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mixed culture fed with acetate-limited conditions and intermittent feeding that polyhydroxybutyrate accumulated up to 90% of cell dry weight (Beccari et al. 1998).
Fradinho et al. explored the effects of malate, citrate, lactate, acetate, propionate,
and butyrate on polyhydroxyalkanoates accumulation in phototrophic microbial
mixed cultures under continuous light. While microbial mixed culture fed with
malate, citrate, and lactate did not accumulate polyhydroxyalkanoates, cultures fed
with acetate, propionate, and butyrate were able to store polyhydroxyalkanoates
(Fradinho et al. 2014). While the mixed culture reduces polyhydroxyalkanoates
production costs significantly, it produces a low cell density compared to the pure
cultures, which can make subsequent extraction steps more costly (Kourmentza
et al. 2017).
5.4.2 Redox Environment
Reports on the impact of redox environment on polyhydroxyalkanoates production
are mixed. In the study of Gumel et al., it was observed that aerobic environments
resulted in a lower accumulation of polyhydroxybutyrate compared to anaerobic
ones, which is related to the shift of cellular activities caused by the availability of
oxygen (Gumel et al. 2013). The cells shift to produce energy-intensive protein and
glycogen because of the availability of NAD+ and ATP under aerobic conditions
and halt the production of polyhydroxyalkanoates due to the energy-rich nature of
aerobic oxidation reactions (Saharan et al. 2014; Third et al. 2002). In a sequencing
batch reactor experiment with acetate as the carbon source, it was revealed that at
lower dissolved oxygen conditions, the acetate conversion rate was low, but the
majority of the substrate was converted to polyhydroxybutyrate compared with
higher dissolved oxygen conditions. The low ATP available was used for the transportation of acetate into the cells (Third et al. 2002). Another experiment testing the
impact of the redox environment on polyhydroxyalkanoates production revealed
that microaerobic environments produced higher polyhydroxyalkanoates content up
to 56% of cell dry weight compared to only 34% of cell dry weight under aerobic
conditions (Amulya et al. 2016). Similar findings in a separate study showed cell
dry weight storage can be increased from 20% and 33% under anaerobic and aerobic conditions, respectively, to 62% in a microaerophilic-aerobic sludge process
(Satoh et al. 1998).
In contrast, some experiments have found that polyhydroxyalkanoates production rates using aerobic systems are higher. For instance, a study using a sequencing
batch reactor found polyhydroxyalkanoates conversion yields of 0.7–0.9 C-mol/Cmol (Filipe et al. 2001) compared to anoxic conditions 0.4–0.5 C-mol/C-mol (Beun
et al. 2002). Similarly, Wang et al. evaluated the effect of dissolved oxygen on the
substrate competition and polyhydroxyalkanoates production in microbial mixed
cultures with mixed volatile fatty acids as carbon source. The change of dissolved
oxygen levels in the environment affected the polyhydroxyalkanoates storage capability and yield, where a high dissolved oxygen level resulted in high
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
mixed culture fed with acetate-limited conditions and intermittent feeding that polyhydroxybutyrate accumulated up to 90% of cell dry weight (Beccari et al. 1998).
Fradinho et al. explored the effects of malate, citrate, lactate, acetate, propionate,
and butyrate on polyhydroxyalkanoates accumulation in phototrophic microbial
mixed cultures under continuous light. While microbial mixed culture fed with
malate, citrate, and lactate did not accumulate polyhydroxyalkanoates, cultures fed
with acetate, propionate, and butyrate were able to store polyhydroxyalkanoates
(Fradinho et al. 2014). While the mixed culture reduces polyhydroxyalkanoates
production costs significantly, it produces a low cell density compared to the pure
cultures, which can make subsequent extraction steps more costly (Kourmentza
et al. 2017).
5.4.2 Redox Environment
Reports on the impact of redox environment on polyhydroxyalkanoates production
are mixed. In the study of Gumel et al., it was observed that aerobic environments
resulted in a lower accumulation of polyhydroxybutyrate compared to anaerobic
ones, which is related to the shift of cellular activities caused by the availability of
oxygen (Gumel et al. 2013). The cells shift to produce energy-intensive protein and
glycogen because of the availability of NAD+ and ATP under aerobic conditions
and halt the production of polyhydroxyalkanoates due to the energy-rich nature of
aerobic oxidation reactions (Saharan et al. 2014; Third et al. 2002). In a sequencing
batch reactor experiment with acetate as the carbon source, it was revealed that at
lower dissolved oxygen conditions, the acetate conversion rate was low, but the
majority of the substrate was converted to polyhydroxybutyrate compared with
higher dissolved oxygen conditions. The low ATP available was used for the transportation of acetate into the cells (Third et al. 2002). Another experiment testing the
impact of the redox environment on polyhydroxyalkanoates production revealed
that microaerobic environments produced higher polyhydroxyalkanoates content up
to 56% of cell dry weight compared to only 34% of cell dry weight under aerobic
conditions (Amulya et al. 2016). Similar findings in a separate study showed cell
dry weight storage can be increased from 20% and 33% under anaerobic and aerobic conditions, respectively, to 62% in a microaerophilic-aerobic sludge process
(Satoh et al. 1998).
In contrast, some experiments have found that polyhydroxyalkanoates production rates using aerobic systems are higher. For instance, a study using a sequencing
batch reactor found polyhydroxyalkanoates conversion yields of 0.7–0.9 C-mol/Cmol (Filipe et al. 2001) compared to anoxic conditions 0.4–0.5 C-mol/C-mol (Beun
et al. 2002). Similarly, Wang et al. evaluated the effect of dissolved oxygen on the
substrate competition and polyhydroxyalkanoates production in microbial mixed
cultures with mixed volatile fatty acids as carbon source. The change of dissolved
oxygen levels in the environment affected the polyhydroxyalkanoates storage capability and yield, where a high dissolved oxygen level resulted in high
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…