Below you will find answers to the main questions about our electroless small wastewater treatment plant ClearFox® nature. Please contact us for further information. We’re here to help!

Fully biological wastewater treatment plant without electricity

What sizes are available?

ClearFox® nature is a small wastewater treatment plant (wastewater inflow up to 8 m³/d). Our standard sizes are 4 p.e. and 8 p.e.. Extensions are possible with parallel operation units.

How does ClearFox ® nature work?

ClearFox® nature is an electricless biofilm system with filter effect. It runs without any input of electrical power. It consists of a mechanical pre-treatment and a subsequent biological treatment (biofilm reactor). The raw wastewater passes first the pre-treatment tank. The pre-treatment tank works as buffer tank, settling tank and sludge storage. The solid substances (e.g. toilet paper) settle there.

The settled substances will be compressed and stored. The daily fluctuations of the inflow can be equalised. The water flows through the system by itself (by gravity), pumps are not necessary. Between the pre-treatment and the biofilm reactor a mechanical throttle is installed to equalise the inflow.

The mechanically pre-treated wastewater enters the bioreactor, where it is poured gush using a tippling device. It impinges on perforated distribution boxes and drops evenly through the holes into the biological treatment part.

The biological treatment is done by bacteria that are naturally found in sewage. The cleaning process is the same as it takes place in rivers and streams – only intensified. For this, the bacteria need optimal conditions to reproduce. Therefore various high surface area materials for settling and growth of bacteria (biofilm) are put into the biofilm reactor. In addition, the bacteria need oxygen. They uptake the oxygen out of the air that automatically flows into the tank. The air flows by itself through the system of holes in the cover of the bioreactor and a vent pipe forced by a chimney effect. Inside the bioreactor the air is evenly distributed by a hollow body sytem.

While cleaning the wastewater the bacteria produce sludge. The sludge will remain in the bioreactor and even partially self-consumed by the bacteria, so except residues no further sludge is discharged. In contrary to other systems this system does not need any secondary settling tank. Residual minimal amounts of particulate matter, as permitted in accordance with DIN EN 12566-3, are discharged via the drain.

Which components do the cleaning work in the bioreactor?

In the bioreactor different types of packing are installed: Biofilm growth support media and ventilation elements. The biofilm growth media differ in such made of rough material with a high specific surface and coarsely structured, plastically constructed bodies. They have large surfaces. The bacteria that purify the wastewater attach themselves there and grow to a biofilm.

Why does ClearFox® nature work without energy?

The waste water flows through the system by gravity, that means that it flows under the force of gravity and is distributed. Ventilation takes place in a natural way, the circulation ensues automatically in the bioreactor (chimney effect).

What happens if not enough slope exists?

If there is not enough slope and the treated water cannot be discharged by gravity a little, low-current pump can be installed. The pump can also be powered by a solar panel.

How works the ventilation?

For ClearFox® nature its own ventilation system was developed. It consists of a ventilation tube that extends ≥ 1m above the ground level and the ventilation media inside the bioreactor. The plant is completely ventilated taking advantage of the chimney effect. The air flows predominantly from the top through the holes in the cover and will be evenly distributed in the whole bioreactor and leaves the system via the ventilation pipe. All sites are sufficiently ventilated.

What will happen if too much or too little water flows in?

The people vary in a household. Visitors, celebrations, but also children who come only on weekends change water consumption. For variations of waste water, the same applies as for fluctuating concentrations. The throttle equalises and ensures a balanced feed. See also “How reacts ClearFox® nature to concentration peaks and minimum of concentration?”

In which group of small wastewater treatment plants ClearFox® nature should be categorised?

ClearFox® nature is a cascaded biofilm plant with filtration effect. The wastewater flux in the bioreactor is vertically.

What distinguishes ClearFox® nature of soil body filtering systems (BKF)?

ClearFox® nature is an outstanding and compact wastewater treatment plant. It has been created based on many years of investigation. Parallels to BKF which has been highly reliable since more than 15 years can be drawn to the effect that essential components also can be found in ClearFox® nature. However the aim of BKF was and is only to treat the wastewater. There is no limitation of space required for BKF. Mechanisms such as cascading, or setting an equilibrium state during loading were taken up and developed.

ClearFox® nature represents a development of the original BKF concept, but with a different aspect:

  • Compactness
  • Traceable calculation bases
  • Exactly adapted special growth carrier
  • Defined cascade
  • Filtration effect as a benefit
  • Endogenous sludge consumption

How does ClearFox® nature react to concentration peaks / minima?

