High cell density culture of Chlamydomonas reinhardtii on acetate using fed-batch and hollow-fibre cell-recycle systems

Fed-batch culture was performed to minimise growth inhibition of Chlamydomonas reinhardtii by acetate in heterotrophic culture. Although the cell concentration obtained was higher than in batch cultures, it was eventually constrained by high sodium concentrations, which accumulated in the fermenter. The use of a continuous-flow, hollow-fibre cell-recycle system (HFCRS) using a membrane with a 0•2 μm pore size was successfully employed to overcome this problem. The HFCRS was run with no cell bleed to obtain a cell concentration of 9 g/l at a dilution rate of 0•1/h and a feed acetate concentration of 1•7 g/l. However, the cell growth yield under these conditions was poor. Using the same dilution rate and feed acetate concentration, a superior cell productivity of 0•083 g/l/h was achieved at a bleed ratio of 0•5. An unstructured mathematical model, incorporating the maintenance coefficient, was derived for the HFCRS. The model gave good agreement with experimental results, particularly at high bleed ratios, and predicted that higher cell concentration and productivity could be obtained using the HFCRS with a higher feed acetate concentration and dilution rate. The results demonstrate that the HFCRS is well suited to obtaining high concentrations of microalgae grown heterotrophically on inhibitory substrates.