Germany's pioneering role in the fourth treatment stage: More and more wastewater treatment plants are relying on HUBER’s proven technology modules

Germany's pioneering role in the fourth treatment stage: More and more wastewater treatment plants are relying on HUBER’s proven technology modules

It has been in force since 1 January 2025 – the new EU Urban Wastewater Treatment Directive (UWWD). One of the key points is the comprehensive introduction of the fourth treatment stage in Europe. This affects all wastewater treatment plants larger than 150,000 PE and larger than 10,000 PE in sensitive areas, which must be defined by the member states by the end of 2030.

Germany, above all Baden-Württemberg, has taken on an important pioneering role here and has already expanded a number of wastewater treatment plants with a fourth treatment stage in recent years. Many of these first large-scale pioneer plants rely on the proven technology modules from HUBER.

Fourth treatment stage of Westerheim WWTP already in operation since 2015

The Westerheim WWTP in the Swabian Alb, for example, was one of the first wastewater treatment plants in Germany to be equipped with a fourth treatment stage in 2015. There, the two HUBER Sandfilter CONTIFLOW® protect the downstream activated carbon stage from dirt and impurities.

Lonsee: Pre-filtration is also flocculation filtration

The fourth treatment stage at the Lonsee/Halzhausen wastewater treatment plant has also been in operation since 2020. As in Westerheim, a total of 6 HUBER Sandfilter CONTIFLOW® provide reliable pre-filtration upstream of the activated carbon stage, while also performing the function of flocculation filtration for phosphorus elimination.

Uhldingen-Mühlhofen WWTP: 24 HUBER Active Carbon Filter CONTIFLOW® GAK

Germany's largest process combination of ozonation and activated carbon filtration to date was put into operation at the Uhldingen-Mühlhofen wastewater treatment plant in 2023. HUBER supplied the activated carbon stage with a total of 24 HUBER Active Carbon Filter CONTIFLOW® GAK units for biological post-filtration and adsorption. In addition, the proven HUBER Pressure-Tight Door TT7 was delivered for the ozone reactor.

In 2024, the Uhldingen-Mühlhofen wastewater treatment plant discharged over 6.5 million m³ of treated wastewater into Lake Überlingen. This part of Lake Constance supplies around four million people in large parts of Baden-Württemberg with about 135 million m³ of drinking water annually.

Bickenbach WWTP: Hesse's most modern fourth treatment stage

Bickenbach also opted for the combined process of ozonation and activated carbon filtration and successfully put it into operation in April 2025. 

Together with the upstream cloth filtration, it is currently the most modern fourth treatment stage in Hesse, according to the operator.

Still remarkably high elimination performance in the fifth year of operation

The Fridingen wastewater treatment plant with its connected 5,300 PE is probably the smallest wastewater treatment plant in Germany that has been equipped with a large-scale fourth treatment stage to date.

It was commissioned in 2020 and consists of two HUBER Active Carbon Filter CONTIFLOW® GAK 72, which treat around 700 m³ of wastewater per day.

After four years of operation, a very high elimination performance of 88% was still achieved in November 2024, which is why there is no need to think about replacing the activated carbon in the near future.

Especially for smaller wastewater treatment plants such as Fridingen, the activated carbon process is ideal as a fourth treatment stage. The activated carbon filters can be easily retrofitted and do not require any complex carbon dosing technology. In contrast to powdered activated carbon, granulated activated carbon can also be reactivated and then largely reused, which means significant cost savings for operators such as the municipality of Fridingen.