Grease Digestion for Renewable Energy, Sustainability, and

E i t l E h tEnvironmental Enhancement

New England Interstate Water P ll ti C t l C i i

PRESENTATION

Pollution Control Commission

Co-authors

PRESENTATIONOctober 7, 2008

Perry Schafer, PE Brown and CaldwellDon Trueblood, Brown and CaldwellKen Fonda, PE, Brown and Caldwell

Craig Lekven, PE, Brown and CaldwellJonathan Keaney, PEBrown and Caldwell

Grease Problems are Frequent –in Wet Wells and Other Places

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Goals of FOG Digestion

Provide long term sustainable means of disposalMaintain or improve current operationsGenerate beneficial resources

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Anaerobic Digestion Background

Biological ProcessReduces total solids, generates biogasCan generate class A or B biosolid per 503 regsCommon Biosolids Stabilization Process Worldwide–Limited installations in New England

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Benefits of Digestion of Fog

Digestion occurs at elevated temperatures that assist in homoginizing FOGassist in homoginizing FOGFOG would represent a small relative volume for most digestion operationsmost digestion operationsLow energy processIncreases production of BiogasIncreases production of Biogas

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Anaerobic Digestion and Sustainability

Sustainability of DigestionN t d ti f lid–Net reduction of solids

–Low energy requirements Shared construction and operating costs–Shared construction and operating costs

–Maximal beneficial reuse of waste materialsCogeneration of biogasCogeneration of biogas Potential for beneficial reuse of biosolids

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Drivers for “Grease to Energy”

Minimize sewer problems – blockages and odorsObtain renewable fuel and energy value of grease resourcesReduce greenhouse gas emissions and air pollutantsA hi i b fitAchieve economic benefitsBe Green and Sustainable

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Yellow Grease

Brown Grease

Characteristics of Brown Grease

% solids <1 to >15%BOD 10,000 to

130,000 mg/LpH Acidic (4 to 5)VS/TS 90 to 97 %VS reduction 80 to 90 %in digestionC/N ratio High

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Digester Loading Rates for Brown Grease

Consistent loading (no slugs) Warmed grease(no slugs)Research shows good stability up to ~30%

Warmed grease frequently 1 to 30% of VS load to digester

Over 30 to 50 % grease load, more susceptible to upsetsupsetsLimited experience at 100% grease loadingg g

Wastewater sludges ( / i )

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(manure/organics)

Proper Mixing is Crucial

Prevent surface mat!Disperse incoming LCFAsInsure consistent temperature

Significant surface turbulence required

Surface withdrawal

Various Mixing

Systems

Surface withdrawal

E S b d C

y

C ti l Fi d Fl ti C

WithdrawalWithdrawal

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Egg or Submerged Cover Conventional Fixed or Floating Cover

Theoretical Methane Content of Biogas

Chemical Methane, Substrate Composition % of Total Gas

Fat C15H31COOH 72

Protein C H ON 63Protein C4H6ON 63

Carbohydrate C6H12O6 50

From Jewell & McCarty work in 1960s and 1970s

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Assumptions for Example Calculations

Sludge GreaseSludge GreaseTS = 5% TS = 10%

VS 78% VS 95%VS = 78% VS = 95%VSR = 55% VSR = 85%

Bi Bi16 ft3 20 ft3Biogas = Biogas =

Methane = 64% Methane = 72%

16 ftlb VSR

20 ftlb VSR

Methane = 64% Methane = 72%

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Example with Standard Assumptions (add 25 % grease solids load)

Sludge Sludge %Sludge Sludge %only + grease increase

Gallons fed 23,500 gpd 26,500 gpd 12.5

TS fed 10,000 lbs/d 12,500 lbs/d 25

VS fed 7,800 lbs/d 10,175 lbs/d 30

VS destroyed 4,290 lbs/d 6,310 lbs/d 47

Biogas 68,600 ft3/d 109,000 ft3/d 59

Methane 43,900 ft3/d 72,500 ft3/d 65

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Example with Symbiotic Assumptions(same 25 % grease solids load)

Sludge Sludge %g gonly + grease increase

Gallons fed 23,500 gpd 26,500 gpd 12.5

TS fed 10,000 lbs/d 12,500 lbs/d 25

VS fed 7,800 lbs/d 10,175 lbs/d 307 210 lb /d 68

VS destroyed 4,290 lbs/d 6,310 lbs/d 47

Biogas 68,600 ft3/d 109,000 ft3/d 59

7,210 lbs/d 68123,900 ft3/d 81

f 3/Methane 43,900 ft3/d 72,500 ft3/d 65

82,400 ft3/d 88

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Sludge VSR 55 → 65% Grease VSR 85 → 90%

Potential Reasons for this Symbiotic Response

1. Greater level of biological activity within the digesting massdigesting mass

2. Trace metal deficiency (without grease)3 Trace metal stimulation (with grease)3. Trace metal stimulation (with grease)4. Improved C/N ratio with grease (ww sludge

can have low C/N ratio).can have low C/N ratio).

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Key considerations for implementation

Determination of ideal loading rate and biomethane potential (BMP)potential (BMP)Determination of toxicity

Too high a dose can have detrimental impact–Too high a dose can have detrimental impactConsideration of other digestion supplementsD t i ti f t i t d fi iDetermination of nutrient deficiency

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Summary

1. Limiting grease discharges to sewers –well-recognized approachwell-recognized approach.

2. Disposing grease to landfills creates problems including GHG emissions.p g

3. Grease wastes are valuable feedstocks for renewable energy – economically viable

j t b i i l t dprojects are being implemented.4. Indications of symbiotic activities when

co-digesting sludges and greaseco-digesting sludges and grease.

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