1. Co-Digestion – The Path to Success
Template Revised 15 March 2011
November 2015
Blair Wisdom

2. Agenda Co-Digestion Overview Feasibility
Ensure Success of Receiving Stations and Pretreatment
Safeguard for Stable Digester Performance

3. Co-Digestion overview

4. Black & Veatch | November 2015
What is Co-Digestion?
It takes shape in many forms. Essentially, it is the addition of high strength waste (HSW) to anaerobic digesters
Commonly practiced with the brown grease (BG) portion of fats, oils, and grease (FOG)
Increasing focus on industrial and pre- consumer wastes
Dairy whey
Fruit/vegetable wastes
Institutional food wastes
Corn silage

5. Why would you Co-Digest?
Black & Veatch | November 2015
Why would you Co-Digest?
Excess capacity in digesters may afford opportunity for revenue from tip fees.
Regional haulers (FOG and others) may need an outlet (encourage them to keep it out of collection system.
Control where HSW are injected in plant – turn from waste that consumes energy to an enhancement
Increased load can make energy recovery more attractive
Energy

6. stabilization technologies
Black & Veatch | November 2015
Organic Resources-to-Energy CO-LOCATION/(CO)-DIGESTION AND GAS UTILIZATION
Sludge
WWTP
EXISTING DIGESTERS
CO-GEN
GRID
DEDICATED
DIGESTERS
GAS
UPGRADING
RNG
FLEET
PIPELINE
stabilization technologies
COMMERCIAL
ORGANICS
SOURCE SEPARATED ORGANICS/ ORGANIG FRACTION
OF MSW
FOG

7. Co-Digestion Can Enhance Overall Sustainability
Black & Veatch | November 2015
Co-Digestion Can Enhance Overall Sustainability
Reliable systems provide valuable service to industries
Increased revenue
On-site power production provides greater reliability
Flexibility for multiple energy uses

8. Pros/Cons of Co-digestion
Black & Veatch | 2 September 2015
Pros/Cons of Co-digestion
ADVANTAGES
Synergistic effects (location, infrastructure)
Qualified & experienced personnel on site
Improves digester performance thanks to symbiotic behaviors
Increase in revenues through tipping fees
Self-sufficient generation of renewable energy
on-site achievable
Biosolids contain less contaminants, more nutrients, and are more suitable for agricultural use than conventional biosolids
Increased in gas production and quality
Improved economics, benefitting rate payers for publically owned treatment works +
stabilization technologies
Co-digestion dilutes the inhibitory effects of substrates, balance the micro and macronutrients, increase the organic loading with consequent higher methane yields per unit of digester volume; lastly diversify and synergize the microbial communities which play pivotal role in the methanogenesis.
Source: Braun, Wellinger (2003); Grasmug, Braun (2003); Schmelz (2007); STOWA, (2006) adapted

9. Pros/Cons of Co-digestion
Black & Veatch | 2 September 2015
Pros/Cons of Co-digestion
DISADVANTAGES
Capital costs; feedstock receiving station and conditioning/removal of contaminants before feeding digester and increased mixing may be required
Increased chemical oxygen demand (COD)/nutrient load of digestate’s filtrate
Foam formation and scum layers in digester
Odors
Dewaterability: increased amount of biosolids
Hygienization may be required
Deposition of material (pipe & valve blockage; reduced digester volume)
Mixing Challenges -
stabilization technologies
Source: Braun, Wellinger (2003); Grasmug, Braun (2003); Schmelz (2007); STOWA, (2006) adapted

10. Feasibility

11. Process Capacity

12. Rock River Water Reclamation District
Black & Veatch | November 2015
Rock River Water Reclamation District
Drivers:
Combat rising energy costs
Institute sustainable practices
Fully utilize equipment capacities
Capacity evaluation:
Average 32 day SRT
100 ppd of VS/kcf

13. Rock River Existing Stabilization and Gas Handling
Black & Veatch | November 2015
Rock River Existing Stabilization and Gas Handling
Excess Gas Treatment Capacity
Excess Digester Capacity
Excess Engine Generator Capacity
Limited Gas
Handling Capacity

14. Availability of HSW

15. Significant Biogas potential in high strength wastes
Black & Veatch | November 2015
Significant Biogas potential in high strength wastes

16. Organic Feedstocks & Properties for AD
Black & Veatch | November 2015
Organic Feedstocks & Properties for AD
MANURE, SEWAGE SLUDGE; FOOD PROCESSING WASTE
INDUSTRIAL SLUDGE
(e.g. Thin Stillage from EtOH Production); BG (FOG)
SLAUGHTER HOUSE WASTES
COMMERCIAL FOOD WASTES
(Restaurants; Cafeterias)
COMMERCIAL FOOD WASTES (Groceries; Packaged Waste)
RESIDENTIAL SOURCE SEPARATED ORGANIC
WASTE; ORGANIC FRACTION OF MSW
Increase in total solids (TS) content
Decrease in homogeneity
Increase in contamination (non-digestible)
stabilization technologies

