BACKGROUND: Fed-batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires the knowledge of kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow-rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: We obtained the optimal values of T=32 °C and U=1.16 mM d-1, under which the maximum cell concentration was 4186±39 mg L-1, cell productivity 541±5 mg L-1 d-1 and yield of biomass on nitrogen 14.3±0.1 mg mg-1. Applying an Arrhenius-type approach, we estimated the thermodynamic parameters of growth (ΔH* = 98.19 kJ mol-1; ΔS* = -0.020 kJ mol-1 K-1; ΔG* = 104.1 kJ mol-1) and its thermal inactivation (ΔHd° = 168.9 kJ mol-1; ΔSd° = 0.459 kJ mol-1 K-1; ΔGd° = 31.98 kJ mol-1). CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts.
Kinetic and thermodynamic investigation of Arthrospira (Spirulina) platensis fed-batch cultivation in a tubular photobioreactor using urea as nitrogen source
CONVERTI, ATTILIO;
2012-01-01
Abstract
BACKGROUND: Fed-batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires the knowledge of kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow-rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: We obtained the optimal values of T=32 °C and U=1.16 mM d-1, under which the maximum cell concentration was 4186±39 mg L-1, cell productivity 541±5 mg L-1 d-1 and yield of biomass on nitrogen 14.3±0.1 mg mg-1. Applying an Arrhenius-type approach, we estimated the thermodynamic parameters of growth (ΔH* = 98.19 kJ mol-1; ΔS* = -0.020 kJ mol-1 K-1; ΔG* = 104.1 kJ mol-1) and its thermal inactivation (ΔHd° = 168.9 kJ mol-1; ΔSd° = 0.459 kJ mol-1 K-1; ΔGd° = 31.98 kJ mol-1). CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts.
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