A Green House Gas Balance for Compost

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A Green House Gas Balance for Compost

• Sally Brown
• University of Washington

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Global Warming Basics

• Everyday the sun heats the earth
• Every night much of this heat leaves the earths
  atmosphere and we cool down

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While this has been happening since weve 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

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Different gasses that trap heat
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(No Transcript)
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Major culprits

• Fossil fuels
• Cars
• Power plants

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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

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Landfill-Lagoon feedstocksShort term carbon cycle
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Short term carbon cycle is too fastand is not
considered in GHG accounting except
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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

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Options

• Landfill gas capture
• Anaerobic digestion
• Direct land application
• Composting

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A Greenhouse Gas Balance for Composting
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How it worksBasic Rules

• You make a difference by stopping gasses from
  being released
• Or by putting carbon back into storage

Federal Reserve Bank
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In Greenhouse Gas Parlance

• Avoidance- stopping gasses from being released
• Sequestration- putting carbon back into storage

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Two Accounting Firms

• CA regulations
• Protocols being developed
• Well intentioned, political process
• Chicago Climate Exchange-
• Voluntary exchange where carbon credits are
  bought and sold

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For accounting purposesCredits 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, doesnt 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

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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

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Feedstocks-Methane generation potential

• Food waste- 12 Mg CO2equiv per Mg food waste

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Yard Waste-Methane generation potential

• Grass clippings
• 5.5 Mg CO2equiv per Mg
• Leaves
• 1.2 Mg CO2equiv per Mg

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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

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Caveats

• 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

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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

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Windrow

• When a pile goes anaerobic-
• Odor will be first indication of anaerobic
  conditions
• In addition to odoriferous compounds
• CH4
• N2O

PhotoCogger, WSU
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Formation

• 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

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Methane and Nitrous Oxide in a Compost Pile
Hao et al., 2001
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Methane and Nitrous Release
Release can occur from pile surface as well
as when the pile is being turned
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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

http//www.ipic.iastate.edu/
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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

http//www.ipic.iastate.edu/
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Release can be controlled
Mixing high C amendments like straw into wetter
feedstocks is a way to prevent release of GHGs
http//score.rims.k12.ca.us/activity/experimentalf
arm/sfarm.htm
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Then you have the compost

• Potential for carbon credits for using compost

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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

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Recycled Organics Unit(http//www.recycledorganic
s.com/publications/reports/)

• Benefits with reduced water use, fertilizer
  value, and reduced herbicide use
• Avoidance credits

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To Conclude

• Potential to get GHG credits from compost both
  from avoidance and from sequestration

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To Conclude

• Avoidance credits are larger- primarily from
  methane avoidance from feedstocks
• Sequestration- from replenishing soil OM

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To Conclude

• Debits as well
• These primarily from GHG emissions during
  composting, transport to and from site also can
  figure in