Page 276 - Materials Chemistry, Second Edition

264 LIFE CYCLE ASSESSMENT HANDBOOK

• The environmental benefits of recycling are highly dependent
on the type and amount of material substituted by the recycla-
bles. For example, recycling performs better when it is assumed
that recycled material replaces an equivalent amount of virgin
material.
• The difference in environmental impact between WTE and recy-
cling decreases as higher waste-to-energy recovery efficiencies
are assumed and the energy generated replaces electricity and
heat from fossil fuels instead of non-fossil fuels. In general, WTE
facilities which produce combined electricity and heat perform
better than those that only produce electricity or heat.

In our experience in conducting LCAs for waste management, we typically
will focus on the assumptions listed in Table 11.4 as key drivers for results.

Table 11.4 Key assumptions that can significantly impact results of an LCA for waste.
Activity/Process Key Assumptions

Recycling • Amount of readily recyclable materials in the waste stream
• Participation factor (the proportion of the service region
that participates in recycling)
• Capture rate (the proportion of recyclables generate that are
placed in recycling collection containers vs trash containers)
• MRF separation efficiency
• Final destination for recovered materials (domestic vs
foreign markets)
Composting • Amount of readily available (e.g., easily separated) organic
material in the waste stream
• Participation factor (the proportion of the service region
that participates in formal and backyard composting)
• Potential for offset of other products (fertilizer, etc.)
• Soil carbon storage
Waste-to-Energy • BTU value of input waste stream
• Plant heat rate (a measure of energy conversion efficiency)
• Mix of fuels offset in the utility sector by virtue of electrical
energy displacement
• Type and amount of metals recovered for recycling

Landfill • Landfill gas production parameters including methane
yield and decay rate
• Landfill gas collection efficiency
• Methane oxidation rate
• Mix of fuels offset in the utility sector by virtue of electrical
energy displacement (if an energy recovery system is in
use)