Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by numerous
microorganisms as intracellular energy reserves. The metabolic pathway from
these microorganisms can be bioengineered into a variety of plants for making
PHAs. While this new scheme for producing biodegradable polymers is not yet
commercial, it may have the potential for large scale manufacture at very
low cost. There has been significant research done by government, academic
and commercial organizations over the past decade into bioengineering plants
for this purpose. Numerous challenges, both technical and non-technical, are
associated with commercializing this form of biotechnology. One challenge
is to achieve a high level of polymer production in the plant without a decrease
in crop yield. Another is to economically recover the polymer from the plant
biomass. In the case of commercial crop systems such as oilseed crops, it
is important that oil and meal also be recovered from the seed to capture
their commercial value. In addition to the technical challenges of commercializing
this technology, there are also large non-technical barriers. These barriers
are associated with the utilization of agricultural infrastructure for production
of industrial products. Identity preservation of PHA crops needs to be provided
within the infrastructure and could potentially be quite costly. Another barrier
is managing public opinion of biotech crops. These issues could be more important
than the technical issues when considering overall production costs. In this
report, PEP presents process designs and associated cost estimates for the
production of polyhydroxyalkanoates in agricultural crops. The economics are
compared to those for PHA production by E. coli fermentation. Process economics
are also provided for a typical oilseed crushing plant. The general conclusions
are summarized below:
o PHA by E. coli fermentation offers promise as a means to profitably produce
commercial polymer. Increasing the plant capacity and utilizing E. coli as
the fermentation bacteria significantly improve the process economics compared
to those estimated in PEP Report 115C published in 1998.
o PHA from bioengineered crops could potentially be cheaper than fermentation,
but a number of technical and non-technical hurdles must be overcome first.
From both a cost standpoint as well as public acceptance and identity preservation
standpoints, switchgrass is preferred to an oil seed crop for producing PHAs
on a large scale.
