133
is controlled. Hashimoto et al. explored the impact of pH on polyhydroxyalkanoates
production in Rhodospirillum rubrum grown in an acetate environment. The highest
polyhydroxyalkanoates accumulation reached 0.67 g-polyhydroxyalkanoates/g-dry
cell at pH 7 (Hashimoto et al. 1993). For pure cultures, experiments were conducted
on Pseudomonas aeruginosa. The highest yield of polyhydroxybutyrate of 60% cell
dry weight was reached at a pH of 7 with peptone as a nitrogen source (Muralidharan
et al. 2013). A research conducted by Gomaa et al. evaluated the impact of pH on
polyhydroxyalkanoates production on Bacillus subtilis and Escherichia coli in similar environments. The highest polyhydroxyalkanoates accumulation was observed
at pH of 7 at 62.2% and 58.7% for Bacillus subtilis and Escherichia coli, respectively (Gomaa 2014).
An experiment conducted by Amulya et al. on the impact of pH for the production of polyhydroxyalkanoates in various microbial mixed culture environments
revealed that a pH of 7 was more beneficial to the dehydrogenase enzyme activity
and substrate degradation compared to acidic and alkaline conditions in a microaerobic environment. These conditions showed an increase in polyhydroxyalkanoates accumulation to 56% at pH 7 compared to lower polyhydroxyalkanoates
accumulation in acidic and basic environments (Amulya et al. 2016). Experiments
of pH impact on polyhydroxyalkanoates production with microbial mixed culture
under nitrogen-limiting conditions revealed that environments with no-pH control
led to very alkaline conditions and produced up to 44% of polyhydroxyalkanoates
cell dry weight. With pH control between 8.8 and 9.2, the polyhydroxyalkanoates
content increased up to 51% polyhydroxyalkanoates cell dry weight with a pH value
ranging from 8.8 to 9.2 (Montiel-Jarillo et al. 2017). Moreover, both yield and polyhydroxyalkanoates production rates also increased with increasing pH. Other studies conducted on microbial mixed cultures producing polyhydroxyalkanoates
revealed a production of higher amounts of hydroxyvalerate monomers in case of
pH 9.5 compared to a pH of 5.5 under the same conditions (Dionisi et al. 2005).
Pittman et al. conducted an experiment on wastewater as a substrate and evaluated
the effects of pH on the production. A pH of 8 was the best operating condition for
a high and stable production of polyhydroxyalkanoates achieving 28.4% of cell dry
weight, whereas a pH of 6 halted the accumulation of polyhydroxyalkanoates inside
the cells (Pittmann and Steinmetz 2014).
5.4.7 Temperature Effect
Very few studies evaluated the impact of temperature on polyhydroxyalkanoates
production. However, based on various experiments, the ideal temperature of polyhydroxyalkanoates production varies depending on the type of bacterial strains
involved in the process and seems to range from ambient temperature to
30 °C. Experiments conducted on the effects of temperature on microbial mixed
culture growth and polyhydroxyalkanoates accumulation have shown that the ideal
polyhydroxyalkanoates accumulation occurs at a temperature of 15 °C when fed
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
is controlled. Hashimoto et al. explored the impact of pH on polyhydroxyalkanoates
production in Rhodospirillum rubrum grown in an acetate environment. The highest
polyhydroxyalkanoates accumulation reached 0.67 g-polyhydroxyalkanoates/g-dry
cell at pH 7 (Hashimoto et al. 1993). For pure cultures, experiments were conducted
on Pseudomonas aeruginosa. The highest yield of polyhydroxybutyrate of 60% cell
dry weight was reached at a pH of 7 with peptone as a nitrogen source (Muralidharan
et al. 2013). A research conducted by Gomaa et al. evaluated the impact of pH on
polyhydroxyalkanoates production on Bacillus subtilis and Escherichia coli in similar environments. The highest polyhydroxyalkanoates accumulation was observed
at pH of 7 at 62.2% and 58.7% for Bacillus subtilis and Escherichia coli, respectively (Gomaa 2014).
An experiment conducted by Amulya et al. on the impact of pH for the production of polyhydroxyalkanoates in various microbial mixed culture environments
revealed that a pH of 7 was more beneficial to the dehydrogenase enzyme activity
and substrate degradation compared to acidic and alkaline conditions in a microaerobic environment. These conditions showed an increase in polyhydroxyalkanoates accumulation to 56% at pH 7 compared to lower polyhydroxyalkanoates
accumulation in acidic and basic environments (Amulya et al. 2016). Experiments
of pH impact on polyhydroxyalkanoates production with microbial mixed culture
under nitrogen-limiting conditions revealed that environments with no-pH control
led to very alkaline conditions and produced up to 44% of polyhydroxyalkanoates
cell dry weight. With pH control between 8.8 and 9.2, the polyhydroxyalkanoates
content increased up to 51% polyhydroxyalkanoates cell dry weight with a pH value
ranging from 8.8 to 9.2 (Montiel-Jarillo et al. 2017). Moreover, both yield and polyhydroxyalkanoates production rates also increased with increasing pH. Other studies conducted on microbial mixed cultures producing polyhydroxyalkanoates
revealed a production of higher amounts of hydroxyvalerate monomers in case of
pH 9.5 compared to a pH of 5.5 under the same conditions (Dionisi et al. 2005).
Pittman et al. conducted an experiment on wastewater as a substrate and evaluated
the effects of pH on the production. A pH of 8 was the best operating condition for
a high and stable production of polyhydroxyalkanoates achieving 28.4% of cell dry
weight, whereas a pH of 6 halted the accumulation of polyhydroxyalkanoates inside
the cells (Pittmann and Steinmetz 2014).
5.4.7 Temperature Effect
Very few studies evaluated the impact of temperature on polyhydroxyalkanoates
production. However, based on various experiments, the ideal temperature of polyhydroxyalkanoates production varies depending on the type of bacterial strains
involved in the process and seems to range from ambient temperature to
30 °C. Experiments conducted on the effects of temperature on microbial mixed
culture growth and polyhydroxyalkanoates accumulation have shown that the ideal
polyhydroxyalkanoates accumulation occurs at a temperature of 15 °C when fed
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…