17. Area Specific HSW Survey industries in service area
Black & Veatch | November 2015
Area Specific HSW
Survey industries in service area
Evaluate characteristics & value of available wastes pH
Total and Volatile Solids (TS and VS)
Total and Soluble COD
Total Ammonia Nitrogen (TAN)
Total Kjeldahl Nitrogen (TKN)
Volatile Fatty Acids (VFA)
Long Chain Fatty Acids (LCFA)
Alkalinity
Gas Production and Composition
Capillary Suction Time (CST) and Sludge Dewatering
Biosolids Odors
Determine loading and any adverse effects

18. Increased Competition for FOG – Long term outlook?
Black & Veatch | November 2015
Increased Competition for FOG – Long term outlook?
Increased interest in yellow grease for biodiesel
Gasoline price fluctuations
Carbon footprint/offsets
Increased use of yellow grease in
Animal feed
Cosmetics
Increased consideration as substrate for industrial anaerobic Digestion
Grant/offset benefits
Renewable energy generation
Reduced restaurant generation from recession
Pricing to attract haulers
3rd bullet is most applicable to plant
JB: FOG is the term under which brown grease (BG) and yellow grease (YG) falls; typically only BG is used for co-digestion whereas YG is increasingly used for biodiesel production due to its higher purity/value; YG is typically not used for co-digestion; the trend I have seen is that rendering firms that collect the BG try to discharge the BG for the lowest price; so if one WWTP’s receiving fee is too high then they go to another receiving place where the cost per gal is lower = WWTPs may start to compete for haulers; best to have long-term contracts with less haulers in place if possible to secure supply

19. Commercial and Residential Source Separated Organics - Co-Digestion
Black & Veatch | November 2015
Commercial and Residential Source Separated Organics - Co-Digestion
OBJECTIVES & MEASURES:
Increase of Waste Diversion towards Zero Waste Goal (meet local, state and federal landfill diversion and/or organics ban requirements)
Closing Carbon and Nutrient Loop
Cheap and plentiful feedstock for energy production
Educate food establishments, food processors, retailers, and residents of organics collection
stabilization technologies

20. Availability of HSW Contacted 50 companies in surrounding area
Black & Veatch | November 2015
Availability of HSW
Contacted 50 companies in surrounding area
Conclusions of HSW Survey
Abundant supply of Non-FOG high strength wastes
Thin stillage, dairy wastes, distillers syrups
4,000 to 5,000 gallons per day of FOG waste generated within the district’s service area
Another 20,000 gallons per day of FOG waste generated Around the district’s service area
Adequate Supply for 20,000 GPD HSW Facility

21. Assess the Benefits

22. What are the Operational Costs and Benefits?
Black & Veatch | November 2015
What are the Operational Costs and Benefits?
Operational Costs
Some added maintenance
Added loads to the plant
Potentially added biosolids disposal costs
Operational Benefits
Increased biogas
Increased waste heat from engine generators
Tipping fees
Service to customers
B&V - 22

23. Ensure Success of Receiving Stations and Pretreatment

24. Hauling Considerations
Black & Veatch | November 2015
Hauling Considerations
What type of wastes are being processed?
Processed source separated food wastes?
“Liquid” high strength wastes?
Efficient truck unloading
Hauling schedules?
Multiple trucks at a time?
Cleaning stations
Weigh scales
Hauled load management and billing

25. Pre-treatment and materials handling issues
Black & Veatch | November 2015
Pre-treatment and materials handling issues
Pretreatment: Rock traps, screens, grinding, depackaging (industrial wastes)
Remove non-biodegradable materials
Protect downstream equipment
Reduce particle size to optimize digestion
Storage tanks
Mixing
Site specific heating
Heat tracing, HEX, mixing with warm sludge
JB: FYI - The slide you’re showing for Pacific Biodiesel is a demonstration plant at the Oceanside WWTP of San Francisco; the previous installation at that side funded by the CA Energy Commission with Black Gold failed to make biodiesel from brown grease; I do not know if they are actually making vehicle-fuel grade biodiesel from it or off-spec biodiesel that can be used as boiler fuel.

