Investigating and modelling the effect of sodium bicarbonate on the synergy of acetate and propionate on Rhodobacter sphaeroides growth for wastewater treatment

Rhodobacter sphaeroides can be used as a promising candidate for biotechnological resource recovery because of their metabolic versatility. This investigation has employed varying concentrations of sodium bicarbonate at optimal light intensity and synergy of acetate and propionate to examine their effects on the growth of Rh. sphaeroides , as well as on the contents of polyhydroxyalkanoate, protein, and carbohydrate. Acetate-mediated growth at optimal light intensity produced 0.35 g/L of biomass, with polyhydroxyalkanoate extraction yield, carbohydrate and protein contents of 63.70 ± 3.27 mg PHA/g biomass, 2.78 ± 0.51 % w/w and 12.75 ± 0.87 % w/w, respectively, after 7 days. At optimum dosage of 0.9 g/L of sodium bicarbonate, in conjunction with the optimal light intensity and acetate and propionate synergy, 1.25 g/L of biomass was produced, with polyhydroxyalkanoate extraction yield, carbohydrate, and protein contents of 140.83 ± 12.78 mg PHA/g biomass, 7.11 ± 0.47 % w/w and 39.25 ± 0.60 % w/w, respectively. The biomass yield and protein content decreased at 1.2 g/L of sodium bicarbonate, while the polyhydroxyalkanoate content increased, and the carbohydrate content remained unchanged. The simultaneous use of inorganic carbon (sodium bicarbonate) and organic carbon (acetate and propionate) at the optimal light intensity is an efficient technique for enhancing the biomass yield and the synthesis of metabolites, including polyhydroxyalkanoate, protein, and carbohydrate, paving the path for large-scale cultivation and application in wastewater remediation. These metabolites possess diverse uses, including the production of bioplastics from PHA, animal feed from protein, and biofuels from carbohydrate. • The optimal light intensity for cultivation of Rhodobacter sphaeroides is 40 W/m 2 . • The synergy of acetate and propionate produces higher biomass. • Increasing sodium bicarbonate dose improves cell growth and metabolite contents. • The model simulation validates the experimental results (R 2 = 0.81). • The contents of PHA, protein, and carbohydrate are estimated and analysed.