Nutrient concentrations in the waste water can vary from day to day, but also during the day. Purification generally works best if the concentrations are balanced. The bacteria that absorb the nutrients from the wastewater as food and thus purify the water are oversupplied with concentration peaks and starve and die in extreme cases when concentration minima appear.

Therefore a throttle between the primary treatment and the biofilm reactor where the main treatment takes place has been installed. This ensures that the nutrients are added to the bioreactor evenly throughout the day. The results of the practical test according to DIN EN 12566-3 confirm that the cleaning performance of ClearFox® nature is virtually independent of supply fluctuations.

How can be saved most costs in comparison with other treatment systems?

The operating costs are very low. There are no costs of energy (operation and fault messages of the installed equipment), spare parts (controller, aerators, compressors, solenoid valves, pumps, membranes, etc., as well as exchange of work) and secondary sludge removal as of conventional systems using ClearFox® nature at all! The operating costs for ClearFox® nature consist only of the reduced primary sludge removal from the primary sedimentation and the maintenance required by law (applies to all KKA).

Moreover, the volume of the primary sludge is lower than other systems and therefore has to be removed less often. Previous flowing, oxygenated water or mud from the biological part, hindering the settling, will not occur at ClearFox® nature. The primary sludge can settle optimally and rot and is more compact.

What must be done during maintenance?

Compared to technical small wastewater treatment very little has to be done. The control of a wastewater treatment plant is divided into the operator control and maintenance by an external, certified maintenance company. Detailed instructions are provided in the operating manual. In general, both the control of the operator and the maintenance because of the construction are very simple in ClearFox® nature.

It lacks any failure-prone, electronic components and sludge has to be removed more seldom. The maintenance is simplified and shortened – and therefore cheaper – because, for example, no time-consuming sludge volume (SV30) must be measured, and no technical wear parts are replaced.

Can ClearFox® nature applied to other than domestic sewage?

Basically ‘yes’. In particular, the high proven stability of the biofilm system for complex wastewater compositions and even toxic materials allows an application for different types of wastewater. In that case a project-specific adaptation of the design has to be considered..

What happens if the inflow is too high?

Then the emergency overflow starts. An overflow of the whole treatment plant will not happen.

What are the operating costs?

The operating costs are comparatively low. Detailed Information on this is the cost comparison at

How long can the holiday period last (no sewage inflow)?

In contrary to e.g. SBR systems ClearFox® nature regulates itself due to the biofilm technology, automatically by a kind of hibernation. By designing the filler remains without waste water supply always a residual moisture content in the nutrient-rich biofilm and thus active microorganisms in a bioreactor.

Just as an example may be mentioned a pilot plant, that was put out of operation during winter time from December to May. After the 5-month period it could immediately put back into operation without break-in. However, the bacteria are not immortal as a living being. As in nature arises here a balance between the number of organisms and the food supply.

Only the speed of their reduction (buffer effect and moisture content in the plant) may be extended. In practice, it can be considered of about 4 weeks.

How long is the break-in?

The training period (nursery of microorganisms) corresponds to that of other comparable biofilm systems (such as the soil body filtering system BKF) and is usually longer than in submerged principles (for example SBR, activated sludge plants). Depending on the season (outside temperatures!) can be expected 5-7 months.

The system however works immediately after start-up and achieves a partial purification. Due to the specially developed packing immediately physical / chemical treatment of waste water (mainly by adsorption) takes place. The microorganisms also begin their purification activities from the date of the first wastewater supply.

To speed up the growth of the biofilm (bacterial adhesion and colonization thickness) an adjuvant may be added (accessories PPU Umwelttechnik GmbH).

What is meant by areas with high and low nutrient supply and periods with high and low nutrient supply?

During the fluctuation of the daily/weekly/monthly wastewater inflow and concentrations different phases appear (maxima in the morning, noon and evening; minimum at night). Different zones are formed inside the bioreactor by the cascaded arrangement of the packing. Nutrient rich areas and periods are such with a high delivery of nutrients. There mainly degradation of carbon compounds and nitrification happens.

Nutrient poor areas and periods are such with a low delivery of nutrients. There mainly also nitrification and aerobic sludge consumption occurs.

What is aerobic sludge consumption?

Wastewater purifying bacteria produce sludge. Most of the small wastewater treatment systems need a secondary treatment after the biological treatment to remove the solids and sludge from the purified water. This process needs a additional tank and pump. Also the sludge has to be disposed.

In other systems the solids and the sludge remain in the treatment system. These are filtration system. Disadvantage of such systems is the possibility of blocking. The filter material has to be regularly replaced.

ClearFox® nature however uses the process of aerobic sludge consumtion.

