cogeneration Expansion
 The flared biogas to be utilized in additional 400 kw
Cogenerator 2
 $2.8 million design and construction
 $1.4 million in grants
 Completed January, 2015
City of Gresham WWTP
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Energy Net-Zero Project, Phase 2B
400 kW Cogeneration Expansion
Energy Building ?
COGEN 1
COGEN 2
City of Gresham WWTP
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Biogas Production Trends
Biogas (SCF/day) and FOG Injection (Gal/day)
350,000
12,000
Cogen 2 Phase 2B
300,000
10,000
FOG Phase 2A
250,000
200,000
8,000
FOG Phase 1
6,000
150,000
4,000
100,000
2,000
50,000
0
0
2010
2011
2012
Biogas
2013
2014
2015
FOG
 2014 Gas production up 60%+ from baseline
 Produced more energy than we consumed in 2015
 Flared 20% of biogas production in 2015 (Future project?)
City of Gresham WWTP
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Biogas Scrubbing Required for Successful Cogen
City of Gresham WWTP
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Biogas Scrubber Media
 Largest Cost of the treatment system
 H2S Iron Sponge Media replaced every 60-120 days
 H2S media changed when treated biogas > 100 ppm
 Siloxane media Changed every year (switch tanks 6
months)
 1 per year siloxanes testing, unreliable and expensive
 Storage required for media so it is ready to go
 Change cogen oil (if needed) when media is replaced for
½ day outage.
 $10,000 per H2S Media Changeout (3 per year)
 $6,600 per Siloxane Media Changeout (1 per year)
 About $0.01 per kWh O&M cost
City of Gresham WWTP
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March 2015 – first net zero month
March 2015
Net-Export 68,000 kwh
NET-IMPORT
NET-ZERO
NET-EXPORT
 This is possible with a net metering agreement with
PGE
 Need special Net Metering Meter (installed by PGE)
City of Gresham WWTP
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No electricity purchased from PGE since
February, 2015 - Energy Net-Zero Goal Met!
City of Gresham WWTP
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Annual Energy Trends Since 2005
Gresham WWTP Power 2005-2015
Consumption and Production
Production and Consumption (kWh)
7,000,000
6,000,000
Net-Exporter
5,000,000
Solar
4,000,000
Cogen 2
3,000,000
Cogen 1
Consumption
2,000,000
1,000,000
0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
 17% reduction in Power Consumption
 One Year of Energy Net-Export in March, 2016
 0 kWh PGE Utility Bill each month for a Year
 595,000 kWh of Net-Exported power donated to PGE
(worth $22,000 wholesale rate)
City of Gresham WWTP
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Annual Savings
10-Year Avoided Utility Costs and
2005-2015 Consumption
and
Production
FOG Tipping
Fee
Income
$800,000
$700,000
Net-Exporter
Cogen 1
Annual Savings/Revenue
$600,000
Cogen 2
FOG
Solar
$500,000
$400,000
$300,000
$200,000
$100,000
$0
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
 Approximately $750,000 per year ongoing savings
 $3,500,000 in savings since 2005
City of Gresham WWTP
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Energy Projects Cost Summary
10 Years of Energy Related WWTP Projects
$12,000,000
$10,000,000
Gresham
$8,000,000
$6,000,000
ODOE
$5,971,934
Energy Trust
$4,000,000
$2,000,000
$2,254,938
38% $1,364,147
$0
 Energy Trust Technical Assistance and Incentives
 State of Oregon BETC Program
 State of Oregon CHP Business Energy Incentive
City of Gresham WWTP
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Cogeneration O&M Costs
O&M Cost per kWh
¢ 9.0
400 kw Cogeneration O&M
Cost Summary
¢ 8.0
BiogasTreatment
¢ 7.0
Cogeneration
¢ 6.0
Avoided Utility Rate
Net-Exporter
¢ 5.0
¢ 4.0
¢ 3.0
¢ 8.0
¢ 1.2
¢ 2.0
¢ 1.0
¢ 2.1
¢ 0.0
2005 thru 2014
 About $0.03 per kWh O&M Costs
 Includes Labor & Materials for O&M.
City of Gresham WWTP
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Awards and Recognition
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2015 OR APWA Environmental
Project of the Year
2015 American Biogas Council
Project of the Year Award
2014 Clean Energy States
Alliance, State Leadership in
Clean Energy Award
2015 ACWA Outstanding
Member Agency
2015 Recognized in EPA report
on Sustainable Water Future
City of Gresham WWTP
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Questions?
Jeff Maag, Project Manager, Wastewater Services Division, City of Gresham
Jeff McCormick, Project Manager, Carollo Engineers
City of Gresham WWTP
33