Wastewater treatment operators working with Sequencing Batch Reactor (SBR) processes or high-volume filter-backwash streams face a common challenge: how do you reliably remove clarified water from the top of a settling tank without disturbing the settled solids below? The answer, employed across the industry for decades, is the floating decanter — a deceptively simple piece of equipment that plays a critical role in achieving consistent, high-quality effluent.
What Is a Floating Decanter?
A floating decanter is a device designed to discharge the upper layer of treated wastewater during the settling stage of a batch treatment cycle. Rather than being fixed at one height, the unit floats on the surface of the water, rising and falling with the liquid level in the tank. A flexible hose and a set of valves connect the floating intake to a clear water tank, or in some configurations, directly to the public sewer system.
This “solids-excluded decanting” approach ensures that only the clarified supernatant — the layer of treated water sitting above the settled sludge — is drawn off, while the biomass and solids remain undisturbed at the bottom of the tank.
How the Technology Works
The floating decanter combines advanced tube-settler enhanced clarification with a variable operating liquid level. As the surge or reaction basin fills during the treatment cycle, the decanter floats upward with the rising water. Once the settling phase is complete, the decanter draws off the clean upper layer, which is then replaced the following cycle with freshly supplied wastewater ready for the next round of treatment.
This fill-and-draw operating principle is the backbone of the classic Sequencing Batch Reactor process design, as well as systems handling high-flow, short-duration events like filter-backwash wastewater.
Because the unit tracks the liquid surface automatically, it always draws from the correct depth — never too close to the settled solids, and never skimming only the very top where scum can accumulate (an issue addressed with optional scum-proof ports).
Key Features
Floating decanters are built to perform reliably across a wide range of site conditions and process requirements:
- Wide range of design configurations to suit different process needs
- All-weather performance
- Manual control or fully programmable automatic control
- Gravity or pumped discharge options
- Optional scum-proof ports
- Low center of gravity for stability
- Heavy-duty float available in a range of materials
- Wide range of vertical travel to accommodate varying tank depths
- Easy to maintain
Technical Specifications
| Parameter | Detail |
|---|---|
| Flow rates available | 5 to 250 m³/hour |
| Standard material | 304 stainless steel |
| Materials | Selected to suit application requirements |
| Configurations | Circular, rectangular, submerged multiple-orifice, floating arm, flexible arm, enclosed all-weather |
| Temperature range | No practical limit |
| Pressure range | No practical limit |
| pH range | No limit |
| Corrosion resistance | Wide range of materials available to suit conditions |
| Ancillaries | Guide rails, level monitors, manual/automatic height control, alarm indication, service winch, surge management |
Materials and Construction
The standard decanter is fabricated from 304 stainless steel rather than alternatives such as glass-fibre reinforced plastic (GRP). Stainless steel was selected as the standard because of its high resistance to degradation from ultraviolet exposure and its ability to withstand temperature fluctuations — both important considerations for equipment that operates outdoors, often exposed to the elements year-round.
Decanters are passivated after welding specifically to preserve the stainless steel’s corrosion resistance, and all seals are made from synthetic materials for prolonged service life.
Units are shipped factory-assembled to simplify on-site installation, and the rugged construction has been field-proven in harsh operating conditions. For non-standard applications, alternative materials can be specified to suit specific corrosion or environmental demands.
Design Philosophy
The guiding principle behind this equipment is to keep the design as simple as possible while maximising functionality and reliability. This matters enormously in real-world operations, where treatment plant technicians need equipment that is straightforward to understand, operate, and maintain — minimising downtime and simplifying troubleshooting when issues arise.
Typical Applications
Floating decanters are most commonly found in:
- Sequencing Batch Reactor (SBR) processes — a widely used activated sludge treatment configuration where fill, react, settle, and decant phases occur sequentially in the same tank
- Filter-backwash wastewater treatment — handling high-flow, relatively short-duration discharges that need efficient clarification before reuse or discharge
Beyond the Decanter: Full Process Solutions
Floating decanters are often just one component within a broader wastewater treatment strategy. Complementary equipment and process packages include:
- JetOX venturi aerators
- Complete SBR packages
- Ammonia stripping systems
- Reedbed treatment systems
- Methane stripping systems
For projects at the planning stage, early involvement in design and dimensioning can help ensure that ancillary equipment — valves, instrumentation, pumps — is correctly specified from the outset. Full installation management, from tank construction through to pipework, control wiring, and commissioning, can also be provided, with a process guarantee available where full design responsibility is undertaken.
Key Takeaways
- Floating decanters remove clarified supernatant from settling tanks without disturbing settled solids, floating with the liquid level throughout the treatment cycle.
- They are core equipment in SBR processes and filter-backwash treatment applications, handling flow rates from 5 to 250 m³/hour.
- Standard construction uses passivated 304 stainless steel for durability and corrosion resistance, with alternative materials available for specialised conditions.
- Configurations range from circular and rectangular designs to floating arm and enclosed all-weather units, with manual or fully automatic control options.
- The equipment is designed for simplicity, reliability, and easy long-term maintenance.
Get in Touch
If you’re designing or upgrading a batch wastewater treatment system and want to explore whether a floating decanter is the right fit for your process, our team can help with specification, design, and full turnkey installation. Contact us today to discuss your project requirements and find the right decanting solution for your site.