Micropollutants in our waters

For several years it has been known that there are substances in our waters and wastewater that can only be removed slightly or not at all during wastewater treatment in the municipal sewage treatment plant. We are talking about anthropogenic trace substances or micropollutants.

What are micropollutants?

Micropollutants are synthetically produced, non-natural micropollutants, which are found in the smallest concentrations of billionths (nano) to millionths (micro) of a gram per liter. They include substances such as pharmaceuticals, pesticides, PFAS (PFC) and microplastics. A distinction is made between the totality of organic-chemical loads in dissolved and undissolved or insoluble organic-chemical compounds. Every compound has a certain type of reaction in water, is either completely or partially degraded, converted or leaves unhindered, e.g. the three purification stages of a sewage treatment plant and gets back into the ecosystem.

Micropollutants and environmental relevance

In order to be able to make a qualified statement about the behavior of these contaminants in the environment and their environmental relevance, one considers not only the chemical and physical but also the combined environmental properties and determines the (eco) toxicological influences depending on the environmental factors (persistence, degradability, etc.).

The dilution factor generally lowers the (eco) toxicological influence, the substances are then considered to be of reduced (eco) toxicological relevance. In recent years, however, more and more micropollutants have been detected in the water cycle, which are known to have a lasting effect on the ecosystem.

Micropollutants in wastewater treatment

For some years it is known that there are materials in wastewater, which can be removed only to a certain extent or not at all during wastewater treatment in municipal sewage plants. We are talking about anthropogenic trace substances or micropollutants. Micropollutants are synthetically produced, non-natural micro contaminations, which are found in smallest concentrations of millionth (micro) to billionth (nano) gram per liter.

They are comprised of substances such as pharmaceuticals, pesticides, but also microplastics. The totality of organic-chemical pollution can be divided into dissolved and undissolved or insoluble organic-chemical compounds. In water, each compound shows a specific type of reaction: it is either completely, partially or not at all degraded or converted.

That means, in parts micropollutants leave unhindered e.g. the three purification stages of a wastewater treatment plant and enter the ecosystem.

Micropollutants and the fourth purification stage in municipal sewage treatment plants

Because many micropollutants can pass through the three purification stages of a municipal sewage treatment plant unhindered, the desire for an additional fourth purification stage for the central wastewater remediation is louder, which should take care of exactly those substances that could not be removed before, but are potentially classified as dangerous.

The requirements for this fourth cleaning stage are complex. With the state of the art and minor adjustments, you can very often reach the limit of the cleaning performance faster.

On the one hand, the cleaning stage must be able to remove a wide range of problematic substances, the micropollutants, to a large extent. On the other hand, it is also important to avoid undesirable by-products, for example through chemical or biological conversions, or to make them controllable for the sewage treatment plant operator.

In addition, the fourth cleaning or purification stage must be easy to operate for trained personnel and it must be possible to integrate it into an existing system. An appropriate, justifiable, cost / benefit factor must be used.
Procedure for the elimination of micropollutants

Now, various methods for removing micropollutants, the so-called micropollutant elimination, are available. These can be divided into four groups based on their respective mechanisms of action: adsorptive, biological, oxidative, and physical.

All processes can be combined with one another, but it must be considered that each of them has limiting factors, which cannot be eliminated even by combining two process approaches.
Examples of procedural limits are:

  • the uncertainty about by-products in oxidative processes,
  • slip and desorption of powder activated carbon,
  • high consumption of chemical auxiliaries,
  • high maintenance costs,
  • personnel and / or spatial capacity.
High investment costs due to the structural effort are also limiting factors for sewage treatment plants with less favorable framework conditions.
Within the current research and development work in our remove area, we are concerned with solutions for the simultaneous removal of microplastics and micropollutants. The area of application is, among other things, the fourth cleaning stage in sewage treatment plants.