Cost-effective retrofit for denitrification tanks during ongoing operation at the wwtp Hagen-Boele
Following the insolvency of Kabel Premium Pulp & Paper GmbH, the Ruhrverband took over the paper mill’s wastewater treatment plant at Hagen-Boele, Germany. The plant was originally designed for wastewater from the paper industry and municipal wastewater and had to be converted at short notice to operate exclusively with municipal wastewater. This created the need to set up unventilated zones for denitrification in existing aeration tanks without interrupting plant operation for long periods or carrying out extensive structural modifications.
The plant has two large donut-shaped tanks, the outer ring of which is divided into several segments. For the new process control, some of these segments were to be operated as denitrification zones. The boundary conditions were challenging. Due to existing scraper bridges, only very limited installation space was available above the water level. There was considerable time pressure for implementation. Complete emptying of the tanks was out of the question for operational and economic reasons.
INVENT developed a suitable solution concept, which centered on the use of HYPERCLASSIC®-Mixers in combination with steel bridges adapted to the specific plant. The vertical design of the mixers and the compact drive design allowed them to be installed under the existing scraper bridges without impairing their function. At the same time, the mixers could be aligned in such a way that accessibility and operational safety were guaranteed under the cramped space conditions.
The steel bridges were the second central element of the concept. They were designed to rest on existing structural elements and could be installed without extensive modifications to the con , concrete, or basin walls. This eliminated the need for costly preparatory work and significantly reduced installation time at the plant. In addition, open side brackets were provided to accommodate the mixers. In combination with the HYPERCLASSIC®-Mixers, this bridge concept enabled complete installation in the filled basin. The load was transferred and assembly carried out via existing structures, incorporating the existing scraper bridge. For the operator, this meant rapid implementation with manageable project costs.
With their characteristic geometry, the HYPERCLASSIC®-Mixers ensure uniform flow distribution and reliable suspension of the activated sludge at a comparatively low power density. Especially in denitrification zones, stable mixing without air ingress is crucial for process reliability.
The INVENT solution at a glance:
- Fast and cost-efficient retrofit, without new construction and without downtime of the basins
- Installation in filled basins, made possible by steel bridges and vertical hyperboloid mixers
- High energy efficiency with reliable denitrification, low power density with high circulation capacity
- Optimized for donut tanks and confined installation situations, even under existing scraper bridges
- Operator-friendly and future-proof, suitable for municipal requirements and stricter discharge values from 2026
The Hagen-Boele project exemplifies that stable denitrification will remain a central element of municipal wastewater treatment in 2026, especially when taking over and converting existing plants. At the same time, it illustrates how intelligent concepts can be used to continue using existing tanks in the short term and adapt them to new operational requirements without new construction or lengthy downtimes.
