113
in the polymer, its glass transition temperature increased, which gives a larger temperature range of operation in the rigid state, but limits their temperature range for
processing and use in a rubbery and flexible state (Zhang et al. 1997).
Once the polyhydroxyalkanoates are disposed into the environment, they will
easily degrade into carbon dioxide and water aerobically by microorganisms (Chee
et al. 2010). The period of degradation will vary according to the environment.
According to the American Society for Testing and Materials (ASTM) standards,
polyhydroxyalkanoates are compostable and biodegradable materials in marine
environments. If disposed into anaerobic sewage, it will take 6–8 months to degrade,
while it will take a few years to degrade in seawater. The presence of UV light
increases the rate of polyhydroxyalkanoates degradation (Verlinden et al. 2007). In
natural aerobic environments, polyhydroxyalkanoates usually degrade after 60 to
75 weeks (Brandl et al. 1990).
5.2 Polyhydroxyalkanoates Production
5.2.1 Current Commercial Products
Polyhydroxyalkanoates production is already in progress, although it is very limited
comprising only 2.4% of global bioplastic production in 2017 (European Bioplastics
2017). The lack of further implementation of polyhydroxyalkanoates production on
a larger scale is due to the high production costs compared to the petrochemical
industry alternatives (Tan et al. 2014). Currently, the cost of polypropylene and
polyethylene ranges from US$0.6 to 0.87 for one pound, while the polyhydroxyalkanoates prices is within US$2.25–2.75 per pound (Kourmentza et al. 2017).
Current industrial polyhydroxyalkanoates production relies on pure culture fermentation, which increases the overall costs due to the need of sterilization (Fradinho
et al. 2013b). Moreover, fermentation processes are costly due their low yield per
substrate, which typically lie in the range of 18–50% (Salehizadeh and van
Loosdrecht 2004). Additional challenges include control of polyhydroxyalkanoates
structure and properties (Dietrich et al. 2017).
There are four major components to the polyhydroxyalkanoates high costs: cost
of substrate used, productivity, yield per substrate, and the recovery method
(Dietrich et al. 2017). Choosing a suitable substrate is an important factor in the
production of polyhydroxyalkanoates as it affects significantly the costs of production and the potential polyhydroxyalkanoates produced. In fact, over 40% of the
polyhydroxyalkanoates production expenses may be related to the raw materials,
and about 70% of this cost is related to the carbon source (Salehizadeh and van
Loosdrecht 2004). There are substrates that are rich in carbon and nutrients and are
associated with growth. There are also substrates rich in carbon only with no nutrients, and those are not associated with growth (Kourmentza et al. 2017). The most
widely used substrates are glucose, fructose, and fatty acids (Dietrich et al. 2017).
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
in the polymer, its glass transition temperature increased, which gives a larger temperature range of operation in the rigid state, but limits their temperature range for
processing and use in a rubbery and flexible state (Zhang et al. 1997).
Once the polyhydroxyalkanoates are disposed into the environment, they will
easily degrade into carbon dioxide and water aerobically by microorganisms (Chee
et al. 2010). The period of degradation will vary according to the environment.
According to the American Society for Testing and Materials (ASTM) standards,
polyhydroxyalkanoates are compostable and biodegradable materials in marine
environments. If disposed into anaerobic sewage, it will take 6–8 months to degrade,
while it will take a few years to degrade in seawater. The presence of UV light
increases the rate of polyhydroxyalkanoates degradation (Verlinden et al. 2007). In
natural aerobic environments, polyhydroxyalkanoates usually degrade after 60 to
75 weeks (Brandl et al. 1990).
5.2 Polyhydroxyalkanoates Production
5.2.1 Current Commercial Products
Polyhydroxyalkanoates production is already in progress, although it is very limited
comprising only 2.4% of global bioplastic production in 2017 (European Bioplastics
2017). The lack of further implementation of polyhydroxyalkanoates production on
a larger scale is due to the high production costs compared to the petrochemical
industry alternatives (Tan et al. 2014). Currently, the cost of polypropylene and
polyethylene ranges from US$0.6 to 0.87 for one pound, while the polyhydroxyalkanoates prices is within US$2.25–2.75 per pound (Kourmentza et al. 2017).
Current industrial polyhydroxyalkanoates production relies on pure culture fermentation, which increases the overall costs due to the need of sterilization (Fradinho
et al. 2013b). Moreover, fermentation processes are costly due their low yield per
substrate, which typically lie in the range of 18–50% (Salehizadeh and van
Loosdrecht 2004). Additional challenges include control of polyhydroxyalkanoates
structure and properties (Dietrich et al. 2017).
There are four major components to the polyhydroxyalkanoates high costs: cost
of substrate used, productivity, yield per substrate, and the recovery method
(Dietrich et al. 2017). Choosing a suitable substrate is an important factor in the
production of polyhydroxyalkanoates as it affects significantly the costs of production and the potential polyhydroxyalkanoates produced. In fact, over 40% of the
polyhydroxyalkanoates production expenses may be related to the raw materials,
and about 70% of this cost is related to the carbon source (Salehizadeh and van
Loosdrecht 2004). There are substrates that are rich in carbon and nutrients and are
associated with growth. There are also substrates rich in carbon only with no nutrients, and those are not associated with growth (Kourmentza et al. 2017). The most
widely used substrates are glucose, fructose, and fatty acids (Dietrich et al. 2017).
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…