Environmental Engineering Reference
In-Depth Information
The recycling process can be either closed loop or open loop: in closed
loop, recycling the plastic waste is recycled into the same product it was
derived from, such as in bottle-to-bottle recycling. Generally, a fraction of
therecycledresinismixedinwithvirginresininthefabrication ofproducts.
In the United States, some PET bottles presently have up to 50% of recycled
down cycling), the recycled plastic is used to replace at least a part of the
virgin resin used to manufacture a different product; PET bottles are
predominantly (72% in 2007) (Li Shen and Patel, 2010) recycled into fiber
and only 10% in bottle-to-bottle conversions.
Based on a meta-analysis of LCA studies (Waste & Resources Action
Program, 2006), the environmental impact of recycling was found to be
much lower (by about 50%) compared to incineration or landfilling of
plastics as long as the recycled resin can be substituted for at least
approximately 33% of the virgin material. This ratio represented a
break-even point where recycling and incineration have about the same
overall impact. But, the meta-study also found incineration to be preferred
over recycling where substantial washing and cleaning costs were involved
prior to recycling. The specific impact categories used in the assessment
were energy use, resource consumption, GHG emissions, waste generation,
toxicity, and other energy-related impacts such as acidification or
eutrophication.
The energy costs, GHG emissions, and other emissions are generally lower
for manufacturing products using recycled resin as opposed to virgin resin
of the same type. This “avoided energy, resource consumption, and
emissions” (see
Fig. 9.11
) represent the main benefit of recycling. Savings
in energy and GHG emissions vary with the type of resin (and the specific
LCA used to calculate these). Recycling resin primarily saves the feedstock
extraction and resin manufacturing energy, but adjusted down bya material
loss factor inherent to the process. As the feed-stock related energy costs
are avoided, a recent study found producing recycled PET pellets to takes
onlyabout 15% oftheenergy demand associated with producing virgin resin
pellets (Franklin Associates, 2011); the comparable estimate for HDPE is
approximately12%.TheestimatedavoidedcarbonvaluesforproducingPET
and HDPE pellets compared to virgin resin pellet production was estimated
to be 71% and 75% respectively. These are large differences and the energy,
