BIOETHANOL AND BIODIESEL PRODUCTION WITHIN A CYANOBACTERIA AND MICROALGAE BIOREFINERY

MARÍA EUGENIA SANZ SMACHETTI; CAMILA DENISE CORONEL; LARA SÁNCHEZ RIZZA; MAURO DO NASCIMENTO

Córdoba

Congreso; XI Congreso Argentino de Microbiología General; 2015

SAMIGE- Asociación Civil de Microbiología General

Oleaginous microalgae have great potential as a feedstock for biodiesel and other biofuels. However, the current cost of producing biofuels from microalgae biomass is still high to envision massive and profitable commercialization in the near future.One of the drawbacks of implementing large-scale cultivation of these organisms is the unsustainable requirement of N-fertilizers. It is presumed, however, that co-production of higher value by-products in the frame of a biorefinery would increase the profitability of producing biofuels and co-products from microalgae. Recently, we showed the efficient conversion of N2 -fixing cyanobacterial biomass into oleaginous microalgae biomass. We further modeled an integrated bioprocess that would require no N-fertilizer other than air and would yield 7.000 - 10.000-l microalgae oil . ha-1. year-1 in raceway ponds placed insoutheastern Buenos Aires. This estimated yield would be 2- to 20-fold higher than that reported for current oleaginous plant feedstocks heavily fertilized with conventional N-fertilizers. In addition to oil, this process would roughly produce from 2 kg ofNostoc biomass about 1 kg of Nostoc residues (mostly carbohydrates) and 1.0 kg of carbohydrates and 1 kg protein from Chlorella sorokiniana biomass. In this study, we obtained data of Nostoc productivity under Mar del Plata city environmental conditions in autumn in 5-l air bubbled photobiorreactors that further support the previous productivity model and found conditions of phosphorous deficiency for optimizing the carbohydrate to protein ratio of the biomass for a biorefinery. Both cyanobacterial and microalga carbohydrates could be hydrolyzed into soluble sugars in diluted acid (0.3 % H2SO4) at 100 °Cfor 1h with efficiencies higher than 85 %. These conditions are mild in comparison with those normally used for saccharification of lignocelulosic biomass for second generation bioethanol, supporting the convenience of using cyanobacteria/microalgaebiomass as a suitable alternative. We further used saccharified cyanobacterial biomass as a feedstock to produce bioethanol by fermentation with the Baker?s yeast Saccharomyces cerevisiae. We observed that yeasts fermented the syrup into ethanol at 11% of the theoretical maximum conversion in the absence of yeast growth, while control experiments with hydrolyzed dextrose reached 28 % of the theoretical maximum at 20 h. Current work in our laboratory is focused towards improving, at a laboratory scale, the most critical steps of a conceptual bioprocess for the biorefinery of cyanobacteria/microalgae/yeast biomass for the co-production of biodiesel, bioethanol and protein to be used as biofuel and feed, respectively.