Ethanol Production From Tetraselmis Subcordiformis Biomass

When coupled with ethanol fermentation, CO2 produced by the fermentation can be carbon source for microalgae growth, and the microalgae biomass harvested could be an alternative feedstock for ethanol production. In this study, Tetraselmis subcordiformis, a unicellular marine phytoplankton microalga that can accumulate starch intracellularly under specific conditions, was cultivated with CO2 produced by ethanol fermentation, and ethanol production from the microalgae biomass was investigated.First, the enzymatic method was developed to analyze starch content accumulated intracellularly during the culture of T. subcordiformis. Then, the microalgae culture was carried out in a 10 L flat-plate photobioreactor sparged with CO2 commercially available, and the biomass concentration of 1.85 g(DCW)/L was achieved at the 7th day, in which 45.6% was starch accumulated intracellularly. Meanwhile, continuous ethanol fermentation was carried out with a 1.5 L fermentor, through which effluent contained 65.4 g/L ethanol and 8.7 g (DCW)/L yeast biomass was discharged continuously when the medium containing 150 g/L glucose was fed at the dilution rate of 0.065 h-1, and the productivity of CO2 was calculated to be 4.07 g/(L.h). Based on mass balance, the two systems were coupled by sparging CO2 produced by the ethanol fermentation into the photobioreactor, and the biomass concentration of 1.98 g/L was achived within the photobioreactor at the 7th day, in which 43.8% was starch accumulated intracellularly.Furthermore, the pretreatment of microalgae biomass with a solid contration of 20% was examined. For the acid hydrolysis treatment, more than 80% starch was converted into glucose when treated by 3%(v/v) sulfuric acid at 120℃for 60 min or 5%(v/v) sulfuric acid at 110℃for 45 min. For the enzymatic treatment, all starch was recovered. These experimental results indicated that the pretreatment of microalgae biomass is simple and similar to that applied to starch-based feedstocks.Finally, two strategies:separated hydrolysis and fermentation (SHF) and simulatenious saccharification and fermentation (SSF) were explored for ethanol production from microalgae biomass or microalgae biomass supplemented with corn meal. And the experimental data indicated that higher ethanol concentration and productivity were achived with the SSF strategy,10.5% and 10.8% increase in ethanol concentration and 2.3% and 1.1% increase in ethanol productivity, compared with the SHF strategy.