LCA of organic waste management in Denmark

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LCA of organic waste management in Denmark

• Ola Eriksson
• PhD Industrial Ecology
• University of Gävle

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Agenda

• Background
• Task
• Assumptions
• Scenarios
• Results
• Complaints
• Lessons learned

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Background

• The Danish EPA had developed five scenarios for
  future treatment of organic waste in Denmark
  which include an increased biological treatment
  of organic waste
• The scenarios had to be evaluated with respect to
  environmental impact and energy turnover
• With help of the Life Cycle Inventory (quantified
  flows of material, use of resources, energy,
  emissions to air, water and soil) DEPA would be
  able to perform a socio-economic survey and a
  cost-benefit-analysis
• The socio-economic survey would then play a vital
  role in how to change the legislation in this area

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Task

• Use of resources, emissions to air, water and
  soil, use and generation of energy and
  environmental impacts are calculated for
  management of organic household waste in Denmark
• The study was made together with Andras Baky,
  JTI-Swedish Institute of Environmental and
  Agricultural Engineering

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Key assumptions 1(4)

• The waste
• The organic waste has a dry matter content of 30
  .
• Content of Nitrogen and Phosphorus is 7 and 1.3
  
• Collection and transport
• Collection of waste is based on two general
  assumptions the energy fuel consumption is 0.3
  GJ/ ton waste and the energy content in diesel
  oil is 35.6 MJ per l diesel.
• 40 of the waste to anaerobic digestion is
  transported 80 km by truck and trailer and 60
  is transported 20 km by truck
• The waste to composting is transported 20 km by
  truck

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Key assumptions 2(4)

• Biological treatment
• 50 of the waste to anaerobic digestion is
  digested in a mesophile process, 50 in a
  thermophile process. Biogas production is set to
  125 nm3 per ton of waste treated. Of the incoming
  waste 35 is sorted out to incineration
• 50 of the waste to composting is put into
  windrow compost and 50 into reactor compost
• The carbon-nitrogen ratio has been set to 30
  (input of carbon-rich material)
• Of the incoming waste, 15 is sorted out to
  incineration

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Key assumptions 3(4)

• Thermal treatment
• The incineration plant is a CHP plant with 85
  overall efficiency and 0.35 MJ electricity/ MJ
  heat. No flue gas condensation. The NOx-emission
  is 200 mg NO2/ MJ fuel.
• Downstream processes
• Incineration residues, slag, are recycled to 80
  and 20 of the slag amount is disposed of at a
  landfill. The recycling is made outside the
  system and is not accounted for. All ashes are
  landfilled separately.
• Collected biogas is combusted in a gas engine
  with 90 degree of efficiency, where 38 of the
  energy is recovered as electricity and 52 as
  district heating.

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Key assumptions 4(4)

• Downstream processes
• For compost dry spreaders are used in the spring
  and harrowed into soil within one hour after
  spreading.
• For anaerobic sludge liquid spreader is used in
  the spring using a band spreader and harrowed
  into soil within one hour after spreading.
• Compensatory system
• Heat coal combustion, ? 88
• Electric power coal combustion, ? 44
• Fertiliser (Nitrogen, Phosphorus and Potassium)
  is calculated for western European average data.

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Scenarios
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Environmental impact assessment

• Global Warming Potential
• Acidification Potential
• Eutrophication Potential
• Formation of Photochemical Oxidants
• Consumption of Primary Energy Carriers

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Functional units - fertilisers
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Functional units - energy
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Results 1(2)
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Results 2(2)
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Sensitivity analyses

• No recycling of slag from incineration
• Paper bags instead of plastic bags
• Higher biogas production
• Carbon sink
• Power generation from natural gas instead of coal
• Heat generation from natural gas instead of coal

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Complaints 1(4)

• Published in Waste Management World (July/August)
  (International Solid Waste Association )
• They question the use of cost-benefit analysis to
  deal with waste management problems "The goals
  of recycling projects are typically to conserve
  resources for the future and often to conserve
  resources in other countries," they write. "But
  it is precisely these aspects that are neglected
  in the typical welfare-economic analysis.
• Answer Using welfare-economic analysis is the
  choice of DEPA. Maybe methods for valuation of
  resource conservation have to be developed.

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Complaints 2(4)

• They also level a series of specific criticisms
  at the EPA's choice of assumptions and system
  boundaries, all of which suggest the agency
  exaggerated material recycling's environmental
  impacts compared with incineration.
• Answer DEPA decides. To which extent opinions
  from members of the reference group are
  considered is up to DEPA.
• The eutrophication potential of composting is
  significantly over-estimated, they claim,
• Answer Eutrophicating emissions rely upon the
  carbon/nitrogen ratio. Last minute changes wanted
  by MC could not be considered due to time delay.
  Sensitivity analyses presented in my thesis show
  that C/N ratio is not a key parameter.

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Complaints 3(4)

• while nitrogen leaching from use of artificial
  fertilisers is underestimated.
• Answer A question of confidence in data used.
  The soil model was adjusted to the soils in
  Denmark. The model has been validated in earlier
  projects. The model accounts for extra emissions
  due to organic fertilisers compared to
  artificial.
• Long-term effects of landfilling - important
  where organic waste is incinerated - are not
  considered.
• Answer Emissions for remaining time period were
  calculated and presented. DEPA made a choice to
  only use emissions from surveyable time period.

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Complaints 4(4)

• And not all environmental impacts of mineral
  fertiliser use are included.
• Answer That may be true, but these impacts were
  not expressed in a way that they could be
  included in the model calculations.

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Lessons learned

• Geographical distances and language borders made
  the study less swift
• Time consumption for model adjustments were hard
  to estimate
• LCI is much more information than environmental
  impact diagrams which affects scrutinising and
  reporting
• Once again error search is hard to do for large
  quantities of data
• LCA/SFA assessments can be used in decisionmaking
  in cooperation with officials