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DEVELOPMENT OF AN
INTEGRATED HAULED
WASTE PROGRAM
Royce Hammitt, Des Moines Wastewater Reclamation Authority (WRA)
Des Moines Wastewater
Reclamation AuthorityAltoona - Ankeny - Bondurant - Clive - Cumming - Des Moines -
Greenfield Plaza/Hills of Coventry - Johnston - Norwalk - Pleasant Hill –
Polk City - Waukee - West Des Moines - Polk and Warren Counties -
Urbandale/Windsor Heights and Urbandale Sanitary District
Working together to protect
public health and enhance the
environment by recycling
wastewater and being the
preferred treatment facilities
for hauled liquid wastes
Operating Contractor - City of Des Moines
8/19/14 Midwest Governor's Association Tour 2
• The Des Moines WRF serves a population of 500,000
• Treated nearly 26 billion gallons of wastewater or about
72 million gallons per day in 2009
• Actively seeks to improve efficiency in use of resources
8/19/14 Midwest Governor's Association Tour 3
Water19%
Aviation10%
Building Services
7%
Civic Center3%
Library1%
Misc1%
Parks3%
Street Lights30%
Traffic3%
Wastewater23%
8/19/14 Midwest Governor's Association Tour 4
Water and Wastewater Demands Energy
Source: Texas Comptroller of Public Accounts
Typical Large City Electrical Usage
Wastewater Plants Can Produce Enough Electricity to
Meet Demands
8/19/14 Midwest Governor's Association Tour 5
Aeration and
other liquid
processes
Solids processes
Pumping
Lighting
Anaerobic
digestion of
wastewater solids
Additional energy from
biosolids and other
renewable sources
Electric Demand Potential Electric Supply
Other organic waste
including FOG (fats, oils,
and grease)
Source: David L. Parry, CSWEA, Oct. 2010
A Wastewater and Organic Waste Treatment
Center
8/19/14 Midwest Governor's Association Tour 6
Hauled organic wastes account for 42% of the feed to the
anaerobic digesters
Des Moines Wastewater Treatment Plant, Des Moines, IA
Hauled Wastes• Sources
• Sludges from regional
WWTP’s
• Industrial and food
processing wastes
• Issues• Spikes in biogas
• Foaming
• Received 24/7!
8/19/14 Midwest Governor's Association Tour 11
Original Trucked Liquid
Waste (TLW)
• Little storage
• Loads transferred to
digester as they arrive
and unload
New TLW Facility
• Storage
• 160,000 gallons
• Carry over of wastes
through weekend
• Costs less to store feed
stock than to store gas
8/19/14 Midwest Governor's Association Tour 12
COMBINED HAULED WASTE
PROJECT RESULTS
• Tanker unloading time
reduced by 50%
• Areas of congestion
eliminated
• Customers (haulers)
give positive comments
8/19/14 Midwest Governor's Association Tour 15
8/19/14 Midwest Governor's Association Tour 18
0
100
200
300
400
500
600
700
800
900
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
x 1
00
0 g
all
on
s
Restaurant Grease Hauled to WRF
FY13
FY12
FY11
FY10
FY09
FY08
FY07
FY06
Tasks & Objective of the BioEnergy
Master Plan
8/19/14 Midwest Governor's Association Tour 20
Enhance biogas
production
Maximize use of
biogas
Develop Economic Model
Improve digester
facilities
Reliable,
Flexible System
for the Future
EvaluationProcess
WRA’s Existing Program
8/19/14 Midwest Governor's Association Tour 21
AnaerobicDigestion
BiogasStorage
50 MGD
0.14 MGD
Sludges
Hauled Wastes
Biosolids to Land Application
Process Heating
Building Heating
Power Generation
Industrial User
Primary and Secondary Treatment
> 30 loads/day
0
250,000
500,000
750,000
1,000,000
1,250,000
1,500,000
1,750,000
2,000,000
2,250,000
1/8/07 2/27/07 4/18/07 6/7/07 7/27/07 9/15/07 11/4/07 12/24/07 2/12/08 4/2/08 5/22/08 7/11/08 8/30/08 10/19/08
Cu
.Ft
/ D
ay
Date
Total Production
Total UsageObjective < 5% loss
Daily Biogas Production and Usage
8/19/14 Midwest Governor's Association Tour 22
Evaluation Process
• 11 economic and noneconomic criteria
• WRA staff developed weighting
8/19/14 Midwest Governor's Association Tour 23
0 25 50 75 100
Weight
Ease of O&M
Proven and Reliable
Lifecycle Costs
Task 1
8/19/14 Midwest Governor's Association Tour 24
Improve digester
facilities
Reliable,
Flexible System
for the Future
EvaluationProcess
Required Digester Improvements• Covers Evaluated
8/19/14 Midwest Governor's Association Tour 25
Fixed Steel Floating Gas Membrane
Submerged Fixed
Concrete
Submerged Fixed Cover Gas Dome
8/19/14 Midwest Governor's Association Tour 26
