Yeast Cultivation can also Produce Biodiesel from Renewable Waste Resources

The production of biodiesel from algae and microorganisms is a viable alternative to the usual methods of production which include crushed oilseeds and waste vegetable oil (WVO). Most people already know about the use of algae that is currently being developed for a number of different types of biofuels, another possible source of fatty acids for biodiesel that hasn't received much attention can be cultivated using microorganisms or yeast cells. Microorganisms or algae could be the favorable choice in biofuel production due to the theoretical high yield amount of biomass per acre as compared to conventional energy crops which usually include oilseeds such as soybeans. It is estimated that alternative biomass sources such as algae produce 30 times more energy value than these conventional crops. Several yeast cell varieties that have been experimented in with in the past can produce high fatty acids amounts per cell and along with high lipid yeilds. Three types of yeast varieties, those being Cryptococcus Curvatus, Lipomyces Starkeyi & Rhodotorula Glutinis can attain a cell lipid percentage of up to 60 - 70 % [ 1. X. Meng et al 2009 ]. An advantage with the cultivation of yeast cells for biofuels is that they can be grown using dark fermentation. Dark Fermentation is a term that usually applies mostly towards the production of biohydrogen from microrganisms. However, similar fermentation conditions and even carbon feedstocks work for the cultivation of yeasts even though they are not the same choice of microorganisms that usually make hydrogen. However, the same type renewable waste resources used for biohydrogen production can also be applied towards the cultivation of yeast cells towards lipid production. These type of renewable waste sources include wastewater sources, dairy wastes, starch hydrosylates, lignocellulosic wastes and even biodiesel glycerine waste.

Yeast cells also have the advantage of attaining high biomass yields in a short period of time. The growth rate of yeast as well as the actual conversion rate of a carbon source into lipids are very good. For example, with batch style fermentation, yeasts attain cell density yields of around 100 - 150 grams cells per liter, while lipid production rates are around 0.2 - 0.5 grams lipid per liter * hour and a carbon conversion rate of up to 30 % [ 2. P. Measters et al 1996 ]. High lipid yields can be attained by providing an excess amount of carbon feedstock as well as providing a lower nitrogen content in the growth media. In other words having a high carbon to nitrogen (C/N ratio) - (a similar concept in producing a good compost) and other factors such as favorable Temperature, pH and oxygen content provide higher lipid yields [ 3. L. Azocar et al 2010 ]. Companies are already using yeasts to produce biofuels although not towards the manufacture of lipids. One company currently cultivates yeast cells to make isoprenes. Isoprenes represent a large class of natural compounds produced by many organisms, of which plants usually produce a large subset of these compounds called terpenoids. Isoprene, which is a related compound can also be produced by microorganisms. It is used to make materials like rubber. The cost of producing biofuels from microorganisms or algae have some obstacles to overcome, such as processing and refining methods, costs and associated technology improvement needs. Production of biofuels from algae, microorganisms or yeasts may still be a favorable method of choice due to the possible availability of renewable waste resources as carbon sources to produce lipids. The production of biodiesel itself has the potential to manufacture even more biodiesel from the cultivation of yeast cells from the glycerine waste that may accumulate in large quantities as more biodiesel is produced. For example, it is estimated that for every 10 kg of biodiesel produced from certain oilseeds around 1 kg of waste glycerine is made. It is also estimated that even at the current production rate, the pharmaceutical industry only needs 1/3 of the glycerine produced to help manufacture drugs.

REFERENCES

1. "Biodiesel Production from Oleaginous Microorganisms", Renewable Energy vol 34 pg 1-5 [2009] by Xin Meng, J. Yang, Xin Xu, L. Zhang, Q. Nic, M. Xien

2. "High Density Cultivation of the Lipid Accumulating Yeast Cryptococcus Curvatus using Glycerol as a Carbon Source", Applied Microbiology & Biotechnology vol 45 pgs 575-579 [1996] by PAEP Measters, GNM Huijbents

2. "Biotechnological Processes for Biodiesel Production Using Alternative Oils", Applied Microbiology & Biotechnology vol 88 No 3 pg 621-626 by L. Azocar, G. Ciudad, HJ Heipieper, R. Navia

Photos taken from the Picasa Web Album

KEYWORDS: Cryptococcus Curvatus, Lipomyces Starkeyi, Dark Fermentation, Renewable Waste Resources, Biodiesel Glycerine, Isoprenes, High Production Biomass, Yeast based Biodiesel, High Lipid Percentage per cell, Rhodotorula Glutinis, Starch & Whey Hydrosylates

Photos taken from the Web Album of Picasa

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