Sometimes, a successful project begins by looking beyond district boundaries. When the municipality of Grebenhain in Germany was searching for a solution to meet the increasing demands placed on the pond wastewater treatment plant in the village of Bannerod, its attention was drawn to an existing fixed-bed reactor installation in Schrecksbach, located in the neighboring Schwalm-Eder district. The results achieved there demonstrated that modern upgrades to existing treatment plants can provide an economical and sustainable alternative to extensive new construction projects or costly sewer infrastructure expansions.
To explore the possibilities for Bannerod in greater detail, the municipality approached PPU Umwelttechnik. During a municipal council meeting, we presented our fixed-bed reactor process and explained how the existing pond treatment plant could be future-proofed through the addition of an extra biological treatment stage. Of particular importance was the question of whether the technology would perform reliably under the specific conditions at the site.
For this reason, wastewater samples were collected from the Bannerod treatment plant and analysed as part of a feasibility study under realistic operating conditions. The results clearly demonstrated that ClearFox® fixed-bed reactor technology would be capable of achieving the required treatment performance while sustainably relieving the load on the existing plant. This established the technical basis for moving the project forward.
Following this, the municipality of Grebenhain conducted a formal public procurement procedure. PPU Umwelttechnik participated in the tender and was awarded the contract after completion of the procurement process. Today, the new containerized solution ensures that the existing pond treatment plant can continue to operate reliably even under changing conditions – a project that has since attracted attention beyond the municipality itself.
The successful implementation of the project has also received coverage in the regional press. The following article reports on the modernization of the Bannerod wastewater treatment plant and demonstrates how existing pond treatment systems can be upgraded economically and sustainably to meet new requirements.
New Technology for Pond Wastewater Treatment Plants
Modular Container-Based Solution in Bannerod Sets an Example for the Vogelsberg District
13 May 2026
Bannerod – The small village of Bannerod, part of the municipality of Grebenhain, is now home to a wastewater treatment plant that serves as a model for the entire Vogelsberg district. Remarkably, this is not a newly built facility but rather the modernization of an existing pond treatment plant that originally went into operation exactly 40 years ago. The modern technology is housed discreetly inside two container modules and consists of a so-called fixed-bed biological reactor system. On Monday, Mayor Simon Seibert, Wastewater Manager Andreas Jost, Public Works Manager Wolfram Mohr, Jürgen Steuber from the Lower Water Authority of the Vogelsberg district, and Quirin Döhler from Bayreuth-based PPU Umwelttechnik visited the site to see the upgraded facility for themselves.
“For us, it was important to find a solution that is technically reliable, economically viable, and improves the protection of the Lüder River,” said Wastewater Manager Jost. “With this modular retrofit, we have been able to preserve the existing facility while significantly enhancing its treatment performance.”
As an aerated pond treatment plant, the facility in Bannerod represented a type of technology that is frequently found in small municipal wastewater treatment systems—fewer than 120 people live in the village. However, this type of technology is increasingly reaching its limits under changing operating conditions. In Bannerod, this became particularly apparent during prolonged periods of dry weather, when reduced water volumes and higher pollutant concentrations made it more difficult to consistently comply with the required discharge limits, especially for ammonium, before releasing the treated water into the Lüder River. In recent years, these values repeatedly exceeded the permissible thresholds. In addition, the polishing pond was at risk of biological instability during extended dry periods.
Rather than undertaking a complete reconstruction of the wastewater treatment plant or constructing a pressure sewer pipeline—both large-scale projects requiring lengthy planning processes—the municipality of Grebenhain decided, after evaluating various alternatives, to implement a compact modular container solution. This technology adds an additional biological treatment stage. In the so-called submerged fixed-bed process, the microorganisms required for wastewater treatment colonize the fixed media inside the container. The new ClearFox® FBBR system is capable not only of enhancing the existing treatment performance but also of taking over nearly the entire treatment process. As a result, the old pond treatment plant is significantly relieved of its workload and will primarily serve as an equalization basin in the future. Less than one year passed between the evaluation of potential solutions and the technical implementation of the project.
The cost of upgrading the Bannerod wastewater treatment plant amounted to less than €200,000. “We were able to stay within the targeted budget,” emphasized Mohr. “The major advantage is that these containers can also be relocated to another site if required. That gives us a great deal of flexibility,” explained Mayor Seibert, noting that the two container modules could be moved to another location within the municipality if necessary. Considering that the municipality of Grebenhain is responsible for maintaining eight wastewater treatment plants, four pumping stations, and 92 kilometres of sewer network, this flexibility also represents a significant economic advantage, as Jost added. “The reference project in the neighbouring district has delivered positive results,” said Steuber, expressing his hope that this first containerized wastewater treatment plant in the Vogelsberg district will perform just as successfully as the installation already implemented in Schrecksbach in the Schwalm-Eder district.
© Carsten Eigner
The project in Bannerod serves as an excellent example of how existing municipal wastewater treatment plants can be adapted to meet new requirements with comparatively modest investment. Thanks to its modular design, the technology can be deployed flexibly and even relocated to other sites if required. We would like to thank the municipality of Grebenhain for the trust they placed in us throughout the project and are delighted that the facility is now contributing to the long-term, sustainable treatment of wastewater in the region.
