11-29: Bioethanol production from macroalgae: third generation biofuel

The increase on demand for biofuel has been pressing agricultural sector to expand crop areas and competing with food crops. As an alternative way to circumvent these issues is the exploration of new frontiers for harvesting, among cellulignin biomasses, algal carbohydrates can became an important source of bioethanol. The organism evaluated in this report is photosynthetic macro-algae, or “seaweed”. Kappaphycus alvazerii are classified as red seaweed, or Rhodophyceae, source of galactan.

Considering the advantages of bioethanol production with algal biomass, and the lack of studies over algal fermentation for renewable fuel, the purpose of this investigation was to evaluate the possibilities of acid and enzymatic hydrolysis, simultaneous glucose and galactose fermentation, and simultaneous saccarifcation and fermentation.

The study ranges for diluted acid hydrolysis concentration was 0,1 to 2,0% (v/v), and 10 to 60 minutes at 121ºC,  which generated a liquid fraction (rich in galactose), and the cellulose residue (CR). For the enzymatic hydrolysis of CR, a central composite rotational design was carried out using enzyme loading (20-70 FPU/g CR) and CR concentration (10-22% w/v) as independent variables.

The fermentation of liquid fraction and enzymatic hydrolysate was promoted by Saccharomyces cerevisiae CBS1782, batchwise in a Biostat B reactor in the follow reactional conditions: galactose and glucose concentration of 70 and 55 g/L, recpectively, which result in 40 g/L of ethanol at 88 h of fermentation.

These preliminaries results indicate good prospects as a potential feedstock for bioethanol production.