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Researchers in Iran have discovered a fungus that can metabolise and absorb sulfur from crude oil and so reduce one of the major sources of air pollution when petroleum products are burned. The fungus is more effective than any chemical engineering solution used in conventional oil refineries.

Sarah Torkamani, Jalal Shayegan, Soheila Yaghmaei, and Iran Alemzadeh of the Chemical and Petroleum Engineering Department, Sharif University of Technology, Tehran, Iran, point out that existing processes for refining so-called “heavy,” or high-sulfur, crude oil convert sulfur to hydrogen sulfide gas at high temperatures and pressures. The main aim is to reduce the noxious sulfur-containing gases released by burning oil fuels. These are often acidic and can cause health problems in some people, damage the urban environment and lead to acid rain, which affects trees, plants, and lakes, for instance.

Necessary emission standards on fossil fuels could be more easily met with the use of such a biotech cleanup option, the researchers say. "Oil supplies 38% of the worldwide energy, and as the light oil is limited and meanwhile the energy demand is increasing, it is a must to use heavy crude oil and therefore desulfurize it to meet environmental standards," the team says. "It is not feasible to desulfurize all the sulfur-containing compounds in heavy crude oil using existing methods, such as hydro-desulfurization," they add.

Scientists have known for a long time that the biochemistry of certain microbes is suited to removing sulfur from oil. However, the development of a biodesulfurization method using such microbes to treat heavy crude oil has not been found to be viable until now. Indeed, desulfurization with a bacterial agent requires the oil to be heated to 45 Celsius to activate the process, which uses a lot of energy.

In the new study, Torkamani and colleagues explain how they isolated and tested the first microbial fungus, known as Stachybotrys species WS4, which can remove sulfur from heavy crude oil. The fungus is capable of removing 65 to 76% of the sulfur content from crude samples at two different oil fields, the Soroush and the Kuhemond oil fields, where initial sulfur content is 5 and 7.6% by weight, respectively.

The team has studied the impact of several variables on heavy crude oil biodesulfurization, such as initial pH of the medium, the water to oil ratio, and the number of fungal spores added to the sample. The researchers point out that the process works without the need for energy-hogging high temperatures or pressures, requiring heat just above room temperature, at 30 Celsius, which is presumably readily accessible to oil refineries in the Middle East much of the time.

The work was carried out as a project initiated by the Petroleum Engineering Development Company (PEDEC), a subsidiary of the National Iranian Oil Company.

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