Gas Withdrawal
Gas Dome
Spray Nozzles
EmergencyLiquid Level
Overflow toStandpipe
NormalOperatingLevel
Normal Overflow to Standpipe(Embedded in Cover) Emergency Overflow
Pipe to U-Tube Gas Seal
3" Gas Pipeto Standpipe
Recirculation fromTank Bottom
Transflow3-Way Valve
Pressure VacuumRelief
Digester Covers Selected• Primaries – Submerged Fixed Covers
• Ease of O&M
• Foam control
• Increased capacity (~8%)
8/19/14 Midwest Governor's Association Tour 27
• Secondary – Gas Membrane– Biogas storage
– Biosolids storage
– Dewatering operations flexibility
Task 2
8/19/14 Midwest Governor's Association Tour 29
Enhance biogas
production
Improve digester
facilities
Reliable,
Flexible System
for the Future
EvaluationProcess
Methods Evaluated for Increasing Biogas
Production
• WAS pretreatment
– MicroSludge®
– OpenCEL
• Advanced digestion– Extended thermophilic
– Temperature phased (TPAD)
8/19/14 Midwest Governor's Association Tour 30
Conclusions for Enhancement Evaluation
• WAS Pretreatment• Limited benefit due to small fraction of TWAS
• Potential increase in biogas production ~ 7%
• Payback > 20 years
• Advanced Digestion• Increased capacity & Class A product
• Potential increase in gas production ~ 10-15%
• Payback >15 years
• Best Option• Increase hauled waste volume
8/19/14 Midwest Governor's Association Tour 31
Task 3
8/19/14 Midwest Governor's Association Tour 32
Enhance biogas
production
Maximize use of
biogas
Improve digester
facilities
Reliable,
Flexible System
for the Future
EvaluationProcess
Biogas Storage Evaluation
8/19/14 Midwest Governor's Association Tour 34
Capacity
(cf)% of Biogas Flared
Current Future
475,000 6.1 13.8
805,000 5.8 13.6
Increased
storage is
important, but
not the key!
Natural Gas Use
Alternatives for Increasing Use
• Replace natural gas use at plant
– Supply additional boilers
– Produce biomethane for plant-wide use
• Produce additional power• More operating time
• Additional engine generators
• Sell to gas utility
• Increase volume sold to industry
8/19/14 Midwest Governor's Association Tour 35
Boilers
Misc.
Other
8/19/14 Midwest Governor's Association Tour 37
Additional Generation
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1,400,000
1,600,000
1,800,000
Jun'13
Jul '13 Aug'13
Sep'13
Oct'13
Nov'13
Dec'13
Jan'14
Feb'14
Mar'14
Apr'14
May'14
KW's Purchased vs Generated
Purchased 19,424,008 Generated 12,758,651
Generated:Average: 39.6%Last Month: 44.7%
Current Engines
8/19/14 Midwest Governor's Association Tour 38
• 3 engine
generator sets,
each ~600 kW
• In 2010, used
over 190 million
cubic feet of
digester gas to
generate
almost 10
million kWh of
electricity
Compressed Biogas (CBG) Production
Options
• Pressure Swing Absorption (PSA)– Low energy (~60KW)
– Experience with biogas
– Operational flexibility
• CO2 Wash– High energy (~300KW)
8/19/14 Midwest Governor's Association Tour 40
Use of Biogas by Local Industry
• Averaging 700,000 cfd
• Capacity of 1,200,000 cfd
• Conveyance system limits
• Potential for 1,700,000 cfd in future
8/19/14 Midwest Governor's Association Tour 41
Staged Approach to Expanding Biogas Use
• Increase industry use preferred• Proven, reliable
• Minimal affect on O&M
• Backup power generation associated with High
Rate Treatment Facility (separate project)• Add 4 new 1.4 MW engine generators (2 CHP biogas, 2
Emergency)
• Use in boilers possible in future• Proven, reliable system
• Reduces natural gas dependence
• Payback ~ 12 years
8/19/14 Midwest Governor's Association Tour 43
Task 4
8/19/14 Midwest Governor's Association Tour 44
Enhance biogas
production
Maximize use of
biogas
Develop Economic Model
Improve digester
facilities
Reliable,
Flexible System
for the Future
EvaluationProcess
Process & Economic Model
8/19/14 Midwest Governor's Association Tour 45
Model
Primary& WAS
4 Different
Wastes
Digestion process
parameters
PowerNatural Gas
Tip FeesTreatment CostsLand Application
DewateringBiogas Options
Monthly Biogas Balance
Present Worth
OutputInput Parameters
•Reliable systems to
provide valuable
public services
•Increased revenue
potential
•Flexibility for multiple
uses of biogas will be
critical
8/19/14 Midwest Governor's Association Tour 49
Digestion / Biogas System Improvements will
Enhance WRA’s Overall Sustainability