Turning Waste Into Energy
Dallas Water Utilities
Southside Wastewater Treatment Plant
Cogeneration and Co-Digestion Projects
May 9, 2011
Outline

What is Cogeneration

Biogas and It’s Uses

Cogeneration Project Details

What is Co-Digestion

Grease Trap Waste and How It Can Be Used

Future of Co-Digestion at SWWTP

Questions and Answers
2
What is Cogeneration?

Cogeneration is the production of two types of
energy such as heat and electricity from one fuel
source in such a way that both are useable
Recoverable
Mechanical Energy
Unrecoverable
Waste Heat
35%
22%
43%
Recoverable
Waste Heat
3
What is Biogas?

Biogas is the methane (CH4)
produced as a by-product of the
anaerobic digestion process at
the Southside Wastewater
Treatment Plant

DWU’s biogas was used to fire
boilers to heat the digesters, but
a large portion was burned off
in flares

Biogas is a renewable fuel
source that can be used to
generate electricity in lieu of
using coal or natural gas
4
How Can Biogas Be Used?
Screenings
Removal
Grit
Removal
Primary
Clarification
Aeration
M
Raw
Sewage
Secondary
Clarification
Filtration
M
Treated
Effluent
Screenings
Grit
Primary
Sludge
Secondary
Sludge
Gas
Flare
Gas
Storage
Gas
Compression
Digesters
Heat and
Power
Generation
In lieu of current operations
where a majority of the
biogas is flared, the biogas
can be sent to the
generation facility for the
production of electricity and
hot water.
Hot Water
Supply and
Return Lines
5
As a fuel to generate electricity, DWU’s Biogas
has the potential to reduce the City of Dallas’
total grid derived electricity consumption by
almost 4%
7% Reduction
(30,000,000 kWh/Year)
60% Reduction
(30,000,000 kWh/Year)
DWU
SOUTHSIDE
WWTP
430,000,000 kWh / Year
50,000,000 kWh / Year
4% Reduction
(30,000,000 kWh / Year)
CITY
790,000,000 kWh/Year
6
Treatment Plant / Cogeneration Site Layout
Cogeneration
Site
Electrical
Biogas
Hot Water
7
Renewable Energy Leasing Project Details
DWU RESPONSIBILITY
WH
Southside
WWTP Main
Substation
To WWTP
Loads
LESSEE/DEVELOPER RESPONSIBILITY
Meter
To/From
Oncor
WH
Natural
Gas
Biogas Supply
Meter
DWU RESPONSIBILITIES
• Provide Utility Connections
• Produce Guaranteed Quantity
and Quality of Biogas
• Purchase Electricity
• Utilize REC’s
Meter
Southside
Digesters
Meter
Guaranteed
Gas
Compression
From
Oncor
Gas
Storage
WH
Hot Water
Supply and
Return
Meter
L/D RESPONSIBILITIES
• Design/Build/Finance/Operate
Cogeneration Facility
• Generate/Deliver Electricity
• Generate/Deliver Hot Water
• Permit Facility
• Capitalize on Rebates/Tax Credits
8
Benefits of the Project

The City will reduce its grid derived electricity needs
by 30,000,000 kWh per year

Reduced cost of electricity will result in annual
savings of approximately $1,500,000/year

Project will generate approximately 30,000 Renewable
Energy Credits (REC’s) per year.

The REC’s generated may also be used towards
LEED’s certification.

No need for additional labor or skill set above staff’s
current capabilities

Project will reduce region wide emissions
9
Co-Digestion
10
What is Co-Digestion?
$
Biogas
Co-generation
High Strength
Wastes
Solids from
Wastewater
Treatment Plant
Digesters
Receiving facility
Solids
Dewatering
Land Application
11
High Strength Wastes and Related Gas Production
Grease Trap Waste
660
Restaurant Waste
Food Waste
Raw Sludge
165
Brewer's Grain
Sugar Cane
Brown Grease yields
4x the amount of gas
as WWTP solids
Poultry
Cattle Manure
Methane Yield, ft3gas/per ton
12
Grease Trap Waste (Brown Grease)

First phase of Co-digestion to focus on brown grease

Items yet to be determined
– Amount of grease that can be digested
– Hauling to the plant site
– Effects on the Cogeneration Facility

If successful future phases
will include other high strength
wastes
13
Benefits of Brown Grease Digestion

Increase in biogas production, electricity and hot
water
– 75,000 gallons/day = $760,000/year

Potential revenue from tipping fees
– 75,000 gallons/day = $1,600,000/year

Increased solids destruction
14
Benefits of Brown Grease Digestion (cont’d)
1 ton
1 ton
23 tons GHG
0.8 tons of GHG
1 MW of Electricity
15
Potential Drawbacks

Increased digester maintenance will be necessary to
prevent clogging in the mechanical systems

Digester upsets due to foreign and/or toxic
substances

Increases in truck traffic could pose a nuisance to the
surrounding neighborhood

Expansion of the Cogeneration Facility will adversely
impact air quality and air permitting at the plant
16
Treatment Plant / Cogeneration Site Layout
Cogeneration
Site
Digester
Feed Line
Grease Receiving
Facility
17
Co-Digestion Details

Cost is anticipated to be around $3 million dollars

Expected payback
is 2 years

Design RFP and
Grease Hauling
RFP are both
scheduled for
August 2011
18
Questions?