Oil companies may be able to clean up their fuel to meet tightening emissions standards using a recently discovered humble fungus
Oil companies may be able to clean up their fuel to meet tightening emissions standards using a recently discovered humble fungus. The fungus removes the sulphur and nitrogen compounds that lead to acid rain and air pollution and grows naturally in crude oil.
Governments worldwide, are imposing increasingly severe limits on how much of those compounds fuels can contain. Oil producers are searching for more efficient ways to strip sulphur and nitrogen from their products.
The standard way to "desulphurise" crude oil involves reacting it with hydrogen at temperatures of 455 °C and up to 204 times atmospheric pressure (roughly 21 million pascals or 3000 psi). It achieves less than perfect results.
Micro-organisms able to metabolise sulphur and nitrogen have the potential to achieve the same endpoint under more normal conditions. In recent years a number of researchers have isolated desulphurising bacteria.
But Jalal Shayegan and his team at the Sharif University of Technology in Tehran, Iran, have now discovered and isolated a fungus that appears able to remove sulphur from oil with greater efficiency.
Shayegan's team went looking for fungus in oil-contaminated soil from Tehran oil refinery and the Kuhemond oil field in Iran, and isolated a number of new desulphurising micro-organisms.
Tests revealed that one strain of Stachybotrys fungus was particularly efficient at sulphur removal – the first fungus found to have this ability.
Shayegan's team pitted their new find against several known desulphurising bacteria. They grew them all for 6 days on heavy crude oil samples from the Kuhemond and Soroush oil fields, mixed with a water-based growth medium.
The fungus achieved the best results by far. In one sample it removed 76% of sulphur compounds in just 3 days, a figure only one bacteria could match over the full 6 days.
Robin van Leerdam at Wageningen University in Bomenweg, Netherlands, says biodesulphurisation holds promise as a method to refine oil and that the new contender is a welcome addition.
But he says rematches are required to properly test it against the known bacteria. "The sulphur removal efficiency of the fungus is higher than of the bacterium, but the comparison is not completely fair," he told New Scientist.
The desulphurising bacteria pitted against the fungus were previously grown on Dibenzothiophene, commonly used to simulate the sulphur compounds in crude oil. But they had not been grown before on crude oil itself. Leerdam thinks bacteria more used to crude oil would run the fungus closer for efficiency.
Other researchers are still advancing non-biological approaches to stripping sulphur from oil.
"If you want to invest in desulphurisation technologies then put your money on the chemical route," Michiel Makkee at Delft University of Technology in Julianalaan, Netherlands told New Scientist.
His team recently designed a simple ester capable of removing sulphur from diesel. It works 10 or 20 times faster than a fungus or bacteria, and could be squeezed into much more compact reactors than a biological process, Makkee says.
But he concedes that his new method still requires heat – working at 140 °C compared to the fungus' room temperature.