november 2015 blair wisdom co-digestion – the path to success

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BLAIR WISDOM

CO-DIGESTION – THE PATH TO SUCCESS

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AGENDA CO-DIGESTION OVERVIEW FEASIBILITY ENSURE SUCCESS OF RECEIVING STATIONS

AND PRETREATMENT SAFEGUARD FOR STABLE DIGESTER

PERFORMANCE

CO-DIGESTION OVERVIEW

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• 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

WHAT IS CO-DIGESTION?

Black & Veatch | November 2015

• 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

WHY WOULD YOU CO-DIGEST?


Energy

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ORGANIC RESOURCES-TO-ENERGYCO-LOCATION/(CO)-DIGESTION AND GAS UTILIZATION

GAS UPGRADING

RNG

FLEET

PIPELINE

Sludge

WWTP

EXISTING DIGESTERS

CO-GEN GRID

COMMERCIAL ORGANICS

SOURCE SEPARATEDORGANICS/

ORGANIG FRACTION OF MSW

FOG

DEDICATEDDIGESTERS


• Reliable systems provide valuable service to industries

• Increased revenue

• On-site power production provides greater reliability

• Flexibility for multiple energy uses

CO-DIGESTION CAN ENHANCE OVERALL SUSTAINABILITY


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PROS/CONS OF CO-DIGESTION

Black & Veatch | 2 September 2015

Source: Braun, Wellinger (2003); Grasmug, Braun (2003); Schmelz (2007); STOWA, (2006) adapted

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

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PROS/CONS OF CO-DIGESTION

Black & Veatch | 2 September 2015

Source: Braun, Wellinger (2003); Grasmug, Braun (2003); Schmelz (2007); STOWA, (2006) adapted

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

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FEASIBILITY

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PROCESS CAPACITY

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• Drivers: • Combat rising energy costs• Institute sustainable practices• Fully utilize equipment capacities

• Capacity evaluation:• Average 32 day SRT• 100 ppd of VS/kcf

ROCK RIVER WATER RECLAMATION DISTRICT


ROCK RIVER EXISTING STABILIZATION AND GAS HANDLING

Excess Digester Capacity Excess Gas Treatment Capacity

Excess Engine Generator Capacity

Limited Gas Handling Capacity


AVAILABILITY OF HSW

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SIGNIFICANT BIOGAS POTENTIAL IN HIGH STRENGTH WASTES

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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)


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


• 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

INCREASED COMPETITION FOR FOG – LONG TERM OUTLOOK?

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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, andresidents of organics collection

COMMERCIAL AND RESIDENTIAL SOURCE SEPARATED ORGANICS - CO-DIGESTION

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http://www.jepsonprairieorganics.com/compostprocess/img2.jpg

http://www.jepsonprairieorganics.com/compostprocess/img4.jpg

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


ASSESS THE BENEFITS

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Operational Costs• Some added maintenance• Added loads to the plant• Potentially added biosolids

disposal costs

B&V - 22

WHAT ARE THE OPERATIONAL COSTS AND BENEFITS?

Operational Benefits• Increased biogas• Increased waste heat from

engine generators• Tipping fees• Service to customers


ENSURE SUCCESS OF RECEIVING STATIONS AND PRETREATMENT

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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


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


DEBRIS IN HAULED WASTES


FOG/BG CO-DIGESTION EXAMPLE: WATSONVILLE WWTP

Source: Kester, G. (2008)

PLANT DESIGN CAPACITY: 12 MGDFOG CO-DIGESTION: 3,000 – 10,000 GAL/DAY

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EXAMPLE – DES MOINES WRA - 170,000 GALLON RECEIVING TANK

Black & Veatch November 2015

DES MOINES WRA - RECEIVING/STORAGE TANK

• Mixed via recirculation pumps and nozzles

• Lined for corrosion control


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?


SAFEGUARD FOR STABLE DIGESTER PERFORMANCE

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OPEQUON WRF – FREDERICK WINCHESTER SERVICE AUTHORITY (FWSA)

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• Current Solids Treatment:• Lime-Stabilized biosolids – landfill

disposal• Frame and Plate Filter Presses

• Design Solids Process:• Two mesophilic primary digesters

and one secondary digester

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SOLIDS PROCESS 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, daysMaximum Month

Annual Average

1520

VS Loading Rate, ppd/kcfMaximum Month

Annual Average

154132

Expected Volatile Solids Reduction, %Maximum Month

Average Annual

4545


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


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


Waste Characteristics (Part II)

High Strength Waste Total COD(mg/L)

TS(mg/L)

VS(mg/L)

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.


• 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


• 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

Failure Caused by Shock Load to Digester

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



0 2 4 6 8 10 120

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50

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Control 8% DAF 12% DAF 16% DAF20% DAF 25% DAF 5% GTW 9% GTW12% GTW 16% GTW 22% GTW 16% GTW (Diluted)22% GTW (Diluted)

Time in days

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L)Biomethane Potential Analysis

Page - 3 April 29, 2014

november 2015 blair wisdom co-digestion – the path to success

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