Effects of Photobioreactor Depth on Stichococcus Cultures Aimed at Biodiesel Production

Abstract

Biofuels production by microalgae is a challenging process known since the end of the last century. Bio-oil extracted from microalgae may be adopted as crude fuels or may be transesterified to biodiesel. Key aspects for industrialization of microalgae-to-biofuel processes are: selection and improvements of algal strains; development of high-performance photobioreactor; improvement of oil extraction and transesterification. The present contribution regards the effects of reactor design on biodiesel production by Stichococcus bacillaris of Naegeli genus. The attention was focused on the effects of the depth of sub-horizontal flat photobioreactors on the performances of continuous cultures. Two rectangular shape columns were investigated of depth 5 and 8 cm.
Semi-continuous conditions were investigated as regards the biomass suspension. Tests were carried out at 23°C and pH 7. The continuous irradiance level was set at 240 µE m^-2s^-1, gas flow rate at 0.5 vvm, CO₂ concentration in the gas stream set at 2%v. Cultures were characterized in terms of pH, concentration of total nitrogen, total organic carbon, total inorganic carbon, biomass, lipids fraction and methyl-ester distribution of transesterified lipids.
Results pointed out that the performance of the photobioreator decreased with the photobioreactor depth: the specific productivity referred to the irradiated surface increased when the light path decreased.