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S c i e n t i f i c a n d T e c h n i c a l C o n f e r e n c e
Extraction and Use of Renewable Thermal Energyfrom Small Wastewater Systems, Best Practices
Platinum Sponsor Silver Sponsor
W A T E R S E R V I C E S A N D T H E N E W E N E R G Y C H A L L E N G E S
P r e s e n t e d b y M i k e M e h a f f e y , P. E . , G a n n e t t F l e m i n g , I n c .
A u t h o r : M a r k P i c k e r i n g , G a n n e t t F l e m i n g , I n c ,
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Thesis
New equipment designs now allow smaller (2,500m3/day30,000 m3/day) wastewater systems to achieve net positive
energy using anaerobic digestion
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Discussion TopicsTypes and Uses of Wastewater Energy
Basic Types of Sludge Stabilization
Sludge Stabilization Energy Balance
Best Design and Operations Practices: Anaerobic Digestion
Case Study: Danville, Pennsylvania, USA
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Wastewater is an Energy Resource
Chemical Energy inUntreated Wastewater
12-15 Mbtu/kg COD
Chemical Energy inPrimary Sludge, dry
15-15.9 Mbtu/kg TSS
Chemical Energy inSecondary Biosolids, dry
12.4 13.5 Mbtu/kg TSS
Thermal Energy @ 3,500m3/day, 15C
220 Mbtu
Thermal Energy @17,500 m3/day, 15C
1,099 Mbtu
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Sludge Chemical Energy Anaerobic Digestion
Most Common:Mesophillic, 2-Stage
4.2 L biogas per kg VSS
converted Biogas = 640 ppm CH4
Gas Combustion inboiler or Combined
Heat and Power (CHP)Generator
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Anaerobic Digestion is the Greatest Source of
WWTP Renewable Energy
Small WWTP Applications Common for Primary Treatment
WWTPs
Smaller systems need supplementalfuel for colder weather digestion
Can treat contract waste to increasegas formation
Limited CHP Potential but can bethermally self-sufficient
Large WWTP Applications Thermal self-sufficient
Excess gas for CHP Net Positive WWTP Energy Profile
0
10
20
30
40
50
60
70
80
19
60
70
76 77
Number with
Anaerobic
Digesters
Size Range, m3/day
Survey of Small WWTPs in U.S.
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Anaerobic Digestion Has a Smaller NetEnergy than Aerobic Digestion
*Average Day, Summer
**Standard Practice for Mixing and Pumping Energy
Can anaerobic digestion be net energy positive?
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Optimal Equipment Selection Can Achieve Net Energy Goal
Pump+Nozzle Mixing Efficient mix, Lower Operating
Times
Linear Motion Mixer
Up to 70% smaller motor High Efficiency Heat
Exchange
Biogas Storage
Membrane
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Best Practice Chemically Enhanced PrimaryTreatment
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Summary of Anaerobic Digestion Practices
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Case Study: Danville, PA, U.S.A.
14,000 m3/day Design Flow 2-Stage, Mesophillic Anaerobic Digestion
Removal of Primary Sludge and WAS throughPrimary Clarifiers
Connected Loads and Physical Plant Used toModel Energy Balance
Average Monthly Temperatures Used to Model
Heat Input to Sludge Compared Standard and Best Practices
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Temp Impact on Digester Net Energy
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Best Practices Can Achieve Net
Positive Energy Balance
(10,000)
(8,000)
(6,000)
(4,000)
(2,000)
-
2,000
4,000
6,000
8,000
10,000
ProcessEnergy,MBtu
Standard
Best Practice
Model Data
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Optimal Equipment at Small WWTPs
Yield Valuable Benefits Increases Renewable Energy Yield
Reduces Greenhouse Gas Emissions
Produces a more stable sludge
Reduces Operating Costs
A more sustainable solution
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Questions?
Mike Mehaffey