The presence of micro-pollutants from pharmaceuticals, cleaning agents, and personal care products in waterways poses a serious risk to both people and ecosystems. Conventional three-stage wastewater treatment plants are not designed to remove these contaminants, which is why a fourth stage of treatment is becoming increasingly essential in Europe and beyond.
The Challenge
ARA Thunersee, a major municipal treatment plant in Switzerland serving approximately 120,000 residents, required an advanced and reliable solution to address the growing issue of micro-pollutants. The plant turned to INVENT Umwelt- und Verfahrenstechnik AG, a trusted partner since 1996, known for its robust, energy-efficient mixing technology.
The Solution: PAC Process with HYPERCLASSIC®-Mixers
Since 2018, ARA Thunersee has operated the “Ulmer Verfahren” — a process using powdered activated carbon (PAC) in combination with coagulants and flocculants.
In this method:
- PAC is mixed with secondary-treated wastewater in a contact reactor.
- HYPERCLASSIC®-Mixers ensure intensive yet gentle mixing, promoting stable floc growth.
- Contaminant-loaded PAC flocs are then separated in sedimentation tanks and safely removed with waste sludge.
Why HYPERCLASSIC®?
The latest Evolution 7 HYPERCLASSIC®-Mixers deliver several performance advantages:
- High bottom velocities for efficient PAC suspension
- Low-shear mixing for gentle yet thorough floc growth
- Optimised homogenisation performance through advanced transport fin design
- Proven durability and low maintenance under demanding operating conditions
INVENT’s THINK Fluid Dynamix® division also provided computational fluid dynamics (CFD) analysis to determine the optimal placement of inlets, dosing points, and mixers — maximising efficiency and energy savings.
Results
Independent testing confirmed elimination rates of 81–95% for key indicator substances, well above the legal threshold of 80%. Even during heavy rainfall events, when partial bypasses occurred, the system maintained reliable performance and consistent treatment quality.
A Longstanding Partnership
ARA Thunersee has relied on INVENT’s mixing solutions for nearly three decades, beginning with twelve HYPERCLASSIC®-Mixers installed in the 1990s. The recent integration of Evolution 7 units reinforces the plant’s commitment to sustainable and future-proof wastewater treatment.
The ARA Thunersee project demonstrates how HYPERCLASSIC®-Mixers, combined with PAC adsorption technology, provide an effective and sustainable solution to one of the wastewater sector’s most pressing challenges, the elimination of micro-pollutants.