Process Wastewater Technologies LLC

- Volute Sludge Thickener



The PWTech Volute Thickener is a fully-automated, virtually maintenance-free unit using the 'dewatering drum' design used for the Volute Dewatering Press. The Volute Thickener is perfect for automated sludge wasting from biological processes and thickening prior to storage, digestion, further dewatering, or transport, giving a solids output from 3% to 6%. The unit can be completely automated, uses very little power, and can be run over 30,000 hours between overhauls.

In the fall of 2008, Process Wastewater Technologies began piloting and selling the Volute* Thickener in the United States. This technology has been used extensively in Japan and has many of the benefits that is fast making the Volute Dewatering Press the go-to technology for many dewatering applications.

The Volute Thickener design is based on the patented dewatering drum design used for the PWTech Volute Dewatering Press sludge dewatering unit. The Volute Thickener is a very simple piece of equipment that is virtually maintenance-free and fully automated. It is designed to take dilute sludges and thicken them allowing for more cost effective storage, dewatering, or transport.

Application of this technology includes automated sludge wasting from biological processes and thickening prior to storage, digestion, further dewatering, or transport.

In a wastewater (sewage) treatment plant, waste sludge is typically around 0.4% to 0.8% solids. Typically the Volute Thickener can be adjusted to give a solids output in the range of 3% to 12%.

  • Fully automated: the unit can operate itself from start-up to shutdown, allowing 24-hour unattended operation.
  • Integrated system: the Volute Thickener is sold as a complete package for the entire sludge thickening process, including polymer system, feed pump (if required), flocculation tank, and controls.
  • High solids recovery: typically over 99% of the solids are retained in the thickener so the filtrate is very clean and may not need to be returned through the entire treatment process.
  • Very low power consumption: all motors are less than one horsepower, even on our largest units.
  • Low maintenance requirements: units are designed to run in excess of 30,000 hours between overhauls. That’s over 10 years at 8 hours per day, 7 days a week!
  • Zero wash water requirements under regular operation.
  • High-quality construction: stainless steel and engineering plastics, high quality “sealed-for-life” drive motors, and robust, durable design result in long life and low maintenance.

  • Dilute sludge is dosed with polymer as it enters a flocculation tank.
  • The sludge is gently mixed in the tank, separating into discrete agglomerations of solids (flocs) and free water, and then overflows into the thickening drums.
  • Free water is discharged through the gaps in the thickening drum while solids are conveyed along the length of the drum and discharged at the opposite end.


The dewatering drum utilizes a series of fixed rings that are held together on tie rods and separated by spacers to form a cylinder around an Archimedean screw (see illustration). Between each fixed ring is a moving ring which is slightly narrower than the spacers and creates fine gaps between the fixed and moving rings. The moving rings also have a smaller inside diameter than the outside diameter of the screw, so as the screw rotates, it moves these rings.

The constant movement of the rings prevents the plugging of solids in fine gaps. Since the gaps are always clean, there is a continual discharge of fluid through them, allowing for very high solids capture in a very efficient operation.


While the basic design and operation of both the Thickening and Dewatering Drums are the same, the drum of the Volute Thickener is made entirely with plastic rings with a constant gap between the moving and fixed rings. The screw is a constant pitch, and there is no end plate. The drum’s motor is less highly geared to allow for greater drum speeds. In addition, the piping connections are larger and the flocculation tank is larger to accommodate higher flows.

Design Criteria

Flows of up to 400 GPM can be dewatered with a single unit. PWTech offers the Volute Thickener as a complete package, including polymer system, feed pump (if required), flocculation tank, and controls. Several models are available.

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