Suction Pipe Versus Spiral Blade Clarifier
Suction Pipe vs. Spiral Blade Clarifier Designs – Pros & Cons
Please note that this comparison focuses on the sludge collection features of these two styles of mechanism rather than the clarification process, which is identical.
Suction Pipe Design (Type C3S)
Removal of sludge is through differential head pressure between the liquid level of the clarifier and the liquid level in the sludge collection box. Sludge flows through vertical and horizontal lengths of PVC pipe into valved openings in a central sludge box, where it reaches a free surface condition, and then out of the clarifier through a return activated sludge (RAS) pipe that is inside and concentric with the center column. There are two flow control points – the sludge valves and the RAS pump.
PRO: The sludge collection box is at liquid level, which allows operators to view and sample sludge from the walkway or platform. Samples can easily be removed from individual pipes, which represent the section of the floor covered by that pipe.
PRO: Sludge pickup is varied among the pipes for selective operation.
CON: Balanced control of sludge pickup can be difficult to obtain with the multiple valves of the sludge pipes.
CON: Pipes can plug at low flow velocities.
CON: Pipes are typically sized for a total withdrawal rate and not for the proportion of the floor covered by each pipe.
CON: Fixed hydraulic design on pipe return system.
CON: For new machines, special tank floor construction is required for the RAS pipe, which is installed inside the influent pipe.
Spiral Blade Design (Type C4)
Removal of sludge is through sludge movement along the sloped tank floor by the spiral blades rotating at an optimum speed as determined by the operator. The continuous, tapered blade moves sludge quickly to the center of the tank for withdrawal through the OVIVO® rotating sludge collection drum, which collects sludge continuously from the leading edge of the spiral blades. Sludge then flows within the drum to the withdrawal point on the tank floor and exits the clarifier.
PRO: Tapered blades move deeper and deeper masses of sludge to the tank center, along the sloped floor, helping consolidate and thicken the sludge prior to withdrawal.
PRO: Continuous blades oriented at a 30º angle of attack allows rapid return of the sludge to the tank center and withdrawal point.
PRO: Variable speed capability allows operators to fine tune sludge collection, minimize sludge blanket agitation and reduce sludge blanket height when needed.
PRO: Spiral blades are low maintenance and low operator attention. No problems with plugged withdrawal pipes or sludge valves.
PRO: Rotating sludge collection drum collects the thickest sludge that the clarifier can produce.
PRO: No hydraulic limitations other than RAS pipe size and RAS pumping capacity.
CON: Sludge return time is not as rapid as suction designs.