Environmental Engineering Reference
In-Depth Information
or feed) that are composed in whole, or in significant part, of biological products,
renewable agricultural materials (including plant, animal and marine materials) or
forestry materials, and includes biobased intermediate ingredients or feedstocks.
The USDA then goes further to establish minimum biobased content standards for
a whole range of product categories. In order to be listed, a product or package
must meet or exceed the minimum biobased content percentage in its given
category in order to use the
Certified Biobased Product
label. Where minimum
biobased content standards for a product category have not been established,
companies may apply for the Certified Biobased Product label if the product
contains a minimum of 25% biobased content.
The emerging biobased manufacturing industry is producing products that
include materials containing mixtures of both biobased and petroleum-derived
components. For example, PET is one of the most commonly sold plastics
worldwide, most commonly recognised as food packaging PET bottles. PET is a
polyester produced by the polymerisation of a diol (ethylene glycol) and a diacid
(terephthalic acid). While both monomers can be produced from biological
fermentation, the former is much easier than the latter. Currently, most PET is a
combination of bio- and fossil-derived monomers, and such materials can be
classed as biobased. In some cases PET will be 100% biobased showing that, even
within the same material, the biobased content can vary; such differences may
need to be clarified to maintain customer assurance.
This issue is also important where refuse-derived wastes are combusted, where
CO
2
of both fossil and biological carbon is released and, through gasification and
fermentation technologies, can be converted into ethanol for use as a fuel or
feedstock for PE or other material manufacture. In this case there is no technical
difference in the product but, if a premium is demanded for biobased materials,
the consumer needs assurance that the product they purchase can at least be
'deemed' to be of biological origin (though assurance procedures).
There are two approaches to determine the biobased content of a material or
product: through either carbon isotope analysis or based on mass calculations.
The pros and cons of each approach are discussed in the following sections.
8.6.1.1
Carbon Isotope Ratio Analysis
The Earth's atmosphere contains isotopes of carbon including the main stable
isotope
12
C and an unstable isotope
14
C with a half-life of around 5,730 years.
These are present in a relatively constant proportion. Plants absorb both forms as
carbon dioxide during photosynthesis. When an organism dies, the
14
C in the
residue decays over time. In the resulting fossil coal, oil and gas deposits, which
are millions of years old, there is no
14
C. The measurement of the ratio of
12
C:
14
C
in a product in comparison to reference atmospheric ratios can be used to provide
an estimate of the proportions of fossil and biogenically derived carbon in a
product or material.
