Simultaneous use of sodium nitrate and urea as nitrogen sources improves biomass composition of Arthrospira platensis cultivated in a tubular photobioreactor

Arthrospira platensis is widely cultivated in open ponds for industrial purposes. However, high-protein A. platensis biomass produced in photobioreactors (PBRs) is recommended for pharmaceutical and cosmetic formulations. A. platensis was cultivated in a 3.5 L tubular airlift PBR using both sodium nitrate and urea as nitrogen sources. Sodium nitrate was added from the start of the cultivation using a batch process. Urea was supplied daily at exponentially increasing feeding rate using a fed-batch process. The simultaneous optimization of the independent variables, namely, total quantity of sodium nitrate (m(T1)) and total quantity of urea (m(T2)), led to an optimal condition of m(T1) = 15.0 mmol/L and m(T2) = 7.5 mmol/L. Maximum biomass concentration (5183 +/- 94 mg/L) corresponding to the highest biomass productivity (683 +/- 13 mg/L/day) was obtained under such condition. The addition protocol of both nitrogen sources resulted in high productivities of protein (6.2 +/- 0.4 mg/L/day) as well as chlorophyll-a (372.2 +/- 7.7 mg/L/day). Such innovative process could be applied in the large-scale production of A. platensis using tubular PBR for novel applications.