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A Green House Gas Balance for Compost . Sally Brown University of Washington. Global Warming Basics. Everyday the sun heats the earth Every night much of this heat leaves the earth’s atmosphere and we cool down. While this has been happening since we’ve had an atmosphere.

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a green house gas balance for compost

A Green House Gas Balance for Compost

Sally Brown

University of Washington

global warming basics
Global Warming Basics
  • Everyday the sun heats the earth
  • Every night much of this heat leaves the earth’s atmosphere and we cool down
while this has been happening since we ve had an atmosphere
While this has been happening since we’ve had an atmosphere
  • Some gasses are more efficient than retaining heat than others
  • With global warming the concentration of these gases in the atmosphere is increasing
  • And as a result, the temperature on the surface of the earth and in the oceans increases
major culprits
Major culprits
  • Fossil fuels
    • Cars
    • Power plants
landfill or lagoon
Landfill or Lagoon
  • What you work with (solid waste) falls under a different classification
  • Most material that gets landfilled or stored in lagoons falls under the short term carbon cycle
  • It is expected that this will decompose and release CO2
landfill or lagoon1
Landfill or Lagoon
  • If the material is sent to a landfill or lagoon where it will decompose anaerobically, it has the potential to release CH4 into the atmosphere
  • As CH4 is 23X worse than CO2- all of a sudden these short term organic residuals start to count
  • Landfill gas capture
  • Anaerobic digestion
  • Direct land application
  • Composting
how it works basic rules
How it works:Basic Rules
  • You make a difference by stopping gasses from being released
  • Or by putting carbon back into storage

Federal Reserve Bank

in greenhouse gas parlance
In Greenhouse Gas Parlance
  • Avoidance- stopping gasses from being released
  • Sequestration- putting carbon back into storage
two accounting firms
Two Accounting Firms
  • CA regulations
    • Protocols being developed
    • Well intentioned, political process
  • Chicago Climate Exchange-
    • Voluntary exchange where carbon credits are bought and sold
for accounting purposes credits are conditional
For accounting purposes:Credits are conditional
  • In order for something to qualify for credits, it has to be a new and innovative practice
  • The status quo, even if it is an environmentally beneficial practice, doesn’t count
  • Projects have to be approved
  • If the project is undertaken by a large entity (like the City of San Diego) the project has to be considered as part of a whole GHG accounting
compost accounting divide process into three parts
Compost Accounting-Divide process into three parts
  • What you compost
    • Outside of compost, would feedstocks generate CH4?
  • How you compost
    • Energy use and gas emissions during composting
  • What you do with your compost
    • Use of compost qualify for sequestration or avoidance credits
feedstocks methane generation potential
Feedstocks-Methane generation potential
  • Food waste- 12 Mg CO2equiv per Mg food waste
yard waste methane generation potential
Yard Waste-Methane generation potential
  • Grass clippings
    • 5.5 Mg CO2equiv per Mg
  • Leaves
    • 1.2 Mg CO2equiv per Mg
avoidance credits
Avoidance Credits
  • Compost facility that processes 1000 dry metric tons of waste per year
  • Mix of 33% manure, 33% newsprint and 33% food waste
    • 333 x 2.6 Mg CO2 for hog manure
    • 333 x 3 Mg CO2 for newsprint
    • 333 x 12 Mg CO2 for food waste
  • 5900 Mg CO2- an optimum value for avoidance
  • This is an ideal case- a maximum value for methane avoidance
  • If the landfill does methane capture value will be reduced
  • If the manure is already directly land applied- the value will be reduce….
  • This was done to show potential
composting process
Composting Process
  • When you compost organics there is the potential for GHGs other than CO2 to be released during decomposition
  • These releases will count as debits
  • When a pile goes anaerobic-
  • Odor will be first indication of anaerobic conditions
  • In addition to odoriferous compounds
    • CH4
    • N2O

Photo:Cogger, WSU

  • Methane is formed as microbes break down carbon in environments where O2 is really limiting- very inefficient way to compost
  • N2O is formed primarily as nitrate is transformed into nitrogen gas- will occur in N rich environments with mildly anaerobic conditions

Methane and Nitrous Release

Release can occur from pile surface as well as

when the pile is being turned

potential n 2 o and ch 4 release
Potential N2O and CH4 release
  • 0.7 g of N2O per kg biosolids (Czepiel et al., 1996)
  • 1.9 kg CH4 per Mg OM (Hao et al, 2004)
  • For your 1000 Mg dry that equals
    • 0.233 Mg N2O
    • 0.95 Mg CH4


5900 mg co 2
5900 Mg CO2 -
  • 0.233 Mg N2O = 296 X 0.233
  • 0.95 Mg CH4=23 x 0.95
  • Total 91 Mg CO2
  • You would end up with 5800



Release can be controlled

Mixing high C amendments like

straw into wetter feedstocks is a

way to prevent release of GHGs


then you have the compost
Then you have the compost
  • Potential for carbon credits for using compost
back in the bank compost is stable organic matter
Back in the bankCompost is stable organic matter
  • Compost is 50% organic
  • Assume that 50% of this is stable
  • Credit for carbon equivalent of 25% of dry weight of compost used
recycled organics unit http www recycledorganics com publications reports
Recycled Organics Unit(http://www.recycledorganics.com/publications/reports/)
  • Benefits with reduced water use, fertilizer value, and reduced herbicide use
  • Avoidance credits
to conclude
To Conclude
  • Potential to get GHG credits from compost both from avoidance and from sequestration
to conclude1
To Conclude
  • Avoidance credits are larger- primarily from methane avoidance from feedstocks
  • Sequestration- from replenishing soil OM
to conclude2
To Conclude
  • Debits as well
  • These primarily from GHG emissions during composting, transport to and from site also can figure in