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it may be necessary to add specific substrates to augment low-strength and complex
wastewaters. Under mixed volatile fatty acids, feeding interactions between various
volatile fatty acids is also key to consider, as well as the mode of operation and
specific organisms that develop within the microbial mixed culture system.
In a pure culture experiment conducted by Mukhopadhyay et al., the effect of
various acids on the accumulation of polyhydroxyalkanoates by Rhodopseudomonas
palustris was evaluated under the same conditions. Acetate was found to produce
the highest polyhydroxybutyrate content of 15.1% of cell dry weight, while malonate did not result in any polyhydroxyalkanoates accumulation. Other acids tested
included malate, butyrate, citrate, and fumarate as well as glycerol, which accumulated 7.7%, 7.5%, 5.91%, 3.99%, and 3.41%, respectively (Mukhopadhyay et al.
2005). In a different experiment conducted by Yu et al., they evaluated the effects of
various concentrations of butyrate and valerate on polyhydroxyalkanoates accumulation of Cupriavidus metallidurans. The results revealed that the highest polyhydroxyalkanoates accumulation of 0.41 g-polyhydroxyalkanoates/g-cell was
achieved at a mixture of 80:20 butyrate/valerate, while the lowest accumulation of
0.06 g-polyhydroxyalkanoate/g-cell was achieved at 100% of valerate (Yu et al.
1998). The preference and ability to synthesize polyhydroxyalkanoates, however,
varies from organism to organism. For instance, Rhodopila globiformis, an anoxygenic phototroph, does not convert acetate, but rather has a preference for ethanol
and glucose (Imhoff et al. 2005). Hence, variations in substrate in a mixed culture
will lead to changes in dominant organisms in the microbial community. New process conditions should therefore match the conditions suitable for enrichment of
target organisms known to effectively store polyhydroxyalkanoates on a given
substrate.
In certain instances, substrates can be inhibitory to polyhydroxyalkanoates production. For instance, Wang et al. demonstrated that butyrate and valerate can inhibit
the conversion of acetate and propionate (Wang et al. 2018). In another study,
Korkakaki et al. (Korkakaki et al. 2016) showed that in a mixed substrate influent of
acetate and methanol only acetate led to polyhydroxyalkanoates accumulation,
under the specific process environment, whereas methanol promoted nonpolyhydroxyalkanoates storing organisms. By ending the feast phase and decanting
the remaining methanol during the cycle, the authors managed to increase the accumulated cell polyhydroxyalkanoates from 48% to 70% wt. by preventing excess cell
biomass growth on methanol (Table 5.2).
5.4.4 Feeding Regime
There are two groups of bacteria with the ability to produce polyhydroxyalkanoates.
The first group creates polyhydroxyalkanoates in case of nutrient limitation such as
oxygen, nitrogen, phosphate, or magnesium (Choi and Lee 1999). The second group
does not demand nutrient limitation and can accumulate polyhydroxyalkanoates
during the exponential growth phase (Chee et al. 2010). Generally, accumulation in
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
it may be necessary to add specific substrates to augment low-strength and complex
wastewaters. Under mixed volatile fatty acids, feeding interactions between various
volatile fatty acids is also key to consider, as well as the mode of operation and
specific organisms that develop within the microbial mixed culture system.
In a pure culture experiment conducted by Mukhopadhyay et al., the effect of
various acids on the accumulation of polyhydroxyalkanoates by Rhodopseudomonas
palustris was evaluated under the same conditions. Acetate was found to produce
the highest polyhydroxybutyrate content of 15.1% of cell dry weight, while malonate did not result in any polyhydroxyalkanoates accumulation. Other acids tested
included malate, butyrate, citrate, and fumarate as well as glycerol, which accumulated 7.7%, 7.5%, 5.91%, 3.99%, and 3.41%, respectively (Mukhopadhyay et al.
2005). In a different experiment conducted by Yu et al., they evaluated the effects of
various concentrations of butyrate and valerate on polyhydroxyalkanoates accumulation of Cupriavidus metallidurans. The results revealed that the highest polyhydroxyalkanoates accumulation of 0.41 g-polyhydroxyalkanoates/g-cell was
achieved at a mixture of 80:20 butyrate/valerate, while the lowest accumulation of
0.06 g-polyhydroxyalkanoate/g-cell was achieved at 100% of valerate (Yu et al.
1998). The preference and ability to synthesize polyhydroxyalkanoates, however,
varies from organism to organism. For instance, Rhodopila globiformis, an anoxygenic phototroph, does not convert acetate, but rather has a preference for ethanol
and glucose (Imhoff et al. 2005). Hence, variations in substrate in a mixed culture
will lead to changes in dominant organisms in the microbial community. New process conditions should therefore match the conditions suitable for enrichment of
target organisms known to effectively store polyhydroxyalkanoates on a given
substrate.
In certain instances, substrates can be inhibitory to polyhydroxyalkanoates production. For instance, Wang et al. demonstrated that butyrate and valerate can inhibit
the conversion of acetate and propionate (Wang et al. 2018). In another study,
Korkakaki et al. (Korkakaki et al. 2016) showed that in a mixed substrate influent of
acetate and methanol only acetate led to polyhydroxyalkanoates accumulation,
under the specific process environment, whereas methanol promoted nonpolyhydroxyalkanoates storing organisms. By ending the feast phase and decanting
the remaining methanol during the cycle, the authors managed to increase the accumulated cell polyhydroxyalkanoates from 48% to 70% wt. by preventing excess cell
biomass growth on methanol (Table 5.2).
5.4.4 Feeding Regime
There are two groups of bacteria with the ability to produce polyhydroxyalkanoates.
The first group creates polyhydroxyalkanoates in case of nutrient limitation such as
oxygen, nitrogen, phosphate, or magnesium (Choi and Lee 1999). The second group
does not demand nutrient limitation and can accumulate polyhydroxyalkanoates
during the exponential growth phase (Chee et al. 2010). Generally, accumulation in
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…