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Rotary Disc Dryer

HUBER’s RotaDry is a compact and efficient method to dry municipal sludge to 40 – 45%DS. Sludge disposal costs are slashed by over 50% due to the volume reduction.

Rotary Disc Dryer

The HUBER RotaDry Disc Dryer has been designed to dry municipal sludge to up to 40-45% dry solids, which results in a significant cost reduction for offsite transport and allows the opportunity for expanded biosolids reuse or use as a fuel source.

Exhaust heat from biogas processes, or hot water generated in anaerobic digester heat exchanger loops are commonly used as the heat source, providing a sustainable balance that reduces CO2 impact and operating costs.

The dryer is very compact with a small footprint relative to full thermal drying. It is an ideal process step upstream of sludge incineration plants.

How it works

The HUBER RotaDry® Disc Dryer is designed for partial drying of dewatered sewage sludge, allowing for a reduction in disposal costs or as a pre-cursor to advanced sludge treatment processes such as incineration.

From a sludge bunker, the sludge is transferred to the dryer by a multi stage pump through an opening in the main dryer body. The internal mechanism of the dryer consists of a series of hollow discs that are welded to a rotor.

Saturated steam disperses through the discs which elevates the internal temperature. The steam comes from a turbine which generates electricity from the heat produced during combustion. Before entering the dryer, the steam must be conditioned so that it flows into the interior of the rotor as saturated steam. At the surface of the discs the vapour reaches its condensation temperature.

The rotor is driven by a 3 phase geared motor, the speed of which can be controlled by a frequency converter. Dewatered sludge is normally supplied with a dry solids content of 15 – 30% w/w.
As the heat in the dryer rises the rate of water evaporation of increases the dryness of the sludge. The (partially) dried sewage sludge leaves the dryer with 40 – 45% DR via the discharge screw.

A vapour dome draws off the water vapour produced where the heat within the vapour is recovered in a condenser. The heat recovered can be fed back into the heating network or used to pre-heat sludge prior to dewatering.

Treatment of the condensate forms part of the overall package. As a result of the high contact temperature on the discs, the condensate contains a high load of particulate/dissolved COD and increased ammonium content.

A condensate treatment system comprising of filtration, adsorption and stripping treats this wastewater stream prior to return to the main sewage flow at the inlet works.

The HUBER RotaDry® is available in different sizes so that water evaporation of two to six tons per hour and dryer can be achieved. By using different disc diameters and numbers of discs, the dryer surface can be optimally adapted to the amount of generated sludge and the disc dryer can be operated in the ideal capacity range.


  • Compact design with small footprint
  • Proven and durable technology
  • High specific water evaporation capacity
  • Heating of the rotor discs and optionally of the jacket allows for high volume-specific water evaporation.
  • Consistent drying – continuous discharge of dried material
  • Consistent contact of sludge and heat via the mixing pattern generated by the internal rotor
  • Heat recovery through use of condensation heat
  • The water evaporated from the sewage sludge can be precipitated again in the vapour condenser, whereby part of the energy used for thermal drying can be recovered.
  • Reliable condensate removal
  • Optimised humidity control for the partially dried sludge by integrated DR measurements at the dryer inlet and outlet
  • The control of the disc dryer is dependent on the detected DR content at the inlet and outlet. This provides the possibility to react to fluctuating DR contents of the dewatered sludge.


RotaDry 18/54 20/50 20/64 22/64
Max Water Evapotration (kg/h) 3300 4000 5000 5700
Disc Diameter 1.8 2.0 2.0 2.2
Disc 54 50 64 64
Dewatered Sludge Throughput (kg/h) 9000 10500 13200 15400

Note – capacities are guide values; consult Hydroflux Epco for specific details


HUBER RotaDry Contact dryer for sewage sludge

HUBER RotaDry Contact dryer for sewage sludge Case Study

Hydroflux Epco NZ is a New Zealand business dedicated to providing world leading wastewater technology and processes to Water Authorities and Councils