Washington, November 18 An engineer has developed an inexpensive new method to remove oil sheen from water by repeatedly pressurizing and depressurizing ozone gas, creating microscopic bubbles that attack the oil so it can be removed by sand filters.

The engineer in question is Andy Hong, a professor of civil and environmental engineering, University of Utah, US.

"We are not trying to treat the entire hydrocarbon (oil) content in the water - to turn it into carbon dioxide and water - but we are converting it into a form that can be retained by sand filtration, which is a conventional and economical process," said Hong.

In laboratory experiments, Hong demonstrated that "pressure-assisted ozonation and sand filtration" effectively removes oil droplets dispersed in water, indicating it could be used to prevent oil sheen from wastewater discharged into coastal waters.

Hong conducted the study with two University of Utah doctoral students - Zhixiong Cha and Chia-Jung Cheng - and with Cheng-Fang Lin, an environmental engineering professor at National Taiwan University.

Hong said that his method uses two existing technologies - ozone aeration and sand filtration - and adds a big change to the former.

Instead of just bubbling ozone through polluted water, Hong uses repeated cycles of pressurization of ozone and dirty water, so the ozone saturates the water, followed by depressurization, so the ozone expands into numerous microbubbles in the polluted water. The tiny bubbles provide much more surface area - compared with larger bubbles from normal ozone aeration - for the oxygen in ozone to react chemically with oil.

According to Hong, pollutants tend to accumulate on the bubbles because they are not very water-soluble.

The ozone in the bubble attacks certain pollutants because it is a strong oxidant.

The reactions convert most of the dispersed oil droplets - which float on water to cause sheen - into acids and chemicals known as aldehydes and ketones.

Most of those substances, in turn, help the remaining oil droplets clump together so they can be removed by conventional sand filtration.

In his study, Hong showed the new method not only removes oil sheen, but also leaves the treated water so that any remaining acids, aldehydes and ketones are more vulnerable to being biodegraded by pollution-eating microbes.

"These are much more biodegradable than the parent compounds," he said.

With success in the laboratory, Hong now plans for larger-scale pilot tests. (ANI)