Bathing sites near urban areas frequently have problems with poor water quality caused by waste water discharges. Kemira’s disinfectant DesinFix cleans bathing water quickly with no hazardous substances remaining in the water.

Heavy rainfall has occurred more frequently in the last 50 years. The models used to predict future global warming predict that we will see more extreme weather events in the future.

Heavy rain can lead to bathing water being contaminated with fecal bacteria from waste water discharges. Kemira’s disinfectant system  DesinFix restores water quality. Photo: T. Brorson.

”In affected regions, storm- and waste water systems are often unable to keep up with the increasing volumes of water”, says Bengt Hansen, Kemira. ”There is an apparent risk that polluted water reaches the drinking water or bathing waters, with outbreaks of infectious disease as a possible outcome. Intestinal infections caused by E. Coli bacteria, for instance”.

Urban beaches are at peril

Having a bathing site nearby is attractive to city-dwellers. But in many locations, bathing is sometimes banned due to poor water quality. In Helsingborg, Sweden, it is not unusual for local authorities to advice against bathing because of intestinal bacteria in the water.

Another city having issues with the bathing water is Biarritz, France. In 2013, the waste water treatment facilities were overloaded by heavy rainfall. Untreated water was released into the sea near the Grand Plage and Port the Pêcheurs beaches, with dire consequences. Concentrations of fecal bacteria rose to hazardous levels. Bathing was banned, causing reactions from residents, tourists and local businesses. The city of Biarritz knew something had to be done quickly. Conventional disinfection methods like ultrafiltration, ozone treatment, chlorification and UV treatment require expensive equipment, and it takes time to get it in place.

”It was then Kemira entered the scene with the disinfectant system DesinFix. The technology was already being used in Ile d’Oléron, France, Venice, Italy and Berlin, Germany, and the city of Biarritz decided to try the system as well. The system was in place before the tourist season began in 2014, and bacterial concentrations (E. Coli) quickly dropped to levels well below the threshold values. Together with external researchers, we have used the Biarritz facility to evaluate the technology’s efficiency and what effect is has on marine ecosystems. We found no toxic effects on plants or animals, since DesinFix quickly breaks down into carbon dioxide and water, and leaves no byproducts. Nor did we find any negative effects on cement constructions. We consider DesinFix to be a cost-efficient and environment-friendly solution to bacterial contamination of water. We hope that the city of Helsingborg will try it, too”, Bengt Hansen says.

What about the chemicals?

The disinfectant is highly reactive, and has to be mixed on location in an automated process. Photo: Kemira.

The chemicals used in the system are highly reactive and have to be handled with care. DesinFix is based on a mixture of formic acid (HCOOH) and hydrogen peroxide (H2O2) and when accurately mixed, these two components form the highly efficient active substance performic acid (HCOOOH). The substance is unstable, so DesinFix needs to be mixed on location and then immediately distributed to the water in need of treatment. The performic acid decomposes in the water to form hydroxyl radicals that kill the bacteria by breaking down their cell wall. Neither the bacteria nor the performic acid remains afterwards, the only thing left is carbon dioxide and water.

”It takes only a few minutes to disinfect the water, and within an hour after dosing the active substance can no longer be detected. No toxic disinfection byproducts are left in the water, so the usage of chemicals is not a matter of concern”, Bengt Hansen says.

”The disinfectant has to be produced on-site by mixing the chemicals. We have developed a compact, standardized mixing unit, called DEX-3. A typical installation fits in a 2x2x1 meter box, and consists of two storage tanks for the chemicals, two transfer pumps and a fully automated mixing unit. The disinfectant is fed to the water at an appropriate flow rate; no large amounts are required, a few grams of DesinFix is enough to purify a cubic meter of water. It uses little energy and it comes with minimal maintenance requirements, which results in a lower cost than competing methods”.

”The method is an excellent solution for waste water disinfection after heavy rainfall. Beaches in urban areas can make sure the water quality meets the requirements of the EU bathing water directive. The technology can also be applied to water used for agricultural and landscape irrigation, and industrial water reuse applications such as disinfection of internal process water”, Bengt Hansen says.

The article was published in October 2017.