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Arthrospira (Spirulina) platensis Toliara isolated from alkaline and salt lakes in the south-western area of Madagascar is a potential source of proteins that could efficiently fight against food deficiency in developing countries like Madagascar. Up to now, productivity in this country has been low, so a better understanding of the growth conditions of this species is needed to improve its production. Growth experiments were undertaken in bubble columns at laboratory scale. The influence of agitation of the culture, medium salinity (ranging from 13 to 35 g L−1) and CO2 addition (ranging from 0 to 2%, v/v) on growth and protein content was examined. Because Arthrospira cells are fragile, a bubble column without additional mixing gave the best growth. Arthrospira (Spirulina) platensis showed higher specific growth rate (μmax) and protein content for lower salinity. Addition of 1% of CO2 improved the productivity by near 60%. The feasability of semi-continuous culture was demonstrated and optimal culture conditions led to a mean productivity of 0.22 ± 0.03 g L−1 d−1, a mean specific growth rate of 0.015 ± 0.002 h−1 and a protein content of 53 ± 2% of total dry weight.

Reactive extrusion involves complex interactions between operating parameters, flow conditions, material rheological behavior and reaction kinetics. Although reactive extrusion modelling has interested many authors, it still remains a challenge. We propose here a steady-state reactive extrusion model combining chemical engineering methods and simplified fluid mechanics laws. This steady-state model was derived from the dynamic model proposed by Choulak (2004). A rheo-kinetic model for a biopolymer oxidation process induced by coupled thermo mechanical and chemical effects was developed and integrated into the twin-screw extrusion model. This modelling approach enables to provide a predictive model involving very rapid calculation. The reactive extrusion model was then integrated into a static process simulator. The simulations reproduce available experimental data with a satisfying accuracy.