1. DIGESTION: MANAGING
BLENDED WASTES
ROBERT CASE – CITY OF FLINT
WATER POLLUTION CONTROL SUPERVISOR
CHAD ANTLE – BIOWORKS ENERGY
CHIEF EXECUTIVE OFFICER

2. CITY OF FLINT
WATER POLLUTION CONTROL, 2008

3. Flint’s Solids Handling, 2008

4. PUBLIC – PRIVATE PARTNERSHIP
2008
Began with Governor’s Trade Mission
 Center of Energy Excellence with Kettering University
 Energy Production – Major Goal
 MEDC Grant + SBI Funding = Capital Improvements
 Processing Cost Savings Provides Operating Revenue

5. CITY’S GOALS AND OBJECTIVES
Reduce operating
costs
Minimize capital
expenditures
Maintain or
enhance reliability
of solids
processing
Promote
sustainable
operations

6. SWEDISH BIOGAS INTERNATIONAL
GOALS AND OBJECTIVES
Implement Digestion Process
Produce Energy - Biogas
Business Expansion, Revenue Increase
Rehabilitation of Flint’s Solids Facilities

7. FLINT BIOGAS PLANT - PHASE I
Ground
breaking
08/09/2010
Seed sludge
loading
05/16/2011
• Production
startup
• Cost
savings
begins
08/2011
Thru
09/2011
Ex. North Digester
Existing
Biosolids
Incinerator
Biogas
Digestate
Storage
Sludge
from
Treatment
Plant
Digested
Biosolids to
Incinerator
Gas
Holder
Digestate
Storage
To Boiler

8. ACCOMPLISHMENTS
2011
REFURBISHED NORTH DIGESTER
• NEW MIXING SYSTEM
• NEW HEATING SYSTEM
• NEW CONTROL SYSTEM
REPLACED GAS SPHERE WITH NEW
DIGESTATE STORAGE TANK
NEW PUMP HOUSE
NEW SLUDGE FORCE MAINS
NEW CENTRIFUGES

9. SBI revenue depends on cost
savings
Cost savings declined
•Lower sludge volume
•Reduced natural gas cost
Value of Biogas
City forced
to
abandon incineration
Unexpected
Changes

10. THE NEW ORDER
SBI exits
North
America
operations
BioWorks
Energy
acquires
N. America
operations
BioWorks
negotiates
new contract
with Flint
 Stable and Sustainable Revenue Base
 Long Term Commitment to Partnership

11. I
• Landfilling to replace incineration
• Use biogas to generate lower electricity costs
II
• Enhance biogas production – pursue outside wastes
• Blend high energy outside wastes with dilute municipal sludge
III
• Digest the blended wastes
• Produce electricity with internal combustion engine generator
STEP BY STEP: The New Order

12. ADVANTAGES
Greatly
increased
gas
production
Increased
revenue
Tipping
fees
Diversion
of high
strength
wastes
Improved
utilization
of assets

14. Flint Solids Handling, 2015
Municipal Biosolids
High Strength Wastes

15. 2015 GOALS
INCREASE VOLUME
OF EXTERNAL
SUBSTRATES
INSTALL
ELECTRICAL POWER
GENERATION
CONSTRUCT
BIOSOLIDS
LOADING FACILITY
DECOMMISSION
INCINERATION

16. BLENDED WASTES
MUNICIPAL WWTP SLUDGE
(PRIMARY, WAS, TWAS)
1 to 8% total solids
60 to 90 % Volatile Solids
55 to 65% Methane Content
Heterogeneous MIX – Good for Digestion
Relatively Low “Energy Density”
Contains both MACRO/Micro Nutrients required for
stable process
EXTERNAL SUBSTRATES
(FOOD PROCESSING WASTES, ORGANIC PROCESS, ETC)
TS% - Large Variations, Rheology Not Directly
Related to TS%
30 to 100% Volatile Solids
45 to 75% Methane Content
Homogeneous Mix – Can Be Difficult to Digest as a
Mono-Culture
Higher Energy Densities Than WWTP Sludge
May Lack Macro/Micro Nutrients
Proper Combination of the Two - Better Than Either Component

17. Increased gas
production
Micro-
Biological
diversity
Potentially higher
degradation of solids
Increased
revenue
(Tip fees,
power
generation)
BENEFITS
OF
BLENDED
WASTES
How do I
put it
together?
REALLY…
Is this
necessary?

18. ADMINISTRATIVE CONCERNS
Substrate
Variability
• Unknown
factors
• Unwanted
effects
• NPDES
compliance
• Polymer
consumption
Delivery
• Acceptable
transfers
• Limited
delivery
window
• Labor
resources
Sustainability
• Must achieve
desired results
• Reliable Staff
• Who is the
“Cavalier”?

19. PROCESS CONCERNS
SUBSTRATE VARIABILITY
The Unknown and Sometimes Unwanted Impacts
IMPACTS
Thickening and
dewatering
performance may
vary
RESPONSIBLITY
Owner must insure
compatibility with
digestion system
and NPDES limits
TESTING
Substrates should
be tested prior to
system injection,
before problems
arise
SUBSTRATE
PROVIDER
Not responsible for
the WWTP.
Responsible only to
get rid of their
waste reliably.
QUANTIFY
Recycle Streams
and nutrient Loads
should be projected,
with testing and
modeling

20. GAS QUANTITY/QUALITY CONCERNS
• Flow Rates
• Pressure/Vacuum Relief Valves
• Flare
• Gas storage
• Water separation
GAS HANDLING
SYSTEM
DESIGN
• Changes in energy content
• Increases in Hydrogen Sulfide
• Dilution of siloxanes (mg/M3)
• Higher chemical (Carbon/F3Cl2) costs
BIOGAS
QUALITY

21. STEADY SUBSTRATE SUPPLY
• Not always as advertised!
• Marketing and procurement of long term contracts
• Competitive pricing
• Economic Development – Educate
planners/administrators of the benefit potential
MANAGEMENT
• Sufficient daily supply
• Long term contracts – Hard to come by
• Tip Fees are Volatile – competition for substrates
• Educating administrators regarding the entire process
CHALLENGES
• Must be “Right-Size” for efficient processing
• Under utilization of capital improvements if substrates
don’t materialize
• Laboratory QA/QC of Substrates – Insure material is as
planned
RISKS

22. PRACTICAL ISSUES OF
BLENDED WASTES
Proportions of the desired mix and how to achieve it
Order of addition (Municipal sludge versus
substrates)
Higher gas production than expected
Rapid Rise – Underestimated gas production +
insufficient Mixing = rapid expansion in gas/liquid
matrix
Flaring of gas instead of power generation = lost
revenue

23. ECONOMICS OF BLENDED WASTES
Tip Fees
Additional
Energy
Production
• Power
production
• Avoidance of
natural gas
usage
• Renewable
energy
credits
Added
nutrient value
for land app
Higher
energy
consumption
through
higher mixing
requirements
+/- Impacts to
residuals
processing
Recycle
streams –
impacts to
plant
Increased
employee
labor

24. QUESTIONS?