Progressive Cavity WAS & TWAS Pumps
Controlled transfer of waste activated sludge and thickened waste activated sludge to thickening, digestion, storage and dewatering processes.
From WAS to thickened WAS
Waste activated sludge is intentionally removed from the activated-sludge process to control biomass inventory and sludge age. After thickening, TWAS contains a higher percentage of solids and generally exhibits greater apparent viscosity. That change can significantly affect pump suction, torque and power requirements.
Positive displacement remains useful as biological sludge becomes concentrated and harder to move.
Pump output can be adjusted through rotational speed and VFD control.
Progressing cavities can transport concentrated biological solids when inlet conditions are adequate.
Useful for conditioned sludge and downstream dewatering processes.
WAS and TWAS require different attention
Conventional WAS selection begins with flow, solids, pressure and suction conditions. TWAS often creates a more difficult inlet problem because higher solids can raise apparent viscosity and pipe friction while reducing the rate at which sludge fills the pump cavities.
Solids percentage does not tell the whole story
Two sludges at similar solids concentration can pump differently because of biological composition, conditioning, temperature and shear history. When viscosity or rheological data are available, they should be included in pump selection.
Speed and abrasion
Grit and abrasive particles can accelerate rotor and stator wear. Conservative operating speed, appropriate rotor surface and suitable stator elastomer should be considered for abrasive service.
Feeding digestion and dewatering
WAS and TWAS may be pumped to digesters, holding tanks, centrifuges, belt presses, screw presses or filter presses. Each downstream process creates different flow and pressure requirements, while dewatering performance can depend on coordinated polymer addition.
Protecting WAS and TWAS pumps
Progressive cavity pumps require protection appropriate to positive-displacement service. The pumped fluid also lubricates and cools the rotor/stator interface.
Recommended protection
- Discharge-pressure protection
- Dry-run protection
- Motor overload protection
- VFD operating limits
Need help selecting a WAS or TWAS pump?
Send the sludge type, solids range, viscosity if known, required flow, discharge pressure, suction arrangement, temperature and existing pump information.