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

QUESTIONS?

Melissa Pennington EPA Region 3215.814.3372

pennington.melissa@epa.gov