The fundamental components required
for scaling up the production
of biogas-based biopolymers can be provided through a single process,
that is, anaerobic digestion (AD). In this research, the possibility
of enriching methane-utilizing mixed cultures from the AD process
was explored as well as their capability to accumulate polyhydroxyalkanoates
(PHAs). For almost 70 days of operation in a fed-batch cyclic mode,
the specific growth rate was 0.078 ± 0.005 h–1 and the biomass yield was 0.7 ± 0.08 mg-VSS/mg-CH4. Adjusting the nitrogen levels in AD centrate resulted in results
comparable to those obtained with a synthetic medium. The enriched
culture could accumulate up to 51 ± 2% PHB. On the other hand,
when the culturing medium was supplemented with valeric acid, the
enriched bacteria were able to produce polyhydroxybutyrate-co-valerate (PHBV) up to 52 ± 6% with an HV percentage
of 33 ± 5%. Increasing the valeric acid concentration in the
culturing medium above 100 mg/L decreased the overall amount of PHBV
by 60%, whereas the number of HV units incorporated was not affected.
Changing the methane-to-oxygen ratio (M/O) from 1:1 to 4:1 caused
an almost 80% decline in PHB accumulation. In addition, M/O had a
significant effect on the fraction composition of PHBV at different
valeric acid concentrations.
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