Page 81 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 63

decompose in landfills, but this is subject to landfill conditions (e.g., tempera-
ture, moisture, presence of microbes). It may take many years for the decom-
position to occur, and the decomposition may never completely convert all the
carbon content to carbon dioxide and methane. Samples of newspaper and
other bio-derived products excavated from actual landfills have shown very
little degradation [11]. Landfill simulation studies have also indicated that the
lignin content of products derived from woody biomass tends not to decom-
pose [12]. Biomass decomposition can also be inhibited by moisture-resistant
coatings, fillers and additives, or sandwiching biomass layers between layers
of foil or plastic.
If landfilled biomass does decompose anaerobically, there are different pos-
sible fates for the methane that is generated. If the methane escapes into the
atmosphere uncaptured and untreated, it results in additional global warming
potential. If the methane is captured and flared (with or without energy recov-
ery) or oxidizes as it travels through the landfill cover, then the carbon content
returns to the atmosphere as carbon-neutral CO r If the captured methane is
burned with energy recovery, then the useful energy recovered can displace
natural gas or electricity consumption, and credit should be given for the dis-
placed energy and emissions.
Because of the many uncertainties surrounding biomass decomposition in
landfills, it is advisable to conduct sensitivity analyses on the carbon storage
and releases associated with landfilled biomass products.
Similar carbon tracking issues apply to waste-to-energy combustion of mate-
rials. Carbon dioxide from combustion of biomass-derived material is consid-
ered carbon neutral, while carbon dioxide from the combustion of materials
derived from fossil fuels is considered as a net contribution to global warm-
ing potential. Regardless of whether the carbon in the combusted material is
biogenic or fossil carbon, credit should be given for the energy and emissions
displaced by energy recovered from combustion of the material.

3·5 Evolution of LCA Practice and Associated Issues

In recent years, LCA practice has evolved rapidly, from a specialty field
practiced by a handful of practitioners with closely guarded databases, to a
widely used tool with emphasis on transparency and sharing of data. Life
cycle inventory data are publicly available at various levels of detail in inter-
national databases, national databases, and from industry associations. A
few examples of publicly available life cycle inventory databases include
the European Commission ELCD database, the U.S. LCI database, and plas-
tic resin databases published by European and U.S. plastics industry asso-
ciations [13,14,15,16]. Although LCA practice still requires a high degree of
expertise and knowledge, the availability of sophisticated LCA software
such as SimaPro and GaBi have made LCA accessible to a much wider user
base [17,18].