The co-conversion of methane and mixtures of volatile fatty acids into poly (3-hydroxybutyrate-co-3-hydroxyvalerate) expands the potential of an integrated biorefinery

In this work, the potential of Methylocystis hirsuta to simultaneously use methane and volatile fatty acids mixtures for triggering PHBV accumulation was assessed for the first time batchwise. Biotic controls carried out with CH4 alone confirmed the inability of Methylocystis hirsuta to produce PHBV and achieved 71.2 & PLUSMN; 7 g m- 3d-1 of PHB. Pure valeric acid and two synthetic mixtures simulating VFAs effluents from the anaerobic digestion of food waste at 35 degrees C (M1) and 55 degrees C (M2) were supplied to promote 3-HV inclusion. Results showed that pure valeric acid supported the highest polymer yields of 105.8 & PLUSMN; 9 g m- 3d-1 (3-HB:3-HV=70:30). M1 mixtures led to a maximum of 103 & PLUSMN; 4 g m- 3d-1 of PHBV (3-HB:3-HV=85:15), while M2 mixtures, which did not include valeric acid, showed no PHV synthesis. This suggested that the synthesis of PHBV from VFAs effluents depends on the composition of the mixtures, which can be tuned during the anaerobic digestion process.

Automated summary

This study assessed the potential of Methylocystis hirsuta to use methane and volatile fatty acids mixtures for triggering PHBV accumulation. Bioreactors with methane alone confirmed the inability of Methylocystis hirsuta to produce PHBV and achieved a PHB yield of 71.2 ± 7 g m- 3d-1. The inclusion of pure valeric acid and different synthetic mixtures influenced the synthesis of PHBV, suggesting that the composition of the mixtures can be adjusted during the anaerobic digestion process.