It has been known for some years that there are substances in our waters and wastewater that can only be removed to a minor extent or not at all during wastewater treatment in the municipal wastewater treatment plant. We are talking about anthropogenic trace substances or micropollutants.

What are micropollutants?

Micropollutants are synthetically produced, non-natural microcontaminants found in minute concentrations of billionths (nano) to millionths (micro) grams per liter.

From the chemical point of view, the term "micropollutants" covers all synthetically produced organic-chemical compounds that are released into the environment.

In environmental science, and especially in the wastewater sector and engineering, the term micropollutants is used to distinguish dissolved substances from viscous and insoluble (particulate) compounds.

What types of pollutants are there?

From a purely chemical point of view, each compound has a specific reaction mode in water, is either completely or partially degraded, transformed or leaves the three purification stages of a wastewater treatment plant unhindered, for example, and re-enters the ecosystem.

These substances include compounds such as pharmaceuticals, drug residues, pesticides, and also per- and polyfluorinated compounds such as PFAS (or PFC) as well as soluble polymers, known as micropollutants, but also inorganic substances such as heavy metals, phosphates, and sting compounds, as well as the pollutant class microplastics

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, not only the chemical and physical properties but also the combined environmental properties are considered and the (eco-)toxicological influences are determined as a function of the environmental factors (persistence, degradability, etc.).

The dilution factor generally lowers the (eco-)toxicological impact, the substances are then considered to have reduced (eco-)toxicological relevance. In recent years, however, an increasing number of micro-pollutants have been detected in the water cycle, which are known to cause lasting disturbance to the ecosystem.

Micropollutants and the fourth treatment stage in municipal wastewater treatment plants

Due to the fact that many micropollutants can pass unhindered through the three treatment stages of a municipal wastewater treatment plant, there is a growing desire for an additional fourth treatment stage for centralized wastewater treatment, which would take care of precisely those substances that could not be removed before, but are potentially classified as hazardous.

The requirements for this fourth purification stage are complex. With the state of the art and minor adjustments, the limit of the purification performance is very often reached more quickly. On the one hand, the purification 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, which arise, for example, from chemical or biological conversions, or to make them manageable for the wastewater treatment plant operator.

In addition, the fourth cleaning stage must be easy to operate for trained personnel and must be integrable into an existing plant. An appropriate, justifiable, cost/benefit factor must be taken as a basis.

What are the processes for micropollutant removal in wastewater treatment plants?

All processes can be combined with one another, but it is important to bear in mind that each has limiting factors that cannot be completely eliminated even by combining two process approaches. Examples of process-related limitations are

  • the uncertainty about by-products in oxidative processes,
  • slippage and desorption of powdered activated carbon,
  • high consumption of chemical additives,
  • high maintenance costs,
  • personnel and/or space capacity.

High investment costs, due to the construction effort, are also  limiting factors for wastewater treatment plants with less favorable framework conditions. 

More news in our blog

16. April 2024

EU Urban Wastewater Directive adopted in April

The EU Urban Wastewater Directive (UWWTD for short) was adopted by the European Parliament at the beginning of April 2024. Among other things, it aims to remove microplastics and micropollutants from our wastewater and increase the efficiency of wastewater treatment plants in a cost-effective manner. The keywords here are also: Resource conservation, water quality, circular economy, energy efficiency and sustainability. But what is the roadmap for this? We have taken the Wasser 3.0 perspective.
8. April 2024

Our blog about water without microplastics

We want to stop the uncontrolled pollution of our water with microplastics and micropollutants. In our blog posts, we describe step by step why it is high time to do so and how we want to achieve this. We focus on current information and always keep an eye on the latest opinions and curiosities.
1. April 2024

Sustainable education and knowledge transfer

On the trail of the WHY.... The world is becoming ever more dynamic. The role and function of education and training (school, work, everyday life) is becoming increasingly important. The aim is to offer complexity-reducing transfer tasks and provide assistance in order to be able to argue and act on the basis of facts in the search for answers to pressing questions. This is all quite complex and requires some optimization and adaptation. A look behind the scenes of WASoMI.