Production enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Halogeometricum borinquense, characterization of the bioplastic and desalination of the bioreactor effluent

Polyhydroxyalkanoates (PHAs) are a replacement of conventional single-use plastics. Bioprocess conditions of the extreme halophilic archaeon Halogeometricum borinquense strain RM-G1 were selected resulting in the synthesis of 66.80 ± 1.69 % PHA (of cell dry mass) in 72 h using glycerol and tryptone as carbon and nitrogen sources respectively, yielding volumetric productivity of 0.206 ± 0.006 gL−1 h−1 in a repeated batch process in a small-scale bioreactor where 20 % of the production medium was used as the inoculum for the subsequent batch. The purified PHA was characterized as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 10.21 mol% 3-hydroxyvalerate content possessing glass transition temperature -12.6 °C, degradation temperature 285 °C, number average molecular weight 156,899 Da, weight average molecular weight 288,723 Da, polydispersity index 1.8 and melting temperatures 139.1 °C and 152.5 °C. Maximum (21.7 ± 0.6 L m-2 h−1) and average (17.2 ± 0.6 L m-2 h−1) flux values were their respective highest and crystallization time was its least (3.0 ± 0.16 h) when ΔT was 90 °C and polytetrafluoroethylene membrane was applied for desalination of the bioreactor effluent by Direct Contact Membrane Distillation. While using polyvinylidene fluoride membrane, maximum 25.5 ± 0.5 L m-2 h−1 and average 18.6 ± 0.2 L m-2 h−1 fluxes were obtained and crystallization time decreased (3.25 ± 0.16 h) even when ΔT was lowered by 20 °C.