Is Ozone The Best Technology For Micropollutants?

By Peter Chawaga

Micropollutants are one of the problems that continue to vex the wastewater treatment field. They continue to infect waterways, pouring in from sources like pharmaceutical and personal care products (PPCPs), pesticides, and industrial chemicals, endangering wildlife and possibly reaching consumers. Meanwhile, their persistent and non-biodegradable nature makes them resistant to many traditional wastewater treatment practices.

Switzerland provides an interesting case study on the growing fight against micropollutants. The Swiss Water Protection Act has been updated to require certain wastewater treatment plants to actively reduce their input of organic micropollutants into surface waters over the next 25 years, according to Christian Abegglen, leader of the Swiss Wastewater Association team responsible for equipping plants with anti-micropollutant technology. While the plants are free to choose technologies that will work best for them, in many cases Abegglen recommends ozonation as the best solution.

“When dissolving ozone in water, ozone molecules attack certain chemical bindings,” he said. “So, the target molecules are ‘attacked’ and oxidized. The drawback of ozonation is that we do not exactly know which reaction products are formed. But in large pilot experiments in Regensdorf and Lausanne, we were able to show that water quality increases in general.”

The process involves mixing ozone gas and wastewater using a diffuser or injector pipes that make use of the “Venturi effect.” The ozone breaks down micropollutants into a benign form. Stateside, some companies have been offering ozonation solutions for years as a way to combat the growing threat of micropollutants.

“Ozonation is a cost-efficient and sustainable means of eliminating micropollutants,” said Harald Stapel, industrial and process sales manager for Xylem. “It provides a chemical-free means of removing 90 percent of emerging contaminants. It can be quite simply incorporated into existing and new applications and is a reliable and control-supported process.”

In Switzerland, some wastewater treatment plants choose granular activated carbon (GAC) to satisfy their micropollutant restrictions. Abegglen pointed out that because activated carbon absorbs micropollutants instead of altering them, they are completely removed from wastewater once the activated carbon is disposed of. But even when activated carbon is put to use, ozonation can have a role to play.

“The only validated alternative technology [to ozonation] in Europe is the use of GAC filters and they are typically used in combination with ozone,” said Alex Bettinardi of De Nora Water Technologies. “The advantage of ozonation is the direct oxidation, breaking the molecule. Molecules are destroyed and not only absorbed… Ozonation is surely one of the best treatment options when used in combination with other technologies like GAC or biological filtration.”

Stapel pointed out that activated carbon is also less versatile and sometimes up to 40 percent more expensive than ozonation.

While Switzerland has imposed micropollutant regulations on some of its wastewater treatment plants, the U.S. EPA has not.

“While there is a growing concern and increasing awareness about the serious threat posed by micropollutants, regulation lags behind,” said Stapel. “However, it is only a matter of time before treatment operations will be required to incorporate treatment steps to ensure that micropollutants are eliminated and do not enter the water system.”

Stapel pointed out that in the U.S., “contaminants of emerging concern” like micropollutants may not be federally regulated but that some states have taken action against them with health- or risk-based action levels. Other micropollutants are regulated under the Safe Drinking Water Act. They may also be regulated under the National Discharge Elimination System when risks are posed to aquatic life.

Aside from considering ozonation to deal with a specific micropollutant, it may emerge as a key player in the growing realm of recycled drinking water.

“Ozone has been ‘rediscovered’ for water reuse as a best available technology since it can both disinfect and oxidize, or be used with other technologies in a multiple-barrier concept,” Stapel said. “For micropollutants that are under consideration for regulation or that are perceived to be an obstacle to getting the public to accept water reuse, ozone can proactively and efficiently address those concerns to get both public and regulatory acceptance.”

As micropollutants continue to plague wastewater and regulations promise to become more stringent, it may be time for more treatment plants to consider ozone.