Feasibility of attached cultivation for polysaccharides production by Porphyridium cruentum

Porphyridium cruentum is one of the most valued microalgae species able to produce both pigments and exopolysaccharides. Conventional liquid suspended cultivation in ponds and photobioreactors show its disadvantages in lower cultivation efficiency and higher stirring power consumption due to the high viscosity of the medium by the accumulation of polysaccharides. In this work, a new method of culture (called attached cultivation) based on the growth of microalgae using a supporting surface was successfully applied to the cultivation of P. cruentum and the effect of the main influential parameters on its growth rate and polysaccharides production has been investigated. Higher values of these factors resulted in a faster growth rate and, in particular, optimum values of 6.98 g m^-2 for initial biomass density, 100 µmol m^-2 s^-1 for light intensity, continuous illumination, 2.0 % for CO₂ concentration, and 0.1 v v^-1 min^-1 for aeration rate produced the best polysaccharide production of 42 % dry weight. The nutrition profile of P. cruentum obtained in attached and suspended cultivations was similar. Overall these results demonstrate that the attached cultivation is a promising technique which greatly improves the growth rate of P. cruentum as well as its production of polysaccharides and, therefore, it is worth enhancing to be exploited for commercial application.