With a sufficiently long residence time of the wastewater and sludge ( “sludge age”) in the bioreactor, not only the nutrient content is reduced in the wastewater, but even the resulting sludge will be “eaten” from the bacteria using oxygen, to reach a substantial mineralisation. In fully mixed reactors only a stabilization of the sludge takes place when the freely available carbon is completely consumed. Stable means that the sludge is no longer biologically active, so it cannot be further degraded.

ClearFox® nature uses a cascading of wastewater treatment. The processes of reduction of carbon compounds, nitrification and aerobic sludge stabilisation run in vertical sequence in separated areas. Mainly in the lower parts occur nutrient poor zones. Additionally, nutrient poor areas and periods arise in the inner sections of the hollow bodies in the bioreactor.

Benefits of the aerobic sludge consumption at ClearFox® nature are:

  • No accumulation of secondary sludge
  • No secondary clarifier or tank
  • No material replacement due to filtration
  • Lower costs

Is it necessary to replace the packing inside the bioreactor?

ClearFox® nature is a biofilm treatment system with means of filtration. The bodies for the adsorption and growth of the biofilm is permeable. The filtration action is minimised (see also the chapter concerning aerobic sludge consumption). If blocking occurs in contrary to the expected behaviour it can easily removed during maintenance.

The medias for the growth of the biofilm are packed in bags. The bags can be partially taken out of the reactor and rinsed outside. The cleaned bags can be used again. At no time the material has to be replaced for new material. The packing can be used for the whole lifetime of the treatment plant.

If the treatment plant will be taken out of order in the future and will no longer be needed the material (plastic) can be recycled. It is even possible that due to rising prices of oil a premium for the operator can be obtained for the plastic parts since the material will highly contain energy in 20 years.

Which containers are used for ClearFox® nature?

In combination with the technology of the ClearFox® nature plants results an almost unbeatable overall system, in particular by minimising the installation costs.

As the proven reservoir the aquaplast container system is used. The containers have also been successful for other treatment systems on the market (see for several years. They are made of high-quality, recyclable plastic materials and are subject to a foreign monitored (DEKRA) quality control.

The container system is especially suitable for the underground installation and has in comparison with conventional tanks the following features:

  • all test certificates for underground installation (vertical and horizontal load test acc. DIN EN 12566-3)
  • low installation depths
  • additional static stiffeners
  • lightweight and extremely compact
  • easily to use (optimised for transport and installation)

Why is the production of primary sludge lower than in other small treatment systems?

The settling of primary sludge in the primary treatment tank is neither disrupted by recycled, oxygenated water nor by refluxing excess sludge. The sludge may therefore unaffected rotten and thicken, leading to a reduction of the volume.

Which treatment classes reaches the plant?

Treatment class C

CE certificate and Official Approval?

The containers have been successfully approved on the market for several years according to DIN EN 12566-3.
The whole system has the approval numbers Z-55.41-420 and Z-55.41-583

What is unique about ClearFox® nature compared to the offer of other septic system manufacturer?

A unique feature is the combination of a fully biological wastewater purification by biofilm with aerobic sludge treatment (minimising the secondary sludge volume, no secondary clarification necessary) with a low filtration efficiency.

In addition to it ClearFox® nature also has got a number of advantages, that also offer other manufacturers partly, but not all in a single installation:

  • requires no energy
  • undisturbed primary sludge thickening / digestion
  • lightweight and compact
  • no water recycle and no sludge recirculation
  • modular construction
  • no secondary clarifier
  • low operating costs and low maintenance
  • purification in a cascade and particular adapted media for the growth of the biofilm

Are all parts of ClearFox® nature recyclable?

Yes, of course all! Compared to conventional systems, this treatment plant is 100% recyclable. There is no part of the plant, which cannot be recycled (after cleaning) in the material cycle. As materials PE, PP, ABS and stainless steel are used.

What should I do if I want a small sewage treatment?

  • Get infomation at different companies
  • Seek listing at the foreign service of PPU
  • Compare domestic wastewater treatment systems, compare investment and operating costs
  • Clarify formalities with the low water authority
  • Purchase of the plant (contract with PPU or the licence with PPU)
  • Delivery of the system (supply with trucks, containers are light and compact)
  • Installation (by civil engineering companies; dredging, levelling at ground level, installation instructions, operation manual)
  • break-in (cleaning works immediately, outflow requirements are achieved after a few months)
  • Operation (note the operation manual, don’t use any disinfectants)
  • Holidays or short-term overloads by celebrations and visits cause no problems
  • Sludge disposal (note the operation manual, sludge dsiposal due to operation and amount of sludge, measurement of sludge level in the primary treatment tank)
  • Maintenance (according to legal requirements by certified maintenance companies)

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FAQ – ClearFox® nature
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