Product Information
A decanter is the equipment used in the SBR (sequencing batch reactor) process to draw off the supernatant. Once the reaction tank has finished settling, the clear water on top needs to be removed—but without dragging sludge up from the bottom. A rotary decanter rotates its main pipe and branch arms to skim the clear water off smoothly, with the weir staying right at the surface as the water level drops. An SBR decanter usually has a float or mechanical guide that adjusts the angle as the level falls, and it stops automatically at the end of the draw. The whole process leaves the settled sludge layer undisturbed and keeps suspended solids in the effluent low.
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Working Principle
In the SBR cycle, the rotary decanter starts working once settling is done. A motor or hydraulic actuator rotates the main pipe, and the weir on the branch arms swings down into the water surface. Clear water flows over the weir into the branch arms, collects in the main pipe, and discharges out of the tank. As the level drops, the rotary mechanism keeps the weir close to the surface so sludge from the bottom doesn't get pulled out. When it reaches the set low level, the unit shuts down and resets. Float-type decanters use buoyancy to hold the weir position automatically, while actuator-type units use mechanical limits to control the rotation angle.
Application Fields
1.Municipal wastewater: the draw-off phase in SBR and its variants (CASS, CAST).
2.Industrial wastewater: solid-liquid separation and draw-off in batch biological treatment systems.
3.Water reuse: SBR effluent goes to filtration or disinfection, with the decanter keeping suspended solids within spec.
4.Small integrated units: clear water discharge from buried or containerized SBR systems.
FAQ
Q1: How deep can a rotary decanter typically draw down?
A: Usually 1.0–2.5 meters, depending on tank design and process requirements. The deeper the draw, the more the main pipe has to rotate, which means a longer stroke and better sealing. If the water level changes by more than 3 meters, you'd generally look at a lifting-type or another decanter design.
Q2: Why do SBR decanters use a rotary design?
A: The rotary design lets the weir drop smoothly along an arc, giving even outflow and minimal disturbance to the settled sludge. Draining from a bottom opening like a conventional outlet would send water downward and easily carry sludge out. A rotary decanter skims right at the surface, so effluent quality stays good.
Q3: Can a decanter pull out floating scum during operation?
A: The weir sits right at the surface, so if there's scum on the tank, it can get drawn out. SBR tanks usually have a scum baffle or skimmer in the front section, or some scum is removed before draw-off. The weir design itself matters too—some decanters come with scum guards to keep surface float from getting in.