Compact WWTP

Compact WWTP DELPHIN® cube

DELPHIN® cube is the new system solution for decentraliced wastewater treatment from DELPHIN Water Systems. The submerged and aerated fixed bed is a very stable and low-maintenance process for biological sewage treatment. This results in little effort for the operator and high operation reliability, even with severe load variations, e.g. at seasonal hotels or campsites.

System tank DELPHIN Q

  • fully biological fixed-bed process
  • available for 60 to 1200 population equivalents (PE)
  • treatment classes C, N, D, +P, +H
  • earth placement, above ground installation or installation inside ISO containers
  • flexibility through modularity and multiple line concept
  • extensive service

Reliability and flexibility through independent, parallel treatment lines

The heart of every DELPHIN® cube plant is the fixed-bed. Depending on the plant dimensioning, it can be realized in one or two consecutive stages. Together with the secondary clarifier, it forms a standard module of a biological treatment line. To increase the treatment capacity, several treatment lines can be installed in parallel. Each treatment line can be operated independently and parts of the plant can temporarily be shut down while the others remain active.

Safe energy and money during off-season

Especially in seasonally operated businesses, like hotels, you can save a considerable amount of money by putting parts of the wastewater treatment plant in stand-by mode during off-season. Thanks to the fixed-bed technology, the biofilm in unused treatment lines can be kept alive with low energy effort and quickly be reactivated in case it is needed.

Repairs during runtime

During repairs of one treatment line, the others can temporarily compensate for the missing treatment. Therefore, during downtime of one line, all water still receives at least a basic treatment.

Strong tank

More than 12 years of engineering know-how – accumulated into one tank

Since 2005 DELPHIN Water Systems develops and distributes decentralized wastewater treatment systems. The further development of our modular treatment system DELPHIN® combi gave our engineers the opportunity to use the experience in tank design for the creation of a unique cubic polyethylene tank. The result: the new system tank DELPHIN® Q

Extremely robust and space-saving

  • No welding seams or seals
  • Ideal absorption and distribution of all loads

The unique design of DELPHIN® Q is based on the optimal usage of volume in excavation pits and containers, while guaranteeing the best vertical and horizontal load flux through the walls in different on-site conditions. During the production of the tank so called „kiss-offs“ form along the joining points of the three dimensional wall structure. Together, they act as a frame that supports the mechanical loads from soil on the outside and water on the inside and give the tank stability in different load cases. Due to the rotomoulding process, the tank is monolithic, i.e. made of one piece. That makes it perfectly watertight and durable, as there are no welding seams, rubber seals or screwed joints involved, which are typical weak spots of other tank forms.

  • Underground or aboveground installation
  • Installation in groundwater
  • Installation in ISO sea freight container

Practical details

  • Integrated guidance for transport by forklift without demand for pallets
  • The patented aeration system with membrane tubes allows the simple replacement without removal of the fixed-bed

Clever modules


The pre-treatment essentially consists of empty tanks, which are equipped with submerged overflow pipes. In these tanks, solids can settle and floating material swims up. The resulting primary sludge can be stored for 3 to 12 months. If there already is a mechanical treatment on site that merely needs to be supplemented with biological treatment, it is possible to combine standard modules consisting of fixed-bed reactors and secondary clarifier with the existing mechanical treatment stage(s) => DELPHIN® combi-cube

Fixed-bed reactor

The submerged and aerated fixed-bed serves the biological treatment of dissolved pollutants. The necessary air for the aeration is brought in from the outside by a side channel blower. The air is distributed underneath the fixed-bed by a membrane aerator. The membranes can easily be changed if necessary without having to remove the fixed-bed, first.

Secondary clarifier and sludge recirculation

In the secondary clarifier, the secondary sludge that is produced in the fixed-bed separates from the treated wastewater. This sludge consists of flocs that have been torn off the biofilm with very good settling properties. Therefore, the secondary clarifier can be dimensioned comparatively small, while still guaran- teeing very low suspended solid concentrations in the effluent.

Compact wastewater treatment plant DELPHIN cube for a population equivalent of 220 PE
Example: DELHPIN® cube 220/C/6

Tertiary treatment: Disinfection & phosphate elimination

Tertiary treatment with DELHIN® clean-kit makes the treated wastewater fit for re-use through sand filtration and disinfection by means of UV radiation. After this treatment, it can be used for irrigation of green spaces. Phosphate elimination through chemical precipitation or adsorption can also be added.

Reliable process

The fixed-bed technology

As biological treatment process, the fixed-bed technology is based on different microorganisms, which naturally occur in domestic wastewater. Contrary to sludge-based processes, these organisms don’t need to be kept in suspension as activated sludge in the reactor, but have a fixed surface to grow on, the so called fixed-bed. Due to their special structure, the fixed-bed elements have a high specific surface for increased contact between the biofilm and the wastewater. The air for the aerobic processes is brought in from the outside by a side channel compressor. Underneath the fixed-bed the air is dispersed evenly in small bubbles by membrane diffusors. The specific arrangement of the aerators causes a vertically circulation flow, which guarantees a homogeneous mixing in the reactor.

Stable process at variable load

Small treatment plants and treatment systems for seasonally operated facilities, such as hotels must deal with a high variability of organic load. That is why decentralized treatment plants must be especially capable of adapting to changing conditions. Fixed-bed technology has this ability like no other. The cleaning microorganisms have a fixed surface on the fixed-bed to grow, on which the thickness of the biofilm adapts to the actual load. It can also endure longer phases of underload, and recovers quickly from starvation.

We provide a performance guarantee for under load phases on all our WWTP!

Simple technology with very little control effort

Wastewater treatment plants with fixed-bed technology can be operated purely by gravity flow. Therefore, the use of error prone and maintenance intensive mechanical components, such as pumps, can be minimized. This leads to a minimized maintenance effort and reduced follow-up costs.

Less solids in the effluent

Sludge based processes, like SBR, must maintain fine sludge flocs in suspension in the reactor during the biological treatment. The removal of this secondary sludge after the biological treatment requires extensive secondary clarification with long retention times. Often, an elevated suspended solids concentration during peak flow must be accepted. The biofilm in fixed-bed plants detaches itself in bigger flocs with high specific weight and, therefore, with good settling properties. This results in a good separation efficiency and very low solids concentration in the effluent.


  • Habitation: remote residential complexes, smaller settlements, apartment complexes
  • Tourism: hotels, sports facilities, campsites
  • Industry: commercial parks, shopping centers, offices, schools and other facilities whose wastewater is comparable to domestic wastewater
  • Surface water: e.g. organically contaminated precipitation or silage seepage water in biogas plants and livestock

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Brochures for download

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The experts for fixed-bed technology

DELPHIN Water Systems GmbH & Co. KG in Buxtehude/Germany is one of the leading manufacturers of fully biological wastewater treatment plants with fixed-bed technology. Our business activities include the dimensioning and delivery of pre-assembled small scale WWTP, compact WWTP and WWTP in containers as well as services related to decentralized wastewater treatment, such as installation, maintenance, optimization and operation management.


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