Flagship project in Upper Austria: Ecological reed bed sludge treatment at the Polling wastewater treatment plant

This is another way to treat and dewater sewage sludge: using the natural, biological process of reed bed sludge treatment. A sustainable showcase project is being created in Polling im Innkreis – also because two wastewater treatment plants are being merged.

Combining technology and ecology

With the comprehensive reconstruction and expansion of the Polling wastewater treatment plant, one of the most significant wastewater projects in the region is currently being developed. It combines technical innovation, sustainability and regional cooperation.

The ecological and functional centerpiece of the facility is the near-natural treatment of sewage sludge using reed bed drying and stabilization basins. This process will significantly shape the plant’s future operation.

Merger conserves resources and reduces costs

The project is based on a major reconstruction scheduled for completion by 2027: The wastewater treatment plant of the water protection association Kobernaußerwald (4,800 population equivalents) in the municipality of Lohnsburg will largely be dismantled. In future, wastewater treatment will be carried out exclusively in Polling (currently 6,300 population equivalents), with the expanded facility designed to handle 12,500 population equivalents (PE). This ensures that the wastewater treatment plant is dimensioned for long-term future requirements.

The existing infrastructure will be consolidated through the merger of the two plants. The benefits include greater operational reliability, more efficient processes, centralized monitoring and control, as well as significantly improved treatment performance.

Sewage sludge treatment using reed bed stabilization

The core element of the facility is reed bed sludge treatment, a completely biological treatment process.

In large basins, reeds (Phragmites australis) grow through the liquid sewage sludge without any additives and absorb water. Most of the water evaporates through the plants, while the remaining water drains away through drainage systems at the bottom of the basin. This reduces the volume of wet sludge by up to 98 percent!

The oxygen introduced through the plant roots supports the biological decomposition of the sludge. After 8 to 15 years – depending on the system design and sludge quantities – the basins are mechanically emptied. The nutrient-rich soil produced is used as humus in agriculture.

Fully ecological: The benefits of reed bed sludge treatment

Reed bed sludge treatment relies exclusively on natural processes:

• Root penetration of the sludge by reed plants

• Continuous dewatering through evaporation and transpiration

• Oxygen input into the sludge layers

• Promotion of microbiological degradation processes in the root zone

• Long-term stabilization and mineralization of the sludge

The sludge volume, and therefore the effort required for disposal, are significantly reduced. At the same time, the system operates virtually without odors, requires minimal energy input and therefore causes lower CO₂ emissions. It also integrates naturally into the surrounding environment.

Donau Chemie provides expertise on ecological processes

Donau Chemie Water Technology has been supplying the Polling wastewater treatment plant with the flocculant and precipitant Donau Klar for many years. The responsible account manager Rudolf Bauer says:

“Sustainability is a major priority for this customer, and we fully support this commitment; it is something we clearly understand. That is why Donau Chemie operates Carinthia’s largest photovoltaic system and has been using hydropower for energy generation at most of our plants for decades.”

Donau Chemie also supported the merger of the two wastewater treatment plants, for example by carrying out hydrogen sulfide measurements in the pipelines during the reconstruction work.

Conclusion: Expansion of sustainable sewage sludge treatment

As part of the reconstruction, sewage sludge treatment using reed bed stabilization basins will be specifically expanded. An additional basin with an operating area of around 2,000 m² will increase the plant’s capacity and ensure its long-term performance even as requirements continue to grow.

With an investment volume of around five million euros, this represents the largest investment project to date by the water protection association Polling.

The combination of modern technology and natural biological processes demonstrates how infrastructure can be designed in a sustainable, resource-efficient and future-oriented way. The Polling wastewater treatment plant is therefore becoming a showcase project for ecological wastewater treatment in Upper Austria.