Biodiesel, glycerol and Microorganisms

Economic, political, social and environmental factors related to the growing world concern with the use of fossil fuels propel research in the search for alternative energy sources derived from renewable resources.  In this scenario, one of the promising alternatives to substitute the petroleum-derived diesel oil is biodiesel, a fuel produced by renewable sources of energy such as vegetable oils (soyabean, dendê, castor beans, etc.) and animal fats. One method used to produce biodiesel is the transesterification of oils and fats. One method used to produce biodiesel is the transesterification of oils and fats. It consists in the chemical reaction of the oil or fat with a mono short-chain alcohol (methanol or ethanol) on the presence of a catalyst (acid or basic), leading to the formation of mono-esters (biodiesel) and glycerine (glycerol gross). The ratio between these two products is around 10% of the total glycerin in total biodiesel produced.

The National Program of Biodiesel Production and Using (PNPB) introduced this biofuel on Brazilian energy matrix by Law n º 11097 of January 13, 2005. This law establishes the whole diesel oil commercialized in the country must contain 5% of biodiesel up to 2013. That rule was anticipated by Resolution n º 6 / 2009 of the National Energy Policy (CNPE) and the percentage of 5% became mandatory since 1st January 2010. In this year, production of biodiesel was 2.4 billions of liters, leading; consequently, an increase of glycerin available in the market which makes the price of this product drop. On the other hand, the glycerin excess could cause serious losses, if released into the environment. Other problem is that this material provides impurities and wastes from the production process and the needs for its purification treatment are economically inviable. Thus, the crude glycerol must not be used by industries that requiring purest compound, for example, the food, pharmaceutical and cosmetics, and should therefore look for new options for using its viability.

Because it is very common and abundant in nature several microorganisms are able to use glycerol as carbon sources. For this reason, the possible destinations to the material resulting from the manufacture of biodiesel is their use as a constituent of culture media, for growth of microorganisms in biotechnological processes, which lead to the production of molecules of economic interest. Several chemical compounds of commercial importance – ethanol, succcínico acid, propionic acid, citric acid, pigments, biosurfactant, biopolymers, etc. – could be produced by microorganisms were grown in crude glycerol (da Silva et al., 2009). The yeast Pichia pastoris of industrial use, for example, is highly promising candidate because it can reach a high cellular density taking glycerol as a carbon source. This yeast is widely used to produce heterologous proteins of commercial interest (Cregg et al., 2000), among them α-amylase, α-galactosidase, β-lactamase, β-galactosisidase, endoglucanase, peroxidase and various other substances.One interesting application is using enzymes expressed by P. pastoralists in the production of animal feed. Phytase, acid phosphatase, cellulase and hemicellulase are some examples of enzymes expressed by this yeast used in the industry of animal feed. This industry represents an important sector of agribusiness in the country and measures to help the economic development, allowing a cost reduction in the production, is of high interest.

Creating environmentally friendly alternatives, to use of waste coming from renewable sources of energy is an area with great opportunity to research and investment. Solutions that create added value products economically advantageous are a great challenge for research relating to the agroenergy throughout the world. Some products, which are now petroleum derivatives can at first, be produced biotechnologically by microorganisms, that use glycerol as substrate. This would bring economic benefits for the environment and therefore promote the use of biodiesel, reducing oil dependence, reduce gases emission of greenhouse and increase the production of chemical products, food, feed meals, etc.

Source: Biomassa & Bioenergia,   December 5th 2011.

By Paula F. Franco, Analista Embrapa Agroenergy

Translated by Gilberto Silber Schmidt

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