Page 271 - Materials Chemistry, Second Edition

LIFE CYCLE ASSESSMENT AND END OF LIFE 259

Where a material is recovered and recycled, the resource and energy
consumption and environmental releases associated with the manufacture of
a new product are typically calculated and included in the LCA. Recycling
can be closed- or open-loop in nature. In closed-loop recycling, the recovered
material (e.g., aluminum can) is recycled back into the same product (i.e., alu-
minum can). In open-loop recycling, the recovered material (e.g., newsprint)
is recycled into a different product (e.g., tissue paper). In either case, these
parameters were compared against parameters for manufacturing the product
using virgin resources to estimate net resource and energy consumption and
environmental releases. This procedure is also applied to energy recovery from
processes, such as WTE or landfill gas-to-energy, as well as to compost product
application.
Another system boundary decision is where waste treatment and disposal
end. Where liquid wastes are generated and require treatment (usually in a
publicly owned treatment works), the resource and energy consumption and
environmental releases associated with the treatment process are included.
For example, if biological oxygen demand (BOD) from an anaerobic digestion
facility is treated in an aerobic biological wastewater treatment facility, then
energy is consumed to supply adequate oxygen for waste treatment. Likewise,
if a solid waste is produced that requires burial, energy is consumed in the
transport of that waste to a landfill during its burial (for example, bulldozer)
and after its burial (for example, gas collection and leachate treatment systems)
in the landfill. Also, where compost was applied to the land, volatile organic
chemical (VOC) and nitrous oxide (N 20) emissions should be considered for
inclusion in the LCA.
A noted controversial area is carbon storage. There is potential long-term
carbon storage associated with the following aspects:

• Non-degraded organic fraction remaining in landfills.
• Application of compost product to soils and subsequent
improvement in soil carbon.
• Recycling of paper and subsequent changes in timber harvesting
that leaves trees standing longer and sequestering more carbon
than they otherwise would.

11.4.4 Geographic Boundaries
Geographic boundaries for an LCA of waste management are typically tied
to the community, city, or region in which waste is generated. They are also
tied to where the wastes are managed, which can be within the region of gen-
eration or outside of the region of generation (e.g., long haul transfer and
disposal in an out-of-state landfill). Up- and down-stream from the location
of the waste management facilities are the energy and materials production
processes.
Another geographic boundary issue is related to the disposition of recycled
(or secondary) materials. In many regions, a large percentage of the recovered