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Introduction to Anaerobic Digestion
for Wasted FoodMelissa Pennington
US EPA Region 3
Reducing Wasted Food is Important
Goal: Cut Food Waste in half by 2030
Where is all the Wasted Food going to go?
Food Diversion Success
INCREASED COMPOSTING
& AD CAPACITY NEEDED
Capacity Building FocusComposting Anaerobic Digestion
Environmental Benefits of Anaerobic Digestion
u Diversion of organic wastes from landfills
u Methane emissions reduction
u Production of renewable energy
u Soil improvement opportunities
u Nutrient management alternatives
Anaerobic Digestion is “Digestion”
Food and water go in
Bacteria go to work
Energy, solids, and liquids come out
Anaerobic Digestion Basics
uHappens in a sealed container or vessel uNo OxygenuMicroorganisms break down organic
material uHeat is generateduBiogas (Energy)uDigestate (Solids and Liquids)
AD Feedstocks
uWasted Food uAnimal manures
uFats, oils, and greases (FOG)uSewage sludge/wastewater
uYard waste/Crop residuals (Dry Digesters) uOther high strength wastes
Biogas = a mixture of approximately 60% methane (CH4) and 40% carbon dioxide (CO2) together with trace levels of other gases and water vapor
• Odorless • Colorless• Low explosive potential
How is Biogas Used?uBurned to produce heat uCHP to generate
electricity and heatuCompressed for vehicle
fueluAdded to natural gas
pipelinesuProduce biodegradable
plastics
What do you do with Digestate?
SOLID
u Soil amendment
u Animal bedding
u Alternative daily cover at landfills
LIQUID
u Liquid Fertilizer
u Discharge to POTW
Digesters that Process Wasted Food
u Digesters designed primarily for wasted food§ Feedstocks from a variety of sources § Dedicated industry units
u On-Farm Digesters
u Digesters at Water Resource Recovery Facilities (WRRFs)
Basic Types of AD Systems
u Wet Digesters Ø Low SolidsØPumpable
u Dry Digesters ØHigh SolidsØ StackableØAKA Dry Fermentation
u Batch Systemu Continuous Flow
Dry Fermentation Digestersu Feedstocks can include:
Ø Wasted Food
Ø Yard Waste
Ø Agricultural (animal bedding and crop residue)
u No mechanical mixing
u No liquid added
u No liquid digestate
University of WisconsinOsh Kosh Dry Digester