Cyanobacteria Biorefinery — Production of poly(3-hydroxybutyrate) with Synechocystis salina and utilisation of residual biomass

This study evaluates a biorefinery concept for producing poly(3-hydroxybutyrate) (PHB) with the cyanobacterial strain Synechocystis salina. Due to this reason, pigment extraction and cell disruption were investigated as pre-treatment steps for the harvested cyanobacterial biomass. The results demonstrated that at least pigment removal was necessary to obtain PHB with processable quality (weight average molecular weight: 569–988 kg mol^‐1, melting temperature: 177–182 °C), which was comparable to heterotrophically produced PHB. The removed pigments could be utilised as additional by-products (chlorophylls 0.27–1.98 mg g^‐1 TS, carotenoids 0.21–1.51 mg g^‐1 TS, phycocyanin 0–127 mg g^‐1 TS), whose concentration depended on the used nutrient source. Since the residual biomass still contained proteins (242 mg g^‐1 TS), carbohydrates (6.1 mg g^‐1 TS) and lipids (14 mg g^‐1 TS), it could be used as animal feed or converted to biomethane (348 m_n ³ t^‐1 VS) and fertiliser. The obtained results indicate that the combination of photoautotrophic PHB production with pigment extraction and utilisation of residual biomass offer the highest potential, since it contributes to decrease the environmental footprint of the process and because biomass could be used in a cascading way and the nutrient cycle could be closed.