“Microbial oil production using heterotrophic oleaginous yeasts and renewable feedstocks”

Jong-In Han

Department of Civil and Environmental Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea

jihan@kaist.ac.kr

Wendesday 22nd May
H117-3 Thorvaldsensvej 40

 Oleaginous yeast has become some of the most promising feedstock for biodiesel production due to their high production efficiency. However, high cost of cultivation hinders the commercialization of biodiesel on the basis of the yeast. As an effort to reduce the cost, my research group has utilize cheap substrates including lignocellulose, and Jerusalem artichoke, activated sludge (WAS).

Although lignocellulose is one of a few truly renewable feedstocks in an meaningful amount, it has a very complex structure and requires pretreatment step to be utilized by oleaginous microbes. My group has tested existing methods and developed new ones including FeCl3 –based treatment, alkali, and sono-assisted dilute sulfuric acid process. FeCl3 oxidation of xylose and lignin led to the reduction of iron from ferric iron (Fe3+) to ferrous iron (Fe2+). Furthermore, this ferrous iron was completely oxidized at anode in a fuel cell generating a power. Thus, FeCl3 oxidation proved a green process that could be successfully employed for integrated energy production system using waste species (agriculture residue, Fe2+).

WAS is a good feedstock candidate due to high content of organic carbon and nutrients. Most bioavailable components, however, exist within the cells and/or in the solid state, and thus its proper disintegration is required before its use as a substrate for the microbial growth. One effective way of pretreating activated sludge is hydrodynamic cavitation (HC) especially under alkaline condition. HC can be simply generated by a constriction using orifice plate. Subsequently, HC is collapsed, temperature within micro-bubble may be several thousand kelvin and pressure is several atmospheres.

Jerusalem artichoke (JA) is a non-food crop composed with inulin. JA plant grows well on even under suboptimal conditions and requires limited human interruption for cultivation. An average yield is also good; higher than that of other crops, such as corn, potato, and sweet-potato. Among various acids that have been used to pretreat it, we selected nitric acid. This acid require less treatment time to produce sugar with limited generation of inhibitors. In addition, nitrate (NO3-), which is produced upon nitric acid (HNO3) is neutralized, serves as N source for the oleaginous cell growth.

To obtain optima conditions for all the cases, a statistical approach, termed Response surface methodology (RSM), was used. With the pretreated feedstocks, we obtained quite promising results, in terms of cell dry weight, lipid content, and quality: sometime even better than with simple commercial sugars such as glucose, fructose, and yeast extract.