Autotrophic production of polyhydroxyalkanoates using acidogenic-derived H2 and CO2 from fruit waste

[Display omitted] •First reported evidence of PHA autotrophic accumulation from biogenic H2 and CO2.•Under autotrophic conditions, C. necator DSM 545 increased 3HB accumulation of 42%.•Two reactors: (i) acetogenesis of melon waste; (ii) H2 and CO2 fermentation in PHA.•To boost H2 and CO2, methanogenesis was stopped and OLR increased to 20 gCOD/L/d.•13 gCOD/L of VFAs and alcohols were also produced and converted into 3HB and 3HV. The environmental concerns regarding fossil plastics call for alternative biopolymers such as polyhydroxyalkanoates (PHAs) whose manufacturing costs are however still too elevated. Autotrophic microbes like Cupriavidus necator, able to convert CO2 and H2 into PHAs, offer an additional strategy. Typically, the preferred source for CO2 and H2 are expensive pure gases or syngas, which has toxic compounds for most PHAs-accumulating strains. In this work, for the first time, H2 and CO2 originating from an acidogenic reactor were converted autotrophically into poly(3-hydroxybutyrate) P(3HB). During the first stage, a mixed microbial community continuously catabolized melon waste into H2 (26.7 %) and CO2 (49.2 %) that were then used in a second bioreactor by C. necator DSM 545 to accumulate 1.7 g/L P(3HB). Additionally, the VFAs (13 gCOD/L) produced during acidogenesis were processed into 2.7 g/L of P(3HB-co-3HV). This is the first proof-of-concept of using acidogenic-derived H2 and CO2 from fruit waste to produce PHAs.