Environmental Engineering Reference
In-Depth Information
Biodegradable plastics are not a significant fraction of the MSW stream
as yet. If they were indeed present in the waste and were anaerobically
degradable, these too will be converted into biogas. Some bio-based
polymers such as PLA, PHA, and others are promoted for packaging use
as “compostable” plastics. Composting is an accelerated biodegradation
process that converts waste into carbon dioxide and compost substrate.
Complete mineralization of polymers in the waste, however, do not leave a
recalcitrant humic residue and therefore do not contribute to the compost
product, and are not suitable substrates for composting. There are useful
applications for compostable plastics as in the case of compostable plastic
yard waste bags that can be filled and composted conveniently without the
need to remove the plastic bag from the waste stream. With some packaged
foods, where plastic packaging is intimately associated with contents and is
disposed along with food waste for composting, there is some justification
for using compostable plastics. The quality of compost produced in these
cases will be superior with no plastics residue in the product. This
advantage, however, must be balanced with the risk of compostable plastics
inadvertently contaminating a recycling stream.
9.3 SUSTAINABLE WASTE MANAGEMENT CHOICES
Post-use products often have a considerable service life, resource value,
and extractible energy associated with them. Significant nonrenewable
resources were used in their production by processes with adverse
environmental externalities. Majority of post-use plastics in the US waste
stream unfortunately end up in landfills. Disposal in landfills ranks low
from a sustainability standpoint because of gas emissions, leachate, and
waste of the valuable plastics resources. Waste plastic do not generate gas
nor leachate in landfills. Only uncontrolled backyard burning (burn barrels)
is worse than landfilling, as it emits particulates, air pollutants, and
particulates creating a health hazard. Where any PVC is in the burnt waste,
(PAHs), a known carcinogen, are released into the air. Incineration of waste
is closely controlled and modern plants do not release significant levels of
dioxins.
Desirable waste management options must minimize three footprints that
materials, and minimize pollution.
