These topics await you on this page:


Trickling filters are systems for biological wastewater treatment. They use bacteria and microorganisms that break down pollutants from the water, thus purifying the water. Even today, trickling filters are considered energy-efficient and low-maintenance – as long as modern materials are used and the latest design principles are applied. We do both and will be happy to assist you in designing your system.


Trickling filters are used in municipal and industrial wastewater treatment. Carbon removal, nitrification and denitrification can be achieved either simultaneously or with separate filters.


In trickling filters, the carrier material for the biofilm is permanently installed in the tank. The carrier material is sprinkled with wastewater from above.


The microorganisms in the trickling filter settle on different carrier materials forming a biofilm; therefore, trickling filters are classified as biofilm or trickle bed processes. In this field, our BIOdek® packings with cross and vertical structure have proven their worth in hundreds of equipped plants.

The microorganisms filter the pollutants from the wastewater and decompose them into their mineral components carbon, nitrogen and phosphorus. As a result, the microorganisms gain mass and energy.

The sprinkling is carried out by a rotary distributor, which ensures an even distribution of the wastewater on the trickling filter surface, which is open at the top. A distinction is made between distributor types with recoil drive, in which the outflowing wastewater moves the rotary distributor, and those with motor drive. The latter are controllable and the operator can thus monitor the cleaning performance and, at the same time, the effluent quality.

The microorganisms in the biofilm require oxygen to break down the contaminants contained in the wastewater. Air slots at the bottom of the tank allow air to flow in and aerate the biofilm via the resulting chimney effect.

The packings rest on a substructure designed to ensure aeration and unobstructed dripping of water from the packings.


Today’s modern trickling filters use structured plastic packings as biofilm carriers that are tailored to the application, for example our BIOdek® type.


We offer our BIOdek® packings in cross and vertical structures, which are often combined. For example, we use BIOdek® packings with vertical structure in upper layers of a pool, and those with cross structure in lower layers. By combining the best-suited BIOdek® types, we tailor the carrier material to the individual cleaning task. In doing so, we naturally also take static aspects into account. You can find out more about this in the “Static design” section.

Especially in regions where the energy supply fluctuates or where there is a lack of trained personnel, trickling filters have proven their worth for many years.

In older systems filled with stones or lava lumps, puddles form or they become clogged. This is a problem: the performance decreases. Today, we equip these trickling filters with our structured BIOdek® packings and maintain the performance of this plant over a long period of time. See an example of performance improvement after a trickling filter retrofit here.

Are you interested in retrofitting your trickling filter? Contact us!


Activated sludge plants are an alternative to trickling filters. In these plants, there are no fixed growth areas for a biofilm. Instead, so-called activated sludge flocs float freely in a basin filled with wastewater. They form because of extensive aeration and microorganisms within them ensure biological self-cleaning. To supply the microorganisms in the plant with sufficient oxygen, aeration systems are required that consume a lot of energy.

Trickling filters have the following advantages over activated sludge systems:

Lower energy consumption

Trickling filters do not need an aeration system, the oxygen demand is covered by natural convection. In addition, depending on the structural conditions, pumps can be saved by realizing the water feed by gravity. In this way, in municipal wastewater treatment plants, you can save costs of up to 70%.

No sludge recirculation necessary

In the trickling filter, the organisms are fixed in the biofilm, which prevents sludge from being flushed out. At the same time, this increases the so-called sludge age and thus leads to a higher performance of the trickling filter. The excess sludge only has to be separated, thickened and dewatered in the subsequent step of the process. Depending on the cleaning task to be performed by the trickling filter and the effluent values to be achieved, sludge recirculation can therefore be omitted.

More compact secondary sedimentation

Since the sludge settles better and generally less sludge is produced, the areas for secondary clarification and a possible recirculation can be kept smaller, which saves costs.

Robust process

Due to the structure of the biofilm, trickling filters are extremely robust against fluctuations in influent load. Therefore, sudden overloads or an inflow of toxic substances are much better absorbed and have only a minor effect on the effluent quality. Moreover, there is no problem with bulking sludge and its costly consequences in trickling filters.

Easy handling

The robust biofilm process in the trickling filter can be controlled simply and easily by regulating the water feed. To do this, you run the rotary distributor that sprinkles the packings faster or slower, adjusting the surface load and flushing intensity. In this way, you can easily control the process and operate the trickling filter even without highly qualified personnel.


We will be happy to design your trickling filter for you and take care of both the process and static design.

Design of the process

Our trickling filter design is based on algorithms developed in the Expoval research project of the BMBF (German Federal Ministry of Education and Research).

These new design principles consider not only the hydraulic parameters and the dirt loads, but also the climatic conditions at the installation site. This means that we can design the optimum trickling filter for any climate, whether cold or warm.

Take advantage of our know-how on the latest design principles. Contact us for your project – be it an upgrade or a new plant!

Static design

Equally important is the static design. This is because the biofilm and water generate high operating weights.

Based on customer data, we calculate both the substructure and the required weight classes of the packing. We adapt the BIOdek® packings to the different requirements in terms of both stability and surface structure.


The core of a trickling filter is the packings that act as the carrier material for the biofilm. Over 40 years we have acquired the know-how about the right materials, surface structures and use of the different types of packings, both for industrial and municipal plants. To ensure consistently high performance of the trickling filter, the other components such as rotary distributors must be adapted to it. Here, too, you can count on our support.

BIOdek® packings for your trickling filter

BIOdek® cross-structure packings are suitable for BOD5 degradation and nitrification.

Regardless of whether the wastewater is low, normal or high load, we have the appropriate media for your trickling filter due to the different specific surface area and slope angle of the channels. We can vary the film thicknesses to ensure the stability of the trickling filter.


You can find out more about BIOdek® tower packings with cross structure on our product pages.

Here you can find more information about our BIOdek® packing with vertical structure.

We recommend the use of BIOdek® packings made of polypropylene (PP) for trickling filters. They are – in contrast to filling material made of PVC – more environmentally friendly and easier to dispose of. We have compared PP and PVC materials for you. Find more information in our brochure GB-2H-Properties of Polymers. Contact us if you have any questions!

Denitrification in the trickling filter

To achieve a denitrifying effect in the trickling filter, we control the process to create anoxic conditions (anoxic = absence of free oxygen). As a result, we completely eliminate nitrogen from the wastewater.

The basis must be right: PIERdek substructure

Our PIERdek substructure is easy and quick to install, stable and robust. It is optimally matched to the BIOdek® packing and to the loads that occur, which are constantly changing due to the process. In this way, we ensure unhindered aeration and safe sludge discharge.

We statically design the substructure to carry the high weight loads generated by the water and the accumulating biomass. Depending on conditions, typical design loads range from 1000kg/m2 to 8000kg/m2 of floor area.

PIERdek is a prefabricated support system for trickling filter fill media and can be used in basins of any size and packing height. PIERdek consists of rigid supports made of PVC pipe with a lower base plate and a head plate on top. The base plate sits on a disc that can be used to compensate for ground slope (up to 5%). A grid system is fixed on the head plates with a 60% open area, which ensures aeration and sludge discharge.







Ofrecemos componentes y soluciones innovadores para procesos sostenibles en el campo del intercambio de calor, tratamiento de agua y aguas residuales e intercambio de materiales que protegen el medio ambiente. Nuestro equipo de profesionales trabaja para aumentar el rendimiento y la rentabilidad de su aplicación específica. Si necesita una solución a la medida…. Estamos a su disposición!