Wastewater Treatment Glossary: What Is a Decanter?

The decanter is a key piece of equipment in sequencing batch reactor (SBR) processes and their variants, such as CASS, CAST, ICEAS and DAT-IAT, which are used to treat municipal sewage and industrial wastewater. It is widely applied in the treatment of effluents from the papermaking, alcohol, dye, pesticide, leather, viscose fiber, monosodium glutamate and sugar industries, where it withdraws the clarified supernatant after sedimentation without disturbing the settled sludge or the floating scum layer.

Structure and Working Principle

A decanter typically consists of a decanting weir, branch pipes, a main pipe, a 360° rotating slewing support, sliding supports, a drive unit and an automatic control system. During operation, the drive unit moves the decanting weir downward in a variable-speed circular motion around the axis of the slewing support at the base of the decanter. The clarified supernatant in the SBR reactor flows over the weir into the branch pipes and is then discharged through the main pipe. Once decanting is complete, the weir rises at a uniform speed around the same axis back to its standby position, where it waits until the filling, biochemical reaction and settling stages have finished before the next decanting cycle begins.

Key Features

1. The decanting depth can be designed to meet specific process requirements.

2. With a PLC-based intelligent drive, the decanter moves the weir quickly from its parked position to below the water surface as soon as a discharge command is received, drains the settled supernatant, and repeats the cycle. When the lowest water level is reached, a level switch installed at that position issues a return command, and the decanter rapidly rises back to its initial parked position, completing one working cycle.

3. Within the designed loading range of the weir, the liquid surface beneath the weir is not disturbed. The weir is fitted with a float and a scum baffle to ensure effluent quality.

4. A special design keeps the gravity of the decanter and the buoyancy acting on it essentially in balance, so the drive power consumption is very low.

5. The connection between the decanter and the main drainage pipe is a rigid stainless-steel joint, avoiding the high failure rate, short service life and heavy maintenance burden associated with flexible connections.

6. The entire decanter is mounted on a robust frame capable of withstanding the various stresses encountered during operation.

Power-Free Decanter (WFT Type)

The main body of this type operates without external power: apart from an electric valve installed at the discharge outlet, no powered components are used anywhere in the equipment. The WFT power-free decanter is a highly automated water treatment device whose use with the SBR process for municipal sewage treatment has been widely promoted in China; the decanter, as the core equipment of the process, is particularly important.

1. The main body adopts a U-type rotating support, and all components are made of stainless steel, giving a compact assembly and smooth operation.

2. The float uses a floating design that keeps the depth of the decanting layer constant despite continuous changes in the tank water level, achieving the best decanting effect.

3. During operation the decanting speed is uniform, the water surface is calm and free of waves, the main drive produces no noise, and after decanting the unit floats up continuously as the water level rises.

4. The underwater rotating parts use a mechanical rotation device, ensuring that the rotating assembly can operate for a long time without aging or breakage.

5. The main body contains no rubber components, giving it a long service life.

6. During normal operation, the decanting range can be freely adjusted between 0 and the maximum decanting depth through the electric valve.