Cleaning oils using ozone bubbles

Small amounts of oil give rise to the brilliant sheen on polluted water. Removal of this oil is extremely difficult, even when the water is treated with ozone bubbles or filtered through sand. Now a more effective solution has been discovered - ozone

Small amounts of oil give rise to the brilliant sheen on polluted water. Removal of this oil is extremely difficult, even when the water is treated with ozone bubbles or filtered through sand. Now, a University of Utah engineer has developed a new and inexpensive method to remove this oil layer by repeatedly increasing and decreasing the pressure of ozone gas, creating microscopic bubbles that trap the oil and facilitate its subsequent removal through sand filtration.

"We don't try to treat the entire content of the hydrocarbon oil in the water - and turn it into carbon dioxide and water - but convert it into a form that can be treated afterwards by sand filtration, which is an acceptable and cost-effective process," says Andy Hong, professor of civil and environmental engineering at the University of Utah.

In laboratory experiments, which were recently reported in the scientific journal Chemosphere, the researcher demonstrated that a process of "ozonolysis with the help of pressure and filtration" effectively removes oil droplets dispersed in the water, a study indicating that this process can be used to prevent the pollution of coastal waters by an oil layer originating from water- trash.

The researcher claims that the proposed process - for which a commercial patent has been requested - could also be used to clean a variety of impurities in water and even in the soil, including:
1. Water that is produced together with oil and gas during drilling in the ground. This oily water is often discharged back into the ground pits. "If we have a method to clean this water we can use it again for irrigation and washing, especially in arid areas where every amount of water is important," explains the researcher.
2. Water originating from salt-sand and oil shale mining (shale stone, slate).
3. Groundwater contaminated with MTBE, a fuel additive that reduces vehicle emissions but pollutes the water due to leaking underground fuel storage tanks.
4. "Visible infections", such as sewage contaminated with medicines or personal hygiene products.
5. Soils contaminated with polychlorinated biphenyls (PCBs, electrical transformers) or polycyclic aromatic hydrocarbons (PAHs, from burning fuel).
6. Soils contaminated with heavy metals.
7. Waste water from refineries and oil spills in factories or waterways.

The researcher points out that his method combines two existing methods - ozone bubbling and sand filtration - and improves them, especially the bubbling. Instead of just bubbling ozone through the contaminated water, the researcher uses repeated cycles of bubbling pressurized ozone into the contaminated water until it is saturated and then reducing the pressure so that the ozone expands into many micro-bubbles, similar to the way carbonated beverage liquids flow if the container is opened quickly.

The tiny bubbles provide a much wider surface area - compared to the larger ozone bubbles obtained in the previous process - and allow for an increase in the chemical reaction between the oxygen atoms of the ozone and the oil. The researcher explains that pollutants tend to accumulate on the bubbles because they are not soluble in water. The ozone found in the bubbles "attacks" certain pollutants since it is a strong oxidizer.

The reaction with the ozone converts most of the oil droplets dispersed in the water, or in the soil, to acids and chemicals known as aldehydes and ketones. Most of these substances, in turn, help the remaining oil droplets to gather together and then can be easily removed by sand filtration.
In his research, the scientist showed that his new method not only removes the oily layer, but also leaves the treated water in such a way that the acids, aldehydes and ketones in it (organic substances) can be better discharged by organisms that feed on them.

The researcher claims that the water is clean enough after the process for irrigation, but additional methods can be applied to it that also break down the organic substances dissolved in it.

During his experiments, the researcher found that oily water was cleaned optimally by using ozone bubbling rounds under pressure and reducing this pressure ten times, then filtering it through sand, then putting this water through twenty more rounds of pressure and reducing it, then filtering it again through sand. The researcher examined the nature of the bubbling process by measuring chemical and biological oxygen indices for the water samples. These two indices indirectly examine the content of organic substances in the water. The researcher also used the method of mass spectrometry to identify the types of impurities remaining in the treated water.

He found that his most effective procedure succeeds in removing about ninety-nine percent of the impurities (turbidity) in water originating from oil drilling - while obtaining clear water at the level of drinking water - and removing eighty-three percent of the oil.

After his success in the laboratory, the scientist is now planning experimental tests on a larger scale. "The process is economical, and can be made industrial," notes the researcher.

The researcher mentions that other methods were indeed developed in the past to treat oil-contaminated water and that they had varying levels of success. They include: centrifuges, filter membranes, a normal ozone bubble, and an air bubble to keep the pollutants out. However, all these methods have disadvantages, such as the lack of ability to treat dissolved oil or high concentrations of it.

Not one of the methods individually - sand filtration and ozone bubbling - was able to effectively treat oil-contaminated water. The researcher explains that long-chain oil particles do not readily react with ozone without added pressure and that sand filters alone are unable to remove oil contamination.

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