Page 77 - Materials Chemistry, Second Edition

Life Cycle Assessment: Principles, Practice and Prospects
64
Table 6.4 Technology descriptions and key assumptions for the study
Technology Key assumptions Description of process
Landfill of Values for methane generation from Involves direct dumping of material into
MSW organic fractions were taken from clay-lined (or synthetically lined) cells
Smith et al. (2001). Assume landfill where waste is compacted and covered
gas capture is in place in landfills, on a daily basis with dirt. Pipes for
accounting for 80% of overall collecting gas and leachate from the
methane generated/emitted from landfill are built into the waste piles as
landfills. Of this 80%, assume 55% of they are constructed. Collected gas may
methane is captured. Of this 55%, be flared or used for energy production.
75% results in electricity production
and the remaining 25% is flared. Of
the remaining 45% not captured,
assume 10% degrades through the
landfill cap. CO is also sequestered in
2
the landfill.
Composting Recovery rates at kerbside are 90% for Involves shredding green and food
green waste green waste, and 35% for other waste, placing in piles or windrows
organics (non-food). 60-70% of input (with partial forced aeration when food
to process becomes compost output waste is present), turning and refining.
Benefits are achieved with application
Composting Recovery rates at kerbside are 65% for
green and food 90% for green waste, and 35% of the compost product to land.
food waste for other organics; 45-55% of input to
process is compost output
Anaerobic Digestion is followed by aerobic Involves processing organic material in
digestion of compost production. Recovery rates at a digester (i.e. in the absence of air),
green and kerbside are 65% for food, 90% for generation of biogas that is converted
food waste green waste and 35% for other to electricity, and composting of
organics; 30–50% of input to process digester output A
is compost output; 80–100 kWh/t net
electricity output.
Aerobic 60-70% of input to process is output. Involves particle size reduction,
stabilisation Of this output, 34% is compost and homogenisation, composting to reduce
of MSW 66% is stabilised residue sent to putrescible substances, landfilling of
landfill. Automated ferrous metal stabilised material (which reduces
recovery. volume and emission potential),
recovery of metals and recovery of
organic material as compost
Anaerobic 55-65% of input to process is output. Involves particle size reduction,
digestion of Of this output, 28% is low-grade homogenisation, processing of organic
MSW compost and 72% is stabilised residue material in a digester, generation of
sent to landfill. Automated ferrous biogas which is converted to electricity,
metal recovery; 0-20 kWh/t input net composting of digester output,
electricity output. landfilling of stabilised material,
recovery of metals and recovery of
some organic material as compost
Gasification/ Output is 30% of input. Of this A term that covers a range of new (or
pyrolysis of output, 65% is grit/slag, 30% is inert ‘advanced’) thermal waste treatment
MSW filling and 5% is residue from flue gas processes. The initial stages occur under
cleaning. Automated ferrous metal restricted air (oxygen) supply, and the
recovery, and some plastics recovery; actual combustion of generated gas or
400-450 kWh/t net electricity oil (for energy recovery) occurs at a
generation, no steam. subsequent stage. The output is
electricity, grit, slag, fly ash and some
recyclable materials depending on the
specific technology.

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