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

Abstract

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 ± 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 °C (M₁) and 55 °C (M₂) were supplied to promote 3-HV inclusion. Results showed that pure valeric acid supported the highest polymer yields of 105.8 ± 9 g m^-3d^-1 (3-HB:3-HV=70:30). M₁ mixtures led to a maximum of 103 ± 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.

Keywords: Biopolymers; Biorefinery; Poly(3-hydroxybutyrate-co-3-hydroxyvalerate); Sustainable process; Volatile fatty acids.