Microbial cogeneration of biofuels.

摘要

The fields of biodiesel and bioethanol research and development have largely developed independently of one another. Opportunities exist for greater integration of these processes that may result in decreased costs of production for both fuels.;To that end, this work addresses the use of the starches and glycerol from processed algal biomass as substrates for fermentation by the yeasts Saccharomyces cerevisiae and Pachysolen tannophilus, respectively. Ethanol producers commonly employ the former yeast for ethanol production and include the latter yeast among candidate species for cellulosic ethanol production.;A simple 95% ethanol extraction at 70°C followed by sulfuric acid hydrolysis at 121°C and 2 atm proved a sufficient pretreatment for S. cerevisiae fermentation of starch from Chlamydomonas reinhardtii mutant cw15. The maximum rate of ethanol production was observed as 14 mL/g-h and a maximum concentration of 0.9 +/- 0.01% (m/v) was observed by 28 hours. Some starch appeared invulnerable to hydrolysis.;P. tannophilus fermentation of glycerol, both independently and among mixed substrates, was likewise demonstrated. It was found that glucose consumption preceded that of glycerol and xylose, but that the latter two substrates were consumed concurrently. Under aerobic, batch conditions, the maximum specific growth rate of the species on a 2% glycerol substrate was observed as 0.04/hr and the yield coefficient for conversion of glycerol to ethanol was 0.07 g/g. While the maximum observed concentration of ethanol in the glycerol-only fermentation was 0.1% m/v, that in mixed media containing 2% each glucose, xylose, and glycerol was 1.5%.;Also investigated here was the flocculation of a mutant species of the algae C. reinhardtii by a combination of methanol and calcium. Algae harvest is typically an energy-intensive process, but the technique demonstrated here is not. Complete flocculation of cells was observed with only 5 minutes of mixing and less than 10 minutes of settling using 12 mM CaCl2 and 4.6% methanol. Ethanol was observed to operate in the same capacity, intimating another area in which yeast bioethanol and algal biodiesel processes might enable one another. During growth, either an inhibitor of flocculation was produced or a facilitator was consumed.