Feasibility of microbial biodiesel and carotenoid production considering the potential of food processing wastewaters as low cost carbon sources using the example of red yeast Rhodotorula glutinis

摘要

Due to the increasing demand for sustainable biofuels, microbial oils as feedstock for the transesterification into biodiesel have gained scientific and commercial interest. Also microbial carotenoids have a considerable market potential as natural colorants. Against this background this thesis assessed the feasibility of biodiesel produced by heterotrophic microorganisms, particularly yeasts, using the example of oleaginous red yeast Rhodotorula glutinis. To improve the economic efficiency of this process, several studies have been conducted in order to test (i) whether wastewaters from the agricultural processing industry can be utilized as low-cost carbon and nutrient source for growth and lipid production by R. glutinis and (ii) if they also facilitate the simultaneous production of beta-carotene and other carotenoids as high-value by-products. It has been shown at a small scale, that agricultural processing wastewaters can be used as feedstock for the microbial production of lipids and carotenoids.The general discussion continues to assess the approach of microbial biodiesel production in a broader context in terms of its economic, environmental and energetic performance. The calculated break-even price of microbial oil, excluding the cost of the carbon source for fermentation, is around double the price of conventional plant oils as competing products. To reduce the costs, cultivation in open raceway ponds was proposed, which led to a cost reduction of around 20 %. In order to assess the potential environmental benefits different life cycle assessments from algae biodiesel production, which share common features with the proposed process, have been analyzed. It was concluded, that microbial biodiesel cannot outperform common 1st generation biodiesel in terms of GHG emissions, whereas factors of eutrophication potential and land competition could be significantly improved. The high climate relevant emissions were mainly driven by the high energy requirements connected to the extraction of microbial oil, which also puts a heavy burden on the energetic efficiency of the process. Considering the potential of continued research and technical development along with the political commitment to promote 2nd and 3rd generation biofuels, it was concluded, that in the long term microbial biodiesel could become a commercial reality above laboratory and pilot scale. Due to the different restrictions this will probably not happen within the next 20-30 years.Contrary to biodiesel, carotenoids are high-value products, with beta-carotene yielding around US$ 600 per kg. Sustained by this high price and allowing for certain improvements regarding beta-carotene yields and extraction techniques, it can be possible to economically and sustainable produce beta-carotene from R. glutinis in the near future.