In 2024, a small community in Hesse with around 1,000 inhabitants faced a challenge typical of many pond-based wastewater treatment plants: following the partial renovation of the sewer network, the inflow conditions changed so significantly that it was no longer possible to reliably comply with the official discharge limits. Provisional measures – such as floating aerators – fell short of expectations: too little effect, too low energy efficiency and no robust reduction in nitrogen and phosphate loads.
The municipality therefore looked for a solution that could be quickly integrated, was space-saving and reliable – without completely rebuilding the existing pond treatment plant. This is exactly where containerised sewage treatment plants come into their own: they are delivered pre-assembled, are modularly scalable and require only a small footprint. The approach has proven itself in practice because it offers short installation times, predictable costs and a defined performance chain – from the biological stage to secondary clarification and phosphate precipitation.
Pond treatment plants are sensitive to fluctuations in load and hydraulic peaks. If receiving water or discharge limits are tightened, they quickly reach their limits without targeted retrofitting – especially in terms of nitrification (ammonium reduction) and phosphorus reduction. At the same time, space is often limited on site, and a complete new build is hardly economically feasible for small communities.
Phosphorus is particularly critical: increasing water protection targets and regional requirements necessitate reliable reduction. In Germany, chemical phosphate precipitation with iron or aluminium salts is an established standard because it is robust and works independently of temperature fluctuations. Studies confirm the widespread use of such precipitation agents in municipal sewage treatment plants – an indication of the maturity and practicability of the process.
The same applies to solid-liquid separation: traditional secondary clarifiers require space and favourable flow conditions. Lamella clarifiers use inclined plates to create a large effective settling area in a small space, thus increasing the power density – ideal for compact retrofits or confined locations.
The municipality opted for a ClearFox® container sewage treatment plant from PPU Umwelttechnik GmbH – a compact, efficient retrofit between the storage pond and the second treatment pond. The wastewater is extracted from a pump shaft and passes through two 20-foot containers with clearly structured process technology:
Biological stage – fixed bed process in three cascades
PPU Umwelttechnik GmbH opted for a fixed bed reactor for biological treatment. The reactor line is divided into three zones connected in series; the carrier material gradually increases in specific surface area from 100 to 150 to 200 m²/m³. Microorganisms settle on these surfaces as biofilm and ensure the degradation of organic substances and reliable nitrification. The advantage of the fixed bed: the biofilm stabilises the process against load and temperature changes, is energy-efficient and can be precisely adjusted via aeration times and hydraulic load. Detached biomass (secondary sludge) is safely removed in the next stage.
Secondary clarification – lamella clarifier with sludge recirculation
Solid-liquid separation is performed by a lamella clarifier. The inclined plates increase the settling area in a compact design, resulting in short retention times, clear effluent values and a small footprint. The settled excess sludge is returned to the primary clarifier. Lamella technology is particularly effective in retrofit situations because it exceeds the performance of conventional tanks in confined spaces.
Phosphate precipitation – integrated dosing
For phosphorus removal, we dose precipitating agents from an integrated IBC tank directly into the clarification stage. The combination of biological treatment and chemical precipitation reliably achieves low P values in the effluent, even with fluctuating inflows. In Germany, this approach is state of the art and contributes significantly to water protection.
Automation & energy
The control and ventilation technology is fully integrated into the container. This reduces the number of interfaces on site, simplifies commissioning and enables finely scalable operating strategies. Thanks to pre-assembled modules, installation time is short, quality is high and documentation is standardised.
Integration into the existing system
Hydraulically, the system is integrated as a bypass/booster stage between the storage pond and the second clarification pond. The treated water then flows back into the second pond. The process stabilises the entire system and reduces loads in the long term.
Service from a single source
PPU took care of planning, production, installation and commissioning – turnkey, on time and within budget. Whether upgrading a pond treatment plant, providing a temporary solution or permanently expanding capacity, PPU Umwelttechnik GmbH supplies turnkey containerised treatment plants with a clear performance guarantee. Contact us. We will analyse your current situation, define target values and design the appropriate module configuration for your location.
In most cases: yes.
Container sewage treatment plants are modular in design and can be adapted to different population equivalents, inflow volumes, pollutant loads and structural conditions. Whether you have a pond treatment plant, activated sludge process or mixed system, we configure the modules to fit into your existing plant system.
All you need is:
• a stable surface as a place to install it,
• electricity and water connections,
• connection to the existing sewage system.
Everything else, such as ventilation, control, electrical systems and process automation, is already integrated into the container.
Microorganisms colonise special carrier materials in the fixed bed reactor. This biofilm breaks down pollutants, ammonium and organic matter. The process is particularly robust, temperature-stable and reacts flexibly to load fluctuations – ideal for municipal and industrial applications.
Yes, these systems were developed precisely for this purpose. The modules can be integrated as:
• an additional stage,
• a bypass solution,
• a nitrification/denitrification stage,
• a P precipitation stage or
• a temporary replacement system
– depending on your requirements.
Most likely, yes.
Since the modules can be retrofitted and expanded, additional containers can be added, e.g. for further nitrification, P elimination or filtration. The system offers long-term planning security – even with new limit values or changed inflows.
