Bioremediation of agricultural runoff and biopolymers production from cyanobacteria cultured in demonstrative full-scale photobioreactors

Abstract

The present work evaluated polyhydroxybutyrate (PHB) and carbohydrates production by wastewater borne cyanobacteria at demonstrative -scale (three photobioreactors (PBR) of 11.7 m 3 each), using agri- cultural runoff as feedstock. Agricultural runoff was fed to PBR1, which was devoted to cyanobacteria selection and biomass growth. In PBR2, inorganic carbon was added in a feast and famine regime to favour PHB-accumulating microorganisms. Finally, inorganic carbon was continuously added in PBR3 to boost PHB accumulation. A high removal efficiency of 95% and 99% for total nitrogen and phosphorus was obtained, respectively. Cyanobacteria were successfully selected and outcompeted green microal- gae. Results suggested that a minimum inorganic carbon concentration was needed to accumulate PHB while carbohydrates were accumulated only with CO 2 additions. Maximum concentrations of 4.5% VSS and 69% VSS for PHB and carbohydrates were obtained. Overall, this study shows at demonstrative -scale the potential of cyanobacteria to produce PHB within a wastewater biorefinery concept. And it gives insight on the strategies needed to produce PHB with cyanobacteria at massive scale.