26. Debris in Hauled Wastes
Black & Veatch | November 2015
Debris in Hauled Wastes

27. stabilization technologies
Black & Veatch | November 2015
FOG/BG CO-DIGESTION EXAMPLE: WATSONVILLE WWTP
stabilization technologies
Source: Kester, G. (2008)
PLANT DESIGN CAPACITY: 12 MGD
FOG CO-DIGESTION: 3,000 – 10,000 GAL/DAY

28. Example – Des Moines WRA - 170,000 Gallon Receiving Tank
Black & Veatch November 2015
Example – Des Moines WRA - 170,000 Gallon Receiving Tank
JB: what facility?

29. Des Moines WRA - Receiving/Storage Tank
Black & Veatch | November 2015
Des Moines WRA - Receiving/Storage Tank
Mixed via recirculation pumps and nozzles
Lined for corrosion control
JB: what facility?

30. Black & Veatch | November 2015
Summary of receiving concepts Basic or Sophisticated Systems – No two are the same!
Simple systems with rock-boxes - traps grit/debris before larger tank
Mechanical systems for removing debris
Some have storage while others go straight to digesters
Heating? Is it needed?
CDM – rock boxes
No standard design

31. Safeguard for Stable Digester Performance

32. Opequon WRF – Frederick Winchester Service Authority (FWSA)
Black & Veatch | November 2015
Opequon WRF – Frederick Winchester Service Authority (FWSA)
Current Solids Treatment:
Lime-Stabilized biosolids – landfill disposal
Frame and Plate Filter Presses
Design Solids Process:
Two mesophilic primary digesters and one secondary digester

33. Black & Veatch | November 2015
Solids Process

34. Solids Design Summary Substrates for co-digestion: Wastewater sludge
Black & Veatch | November 2015
Solids Design Summary
Substrates for co-digestion:
Wastewater sludge
Kraft Foods waste
Dairy whey waste
GTW and DAF Float
Food waste
Solids retention time, days
Maximum Month
Annual Average 15 20
VS Loading Rate, ppd/kcf
154
132
Expected Volatile Solids Reduction, %
Average Annual 45

35. Pilot Testing - Digester Set up and Operation
Black & Veatch | November 2015
Pilot Testing - Digester Set up and Operation
4 digesters with working volume of 9.75L, 15 day SRT
Mesophilic temperature (370C)
Seeded with 8 Liters of digester effluent from Christiansburg WWTP
Schematic Diagram showing Digester setup

36. Parameters analyzed pH Total and Volatile Solids (TS and VS)
Black & Veatch | November 2015
Parameters analyzed pH
Total and Volatile Solids (TS and VS)
Total and Soluble COD
Total Ammonia Nitrogen (TAN)
Total Kjeldahl Nitrogen (TKN)
Volatile Fatty Acids (VFA)
Long Chain Fatty Acids (LCFA)
Alkalinity
Gas Production and Composition
Capillary Suction Time (CST) and Sludge Dewatering
Biosolids Odors

37. Waste Characteristics (Part II)
Black & Veatch | November 2015
Waste Characteristics (Part II)
High Strength Waste
Total COD
(mg/L) TS VS
GTW
50,000
40,000
37,000
Whey
87,000
78,000
56,000
DAF
600,000
300,000
285,000
Juice waste
76,000
44,000
43,000
Sludge Mix
~35,000
~30,000
~23,000
Part I: Feed contained Juice Waste and Whey Waste only. Digester performance was assessed and the roles of alkalinity and VFA concentrations were evaluated
Part II: Carried out in three phases with increasing concentrations of all the food wastes listed in the table above.

38. Total Time of Operation: 310 Days
Black & Veatch | November 2015
Total Time of Operation: 310 Days
The above mentioned compositions were attained on Day 180
Juice processing waste underwent a sudden, drastic change on Day 240
New waste much “stronger”
Digester 4 which was receiving the highest HSW load by volume exhibited failure

39. Volatile Solids (mg/L)
Failure Caused by Shock Load to Digester
Wastes being added were acidic in nature, especially the juice processing waste
The sudden change in the nature of the waste seems to have inflicted a “shock load” on the digester that exhibited failure
“Old” Juice waste
“New” Juice Waste pH
4.10
3.10
Total Solids (mg/L)
32,000
72,000
Volatile Solids (mg/L)
31,000
68,000
Total COD (mg/L)
66,000
208,000

40. Acidic wastes can reduce buffering capacity of anaerobic systems.
Black & Veatch | November 2015
Acidic wastes can reduce buffering capacity of anaerobic systems.
The nature of the wastes to be added as co-substrates to anaerobic digesters is therefore something that must be thoroughly studied
Similar Juice mix with supplemental ammonia did not show failure
Variability in the nature of the HSW must be monitored as sudden changes in the HSW feed might push digesters to failure

41. Biomethane Potential Analysis
Black & Veatch | November 2015
Biomethane Potential Analysis

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April 29, 2014