By: Editorial Team Reading time: 3 Minutes
Ozone cracks pollutants
Ozone is extremely reactive. Waste treatment plants put that property to good use – by converting noxious drug residues into harmless substances, for example. Ozonation plays an increasingly important role in sewage treatment.
Diclofenac is one of the most commonly used active ingredients against joint pain and inflammation. As an ointment, it is even available over the counter. After using it, however, the human body secretes 70 percent of the drug unchanged. In Germany alone, some 63 tons of this substance make it into the sewage system every year. Water treatment plants using the conventional three steps – mechanical, biological and chemical – only break it down to a limited extent. The sizable quantity that remains is discharged into the watercourse where it becomes a danger to the fish population.
This painkiller is just one example of a whole range of complex organic compounds with considerable potential for harm. Many substances of this type, from antibiotics to corrosion inhibitors to pesticides, can also cause significant damage if they remain in the water cycle – even though they are classified as “micropollutants” in the overall balance sheet of wastewater. Water protection is now a high priority in most countries. More and more water treatment plants today include additional purification steps that also act on this substance group. Since 2016, the ARA wastewater treatment plant in Reinach in northern Switzerland has been using a fourth stage that treats the wastewater with ozone.
From the swimming pool to the wastewater treatment plant
“The ozonation of water is a proven method that’s been used against viruses and bacteria in swimming pools for a long time now,” explains plant manager Reto Pfendsack. “With its tremendous reactivity, the ozone also attacks problematic molecules in the wastewater and converts them into harmless substances.” There are also a few compounds, however, that really should not be treated with ozone, such as ones that could generate toxic bromates. “We first had our wastewater analyzed in a special laboratory,” says the ARA’s manager. “They confirmed that it’s suitable for ozonation.”
Just three grams per cubic meter
On average, between two and three grams of ozone per cubic meter are now added to Reinach’s wastewater. Diffusers – fine pored ceramic distributors – introduce it as tiny bubbles with a large total surface area into the basin, where the oxidation reactions occur. “The process is easy to handle, not labor-intensive, and considerably less expensive than alternative methods,” explains the wastewater treatment plant pro. The effectiveness of the ozone treatment is regularly monitored using twelve indicator substances, including Diclofenac and Benzotriazol. Laboratory results confirm that it renders most of the micropollutants harmless. ARA can then pump the purified water into the local stream, the Wyna, without hesitation. The ozone molecule (O₃) is very unstable, however, so the gas can be neither transported nor stored. ARA uses high voltage to produce it itself from oxygen (O₂) in an ozone generator. Messer supplies the oxygen.