Environmental Engineering Reference
In-Depth Information
The energy difference between using all-virgin resin and substituting
x
% of
recycledresin(forvirginresin)infabricatingaproductcanbeapproximated
as follows, assuming
E
F
and
E
D
to be the same in both cases. The transport
energy costs are not included for simplicity (and because it is variable) for
either case.
Usually as
E
P
;
E
R
+
E
C
, recycling plastics almost always results in energy
saving, that is, Δ
E
is positive and large. An exception (see
Chapter 10
) is
small plastics debris in marine litter where
E
C
can be so large that the above
does not hold. An analogous equation can be written for the pollution load
(including carbon emission), Δ
P
associated with the two processes, again
assuming the impact of either resin to be the same in the fabrication and
disposal phases. Nonrenewable material conserved by using the recycled
resin is
x
percent.
From the consumer's vantage point, recycling increases the product
available per unit input of energy and materials. If recycling rate was 100%,
at least in theory, one input load of polymer should continue to yield
products repeatedly, at a highly discounted processing energy cost! In
practice,recyclingdegradestheplastic,andsomelossofmaterialisincurred
at each cycle and minimal externalities are associated with recycling as well.
The Waste and Resources Action Program (WRAP) study (2006) examined
10 LCAs covering 60 scenarios of plastics waste management. It found
recycling to be the generally preferred waste management method with
maximum benefits being incurred when the virgin resin is substituted for
at near 100% levels. In a 2011 study, the energy costs of collecting, sorting,
and reprocessing of plastics waste into recycled resin pellets was calculated
for PET and HDPE. All virgin material production burdens were assigned
to the first use of material and only collection, sorting, reprocessing, and
transportation were assigned to the recycled stream. This is reasonable
assuming that in the absence of the lower-cost recycled resin, more virgin
resin would have to be used. The environmental advantage associated with
recycling is considerable at 100% recycled resin use as reflected in
Table
