1st Assessment

Since my presented objectives were long-term goals, I have not met them.  They were proposed to be achieved by the end of the semester. Yet, we have been making some progress towards these objectives. Concepts from all of our proposals were merged and we have developed a statistical study directed to find the optimum growth conditions during fermentations with P. Stipitis. Therefore, I could say that on the progress scale from 1 to 5 we would get a 2. The main difficulty here is going to be time because the poster session date is early in the semester considering our objectives were set for the end of it.

Eitherway, we have submitted our abstract for the poster session. If you are interested in our topic of producing cellulosic ethanol, you may read our abstract provided below.

Bioprocess Engineering Studies to Improve Production of Cellulosic Ethanol

Optimizing xylose-fermentation processes involving Pichia Stipitis

Biofuels stand today as a serious solution to the volatilely-priced fossil fuels, first as very poor producers of greenhouse gases (GHG) and second, as being less energy-intensive in process and production stages than their counterparts (Lago et.al., 2006). Obtaining ethanol from sugar cane bagasse is regarded as a possible source of this alternative fuel for two reasons: it does not hinder food accessibility and, reduces solid waste generation from sugar cane processing. Cellulose, hemicellulose and lignin are the main components of bagasse: cellulose can be hydrolyzed into glucose yet hemicellulose is hydrolyzed into glucose and other pentoses, where xylose is abundant. Unlike glucose, xylose can only be fermented by a limited number of yeast strains. A previous screening study showed that Pichia stipitis NRRL Y-11545, was the best xylose fermenting strain, although it was found to have a poor growth rate during experiments. This project aims to study the effects of environmental factors on P. stipitis growth under anoxic conditions in batch fermentation reactors. Xylose fermentation by P. stipitis can be optimized by performing fermentations for each selected parameter combinations in order to achieve higher ethanol yields, cell growth and substrate consumption. Maximum and minimum values in a 23 factorial design for initial xylose concentration, temperature and agitation are 50-80 g/L, 30-40°C, and 80-125 rpm respectively. A minimum of two runs will be run at each of these values in order to observe the interaction of these variables with each other. To control the inoculum quality, the initial culture will be preserved in glycerol so that each batch run will have an inoculum with the same effectiveness. Malt extract will be added as a new ingredient to the batch culture media. Batch culture data for the effect of the combinations will be analyzed by means of periodical optical density measurements, dry biomass weighting and HPLC analysis for xylose and ethanol. The factorial design experiments will be analyzed using an ANOVA (Analysis of Variance) with MINITAB, a statistical software. Previous experiments found in literature have confirmed that higher initial xylose concentration increases the ethanol production, since higher amount of cells are available for ethanol conversion. In addition, experiments executed around 30˚C have produced higher overall yield. Finally, low agitation level (50-100 rpm) has been proven to achieve higher ethanol production.