Engineered For Your Success

OSE decanter
for sludge

OSE = optimum sludge thickening

The decanter centrifuge for the thickening of sewage sludge

In the process of treating waste water, fine biological sludge is constantly produced during the decomposition process at a sewage treatment plant. For a stable decomposition process in the biological treatment phase, the sludge produced in the secondary sedimentation pond, also known as excess sludge, is removed and fed into the digestion tower. Flottweg's OSE decanters thicken the sludge before it enters the digestion tower. Sewage treatment plants benefit from an even feeding of the digestion tower and can thus optimally use the volume of the digestion tower. The Flottweg OSE decanter is specially designed for sludge thickening. Thus this thickening centrifuge achieves considerably better separation qualities than other centrifuges.

More than 50 years of experience and know-how in the field of sewage sludge thickening flow into our Flottweg OSE decanters. The thickening decanter is thus convincing in terms of reliability, high economy and minimum maintenance.

For use in the thickening of sewage sludge


The sludge thickening process

Thickening sewage sludge means concentrating excess sludge that accumulates in the biological phases of the sewage treatment plant. Learn more about the process of sludge thickening and sludge treatment.


Innovative sewage sludge thickening with starch polymer

Thickening sludge with starch polymer requires the use of potato or pea starch polymers instead of synthetic polymer flocking agents. Here you can find out how to keep throughput rates high.

Operating principles of a Flottweg OSE decanter

The excess sludge from the secondary clarifier is pumped into the OSE decanter. This separates the solid from the liquid by means of centrifugal acceleration. The excess sludge is thickened from 0.5 - 1 percent (5-10 grams per liter) dry matter (DM) to 6 - 8 percent DM.

The dry matter content in the thickened sewage sludge depends on the pumpability of the thick sludge and the thickening equipment used.

The illustration shows how a Flottweg C-series decanter centrifuge works. Our OSE decanters belong to this series. Cross section of a Flottweg OSE decanter of the C-series

Product features


Flottweg OSE decanters keep the discharge of dry material constant, thereby feeding the digestion tower steadily and maximizing gas yield. The continuous and automatic control to a predetermined dry matter content, e.g. 6 percent, leads to efficient and stable digestion. The Simp Drive® concept generates a differential speed between the centrifuge bowl and scroll. This is decisive for the time the sludge remains in the bowl. With Flottweg OSE decanters, the differential speed is automatically adjusted depending on the current load in the machine. This means that the thick sludge concentration remains constant even with changing feed conditions.

The Flottweg OSE decanter is specially designed for sludge thickening. This enables them to achieve better performance than comparable units. A special scroll design with deep pond and steep cone increases the sedimentation volume in the decanter bowl. This enables a higher output density (10 - 20 percent) and makes the system more efficient.

  • Highest gas yield through constant feeding of the digestion tower
  • Best possible thickening even with changing feed conditions
  • Larger sedimentation volume (due to deep pond and steep cone) enables highest power density (10 - 20 percent) with minimum space requirement

Cost saving

Thickening centrifuges are operated at a very low primary speed, which keeps the electrical power requirement low. In addition, the Flottweg Recuvane® system reduces energy consumption by a further 20 %. The OSE decanter has a very low flocculant requirement of only 1-2 g/kg dry matter. Even polymer-free operation is possible. Lower quantities of flocculant and less energy are required, which leads to significant cost savings compared to other thickening equipment such as belt thickeners. Thanks to the compact design of the OSE decanter, there is a considerable reduction in floor space requirements. This makes replacement investments possible without any additional construction work.

  • Lowest operating costs due to reduction of the required flocculants and lower energy consumption
  • Additional 20 % energy saving when using the Flottweg Recuvane® system
  • Low space requirement allows replacement investment without construction work


The OSE decanter was specially designed for optimized maintenance. The maintenance-friendly and easily accessible design ensures that downtime can be kept to a minimum when maintenance work is required. Wear protection measures, the use of high-quality stainless steels and replaceable wear parts minimize maintenance costs considerably - quality made in Germany pays.

  • Maintenance-friendly, easily accessible design promotes minimal downtime
  • Maximum service life through the use of optimized wear protection measures and high-grade stainless steels (corrosion and acid resistant)


In addition to minimizing maintenance costs, the operating expense of an OSE decanter is also minimal. The user-friendly control system, the Flottweg Touch Control, allows easy operation of the thickening centrifuge. The new InGo user interface facilitates simple control. Thanks to InGo, all important control parameters are visible at a glance. The thickening decanter can optionally also be used in automatic 24-hour operation. For this purpose, the centrifuge is switched on and off in a timed cycle. The operating personnel who are still required are not exposed to any health hazards during operation, as the centrifuge is a closed system. This prevents aerosol contamination or the escape of dirt and odors.

  • Automatic 24-hour operation, incl. time-controlled on/off switching
  • No health hazards for operating personnel (no aerosol or odor nuisance)
  • Simple operation and user-friendly control with Flottweg Touch Control and InGo.

Germany's oldest city relies on a Flottweg OSE decanter

The wastewater treatment plant Trier uses a Flottweg OSE decanter for the treatment of sewage sludge. The decanter centrifuge is used to thicken the excess sludge from the sewage treatment plant.

Before the purchase, different plants were compared with each other. The decision was made in favor of a centrifuge from Flottweg. You can see why, and with which results, in this video.


Would you like to find out more about our OSE decanter for sludge thickening?

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