MANAGING PLASTIC WASTE - Plastics and Environmental Sustainability - page 399

Table 9.5 Environmental Features of Plastic Waste Management
Options

Process GHG

emission

Waste Toxic

emissions

Product

Pyrolysis Very low ~15-20% char,

silica, ash

Very low Oil/gas

Gasification Very low Char/tar Very low Syngas

Anaerobic
digestion

Very low Residue Very low Fuel gas

Incineration High Char/residue Temperature

dependent

Energy

Chemolysis Very low Residue Low Chemicals

Compostin g a High Residue Moderate Compost

Landfillin g b CH 4 gas c Solid Moderate Fuel gas

a Only the biodegradable plastic can be composted and the features are common to
biodegradation as well.
b A modern landfill or an anaerobic digestion facility where all or some of the
methane is collected.

c Anaerobic digestion yields methane in place of CO 2 , and the gas has more than 20
times the global warming potential compared to CO 2 .

9.2.4 Feedstock Recycling

Feedstock recycling is the recovery of monomers (or other chemical raw
material) through depolymerization or other chemical reaction. The
recovery role played by feedstock recycling is illustrated in Figure 9.7 .
Controlled “cracking” (Paszun and Spychaj, 1997) of the waste breaks down
the long-chain molecular structure of the plastic yielding shorter chains and
smaller organic molecules. These might be used as feedstock in chemical
processes including resin synthesis. This pathway of waste plastic to virgin
resin is particularly attractive from a sustainability standpoint even though
some losses are inevitable in the process. Both Nylon 6 and PET waste
are recoverable efficiently using this approach. Depending on the chemistry
used, feedstock recovery might be via hydrolysis, glycolysis,