122
polyhydroxyalkanoates accumulation rates (Wang et al. 2017). The effects of dissolved oxygen were different for different volatile fatty acid substrates.
The role of alternating anaerobic and aerobic conditions to promote polyhydroxyalkanoates storage is well known due to its widespread implementation to
drive biological phosphorus removal. In this process, carbon is stored in an anaerobic period when it is readily available and then used in an aerobic period to drive
more efficient cell growth, which in the case of polyphosphate-accumulating organisms is associated with a replenishment of polyphosphates that can be used as an
energy source in the anaerobic phase to convert volatile fatty acids as polyhydroxyalkanoates. This approach is useful in wastewaters rich in nutrients (Saharan
et al. 2014).
Alternating redox conditions have also been shown to alter the monomer composition of the polyhydroxyalkanoates produced. Work conducted by Bengtsson et al.
on a carbon source from a paper mill waste under anaerobic conditions produced
polyhydroxyalkanoates containing hydroxybutyrate, hydroxyvalerate, and poly- 3hydroxy-2-methylvalerate monomers at 6%, 47%, and 47%, respectively, with
glycogen- accumulating organisms as the main microorganism. The same research
group using a similar wastewater under aerobic followed by anaerobic conditions
achieved polyhydroxyalkanoates with similar monomers produced but at different
concentrations with a ratio of 33%, 51%, and 16%, respectively (Bengtsson et al.
2008). In a separate study conducted by Dai et al. to evaluate the impact of acetate
as a substrate on the polyhydroxyalkanoates composition under aerobic conditions,
the polyhydroxyalkanoates produced contained 93% of hydroxybutyrate monomers
and 7% of hydroxyvalerate monomers. However, when the feeding mode was
changed to an aerobic/anaerobic one, the production of hydroxyvalerate monomers
increased to 30%, while the hydroxybutyrate monomers’ production dropped to
70% (Dai et al. 2007). Furthermore, experiments conducted by Amulya et al.
revealed that under microaerophilic environments and glucose as a substrate, the
content of hydroxyvalerate monomers increased to 21% compared to 8% under
aerobic conditions (Amulya et al. 2016).
5.4.3 Effects of Carbon Source and Raw Materials
Effect on Polyhydroxyalkanoates Composition
Many factors influence the final polyhydroxyalkanoates composition including the
type of substrate employed. Diverse monomer production is linked to substrates
containing a variety of volatile fatty acids (Serafim et al. 2008), making complex
industrial wastes an interesting feedstock where fermentation conditions could be
used to control the final polyhydroxyalkanoates product. Additionally, volatile fatty
acids with odd vs even chain lengths were also found to favor the production of
hydroxybutyrate or hydroxyvalerate (Morgan-Sagastume et al. 2015). Acetate is
one of the most popular carbon sources for polyhydroxyalkanoates production and
S. Sali and H. R. Mackey
polyhydroxyalkanoates accumulation rates (Wang et al. 2017). The effects of dissolved oxygen were different for different volatile fatty acid substrates.
The role of alternating anaerobic and aerobic conditions to promote polyhydroxyalkanoates storage is well known due to its widespread implementation to
drive biological phosphorus removal. In this process, carbon is stored in an anaerobic period when it is readily available and then used in an aerobic period to drive
more efficient cell growth, which in the case of polyphosphate-accumulating organisms is associated with a replenishment of polyphosphates that can be used as an
energy source in the anaerobic phase to convert volatile fatty acids as polyhydroxyalkanoates. This approach is useful in wastewaters rich in nutrients (Saharan
et al. 2014).
Alternating redox conditions have also been shown to alter the monomer composition of the polyhydroxyalkanoates produced. Work conducted by Bengtsson et al.
on a carbon source from a paper mill waste under anaerobic conditions produced
polyhydroxyalkanoates containing hydroxybutyrate, hydroxyvalerate, and poly- 3hydroxy-2-methylvalerate monomers at 6%, 47%, and 47%, respectively, with
glycogen- accumulating organisms as the main microorganism. The same research
group using a similar wastewater under aerobic followed by anaerobic conditions
achieved polyhydroxyalkanoates with similar monomers produced but at different
concentrations with a ratio of 33%, 51%, and 16%, respectively (Bengtsson et al.
2008). In a separate study conducted by Dai et al. to evaluate the impact of acetate
as a substrate on the polyhydroxyalkanoates composition under aerobic conditions,
the polyhydroxyalkanoates produced contained 93% of hydroxybutyrate monomers
and 7% of hydroxyvalerate monomers. However, when the feeding mode was
changed to an aerobic/anaerobic one, the production of hydroxyvalerate monomers
increased to 30%, while the hydroxybutyrate monomers’ production dropped to
70% (Dai et al. 2007). Furthermore, experiments conducted by Amulya et al.
revealed that under microaerophilic environments and glucose as a substrate, the
content of hydroxyvalerate monomers increased to 21% compared to 8% under
aerobic conditions (Amulya et al. 2016).
5.4.3 Effects of Carbon Source and Raw Materials
Effect on Polyhydroxyalkanoates Composition
Many factors influence the final polyhydroxyalkanoates composition including the
type of substrate employed. Diverse monomer production is linked to substrates
containing a variety of volatile fatty acids (Serafim et al. 2008), making complex
industrial wastes an interesting feedstock where fermentation conditions could be
used to control the final polyhydroxyalkanoates product. Additionally, volatile fatty
acids with odd vs even chain lengths were also found to favor the production of
hydroxybutyrate or hydroxyvalerate (Morgan-Sagastume et al. 2015). Acetate is
one of the most popular carbon sources for polyhydroxyalkanoates production and
S. Sali and H. R. Mackey