Small quantities with a big impact: micropollutants in wastewater can endanger entire ecosystems. A fourth treatment stage and ozone can render the problem substances harmless.

A considerable proportion of the pharmaceuticals that humans ingest pass through the body unchanged and are excreted in wastewater. These substances and other micropollutants are often insufficiently degraded in wastewater treatment plants. The conventional three treatment stages - mechanical, chemical and biological - are ineffective for many of them.

Pharmaceutical residues and leachate

Pharmaceutical residues enter streams and rivers with the treated water. There they can significantly impair the reproduction of many aquatic organisms and thus endanger entire ecosystems despite the very small quantities. More and more sewage treatment plants are, therefore, operating an additional purification stage to eliminate these substances. This can be achieved particularly efficiently with ozone.

In the 1990s ozone began to be used for wastewater treatment on a larger scale, including at landfill sites. Depending on the contents of the landfill, the leachate contains organic substances that are not biodegradable and pose a serious threat to the environment. For this reason, biological treatment of the leachate is often combined with an ozone stage.

Highly reactive oxygen molecule

Oxygen is a very reactive element. Its tendency to form chemical compounds is significantly increased in the case of triatomic ozone (O3) - compared to diatomic O2 from the air. The environmentally friendly molecule can break down a wide variety of organic substances very quickly, making them biodegradable.

In addition to the problematic pollutants in leachate, this also includes the micropollutants that have come under scrutiny: pharmaceuticals, pesticide residues and other critical chemicals. The directives of the EU and many countries now require effective additional measures over and above the three conventional treatment stages.

Method of choice

In Switzerland it has already been decided to install the fourth purification stage for large wastewater treatment plants. In the EU it is to be completed by 2035 with smaller plants being given a little more time to retrofit. It will probably also become standard in other regions in the future.

Ozonation is the method of choice for this fourth stage in most cases. It is as effective as it is efficient, and often cheaper than the possible alternatives. After contact with ozone, predominantly degradable reaction products remain. They can be easily removed from wastewater in the biologically active sand filtration.

Messer has extensive expertise in water treatment and supports sewage treatment plants in the implementation of ozone technologies. This begins with the construction of complete test plants for feasibility studies on a laboratory scale and extends to support for commissioning and the continuous supply of the required oxygen.

For more than 128 years, Messer, the today’s world's largest privately owned company for industrial gases, medical gases, specialty gases, and gases for electronics, committed to its guiding principles of safety, focus on customers and employees, responsibility for our society, sustainability, trust, and respect. Messer's Gases for Life and patented gas applications are essential for environmental protection, climate protection, decarbonization, and innovation.