Small amounts of oil leave a fluorescent sheen on polluted water that’s hard to remove — even when the water is aerated with ozone or filtered through sand. Now, a University of Utah engineer has developed an inexpensive new method to remove oil sheen by repeatedly pressurizing and depressurizing ozone gas, creating microscopic bubbles that attack the oil so it can be removed by sand filters. “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,” says Andy Hong, a professor of civil and environmental engineering. In laboratory experiments reported in Chemosphere, 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 says the method — for which patents are pending — also could be used to clean a variety of pollutants in water and soil, including so-called “produced water” from oil and gas drilling sites on land; water from mining of tar sands and oil shale; groundwater contaminated by MTBE, a gasoline additive that pollutes water through leaking underground gasoline storage tanks; “emerging contaminants,” such as wastewater polluted with medications and personal care products; and soil contaminated with polychlorinated biphenyls (PCBs, from electrical transformers), polycyclic aromatic hydrocarbons (PAHs, from fuel burning), or heavy metals.
The method uses two existing technologies — ozone aeration and sand filtration — but doesn’t just bubble ozone through polluted water. Instead, the system 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 — similar to the foaming of a carbonated beverage that’s opened too quickly. 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. Hong’s study showed the new method not only removes oil sheen but also leaves any remaining acids, aldehydes, and ketones in the treated water more vulnerable to destruction by pollution-eating microbes. The water is clean enough to be discharged after the ozonation and sand filtration, Hong says. With success in the laboratory, Hong now plans for larger-scale pilot tests. “It is economical and it can be scaled up,” he says. Meanwhile, the University of Utah Research Foundation has signed options to license the technology to Miracotech, Inc., of Albany, CA, and 7Rev, LP, a Salt Lake City VC group.
Source: The University of Utah News Center