I’m currently finalizing a life cycle analysis (LCA) of
wood waste management alternatives for Seattle Public Utilities. We are
waiting on the latest update of EPA’s TRACI (Tool for the Reduction and
Assessment of Chemical and other environmental Impacts) model which we plan to use
to aggregate toxic and carcinogenic air pollutant emissions into toluene,
benzene and 2,4-D equivalents. This aggregation is like the aggregation
that is done to add together carbon dioxide, methane, nitrous oxide, CFC and
other greenhouse gas emissions into carbon or carbon dioxide equivalents.
Based on the previous version of TRACI weights, combusting
wood waste to replace natural gas reduced greenhouse gases, but increased toxics
and carcinogens, versus landfilling the wood waste. The same was true for
coal, although the differences were much smaller than for natural gas, so that
comparison could go either way with the updated TRACI weights. These
comparisons were for the combustion of wood waste, natural gas, or coal in
industrial boilers. The latest TRACI update apparently will be based on
the United Nations Environmental Program (UNEP) and Society of Environmental Toxicologists
and Chemists (SETAC) harmonization model for the impacts of chemical releases
to the environment. But we have to wait for EPA’s peer review of
the update before that update will be available.
I also have done the comparison for yard debris composting
versus WTE incineration. There the comparison favors yard debris
composting, due to the upstream benefits from carbon sequestration and reduced
synthetic fertilizer and pesticides usage as a result of building healthier
soils from adding composts. Composting of clean wood waste (i.e.,
non-painted, non-treated) would yield the same result. (Several months
ago I circulated an Excel-based model to interested GreenYes subscribers that
shows these results.)
For the landfilling with landfill gas collection and use to
generate electricity versus WTE incineration, the result favors landfilling
wood waste and yard debris due to the carbon sequestration in the landfill of materials
that are slow to decompose, such as wood waste and tree and plant prunings.
We expect to have the LCA for wood waste management alternatives
completed early next year. So stay tuned for that one.
Regards,
Jeffrey Morris, Ph.D.-Economics
Sound Resource Management
2217 60th Lane NW
Olympia, WA 98502-0903
360-867-1033
360-319-2391 mobile
jeff.morris@no.address
www.zerowaste.com