Science - November 23, 2011

Early days for biodiesel from fungi

The fungus Umbelopsis isabellina stores oil in its cells which can be used as biodiesel. Except that on a diet of organic waste, it does not yet produce enough fungal oil – in spite of all PhD researcher Petra Meeuwse’s efforts.

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We can already make biodiesel out of palm oil, canola oil and deep-frying oil, but the search for sustainable sources still goes on. Meeuwse is looking into whether you can induce fungi that grow on organic waste to manufacture diesel oil. To do so you need to optimize the conditions for the fermentation of solids (in a compost heap, for example) or for the fermentation of fluids (in a reactor tank). Fungi use carbon and nitrogen to grow and carbon to stay alive. If you provide a fungus with plenty of carbon and little nitrogen, it cannot convert the energy into growth and stores the excess energy as oil. By doing this, Meeuwse aimed to produce as much fungal oil as possible.
When she tested fungi to see which one was best at converting nutrients into energy, the Umbelopsis isabellina fungus came out top. She then tested this fungus on sugar beet pulp, but she found that it only converted 5 percent of the pulp into fat. It was already known from the literature that the fungi perform better on sugars in a reactor tank. This was confirmed when Meeuwse tried growing the fungus in a tank containing glucose and nitrogen salts. Under these conditions the fungus made so much fat that it doubled in weight. Models developed from these experiments showed that 19 kilos of biodiesel can be produced from 100 kilos of sugar beet pulp in a reactor tank. 'Still not very much, but not bad for a first attempt.'
 Using the same models, Meeuwse could calculate how much biodiesel the ideal fungus could make: 25 to 30 kilos per 100 kilos of raw material. With a super-fungus like this, you can produce five times more energy than you put into it, she calculated. Her guess is that it is not economically viable to produce biodiesel in a reactor tank, because this method requires high levels of investment. The far cheaper solids fermentation process is promising, however. 'You cannot expect it to work perfectly right from the start. I am one of the first people in the world to research this thoroughly.'
Petra Meeuwse is due to receive her PhD from Hans Tramper, professor of Bioprocess Technology, on 30 November.
 

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