Low-speed submersible and hyperboloid mixers keep solids suspended and basins homogeneous — with or without coupled aeration. This page covers propeller mixer selection, hyperboloid floor-sweep design, retrievable mounting options, anoxic zone positioning, and the engineering parameters that govern thrust, power density and bearing life.
Key performance boundaries for submersible and hyperboloid mixer selection.
Low-speed, high-thrust propulsion that sweeps the tank floor without breaking the surface.
Submersible mixers generate a directed jet of high-velocity water from a propeller or impeller enclosed in a streamlined housing. The jet entrains surrounding fluid, multiplying the primary flow many times over and creating a circulating current that sweeps the basin floor, lifts settled solids back into suspension, and maintains a homogeneous mixture. Hyperboloid mixers work on a different principle: a specially-shaped impeller draws fluid upward from the floor and accelerates it radially outward in a broad, gentle plume that covers the entire tank base. Both technologies operate at low rotational speed to avoid shear damage to floc, minimise energy consumption, and prevent surface disturbance that would entrain atmospheric oxygen.
A close-coupled electric motor drives a propeller through a sealed gear or direct drive. The propeller is shrouded in a guide ring that straightens the swirl into an axial jet. Thrust is the primary specification — measured in newtons — and determines how far the mixer can influence the tank. Typical velocities at the propeller tip are 3–5 m/s, decaying to 0.15–0.3 m/s at the far wall, which is sufficient to keep MLSS in suspension without resuspending settled sludge from the secondary clarifier.
The hyperboloid impeller has a conical, open-body geometry with ribs that accelerate fluid from the floor upward and outward. Unlike propeller mixers, there is no narrow jet — the flow is distributed broadly across the entire floor area. This makes hyperboloid units ideal for tanks with irregular geometry, fragile floc, or high rag/fibre content that would bind a conventional propeller. The open design is inherently ragging-resistant and can operate in basins where other mixers would foul within days.
Four proven configurations for municipal and industrial basin mixing.
Wall-mounted or post-mounted units with angled discharge for directed floor sweep. The default choice for anoxic zones, activated sludge channels and equalisation basins.
Floor-mounted with an open-body impeller that generates gentle, full-floor circulation. Ideal for ragging-prone wastewater and delicate biological floc.
Guide-rail mounted on a sliding carriage or gantry system that allows the mixer to be lifted to the surface for inspection, de-ragging or seal replacement without draining the basin.
High-thrust impellers designed for very large basins, anaerobic digesters and sludge storage tanks where propeller mixers would be too small to influence the full volume.
Sizing boundaries and material specifications for submersible and hyperboloid mixer systems.
| Parameter | Range / Specification |
|---|---|
| Tank volume | 50–5000 m³ |
| Power density | 5–20 W/m³ |
| Thrust | 200–3000 N |
| Tip speed | <4.5 m/s |
| Mounting angle | 0–60° |
| Mixer spacing | 5–25 m |
| Materials | 304L/316L/duplex |
| Bearing life | L10 >100,000 h |
Selecting and positioning mixers for denitrification and anoxic zones where oxygen ingress must be avoided.
Anoxic denitrification requires thorough mixing to keep biomass in suspension while maintaining dissolved oxygen below the threshold where denitrification is inhibited. The challenge is that many mixing technologies entrain atmospheric oxygen at the surface, especially when mounted too shallow or operated at excessive speed.
Reynolds & Bauhm selects submersible mixers specifically rated for anoxic duty: low rotational speed, deep submergence, and directed discharge that circulates the basin without breaking the surface. Mixer positioning follows three rules:
Power density in anoxic zones is typically 5–12 W/m³ — lower than aerated zones because the goal is suspension, not oxygen transfer. Higher power densities increase the risk of surface disturbance and vortex formation. Hyperboloid mixers are often preferred for wide, shallow anoxic tanks because their broad, gentle plume does not concentrate kinetic energy at the surface.
Properly selected and positioned low-speed mixers keep MLSS fully suspended with a velocity of 0.15–0.25 m/s at the floor while maintaining dissolved oxygen below 0.3 mg/L — the threshold where denitrification proceeds without inhibition. Reynolds & Bauhm verifies this by portable DO profiling before and after mixer commissioning.
Where submersible and hyperboloid mixers deliver the most value.
Keep MLSS in suspension in aeration lanes, oxidation ditches and plug-flow reactors. Coupled with diffused aeration or operated alone in selector zones.
Provide the gentle circulation denitrifying bacteria need without adding oxygen. Critical for nutrient-removal plants targeting <10 mg/L total nitrogen.
High-thrust flow-generating impellers maintain homogeneity in anaerobic digesters, preventing stratification and scum formation while sustaining even temperature distribution.
Blend diurnal flow and load variations to deliver a steady, homogeneous feed to downstream biological treatment. Prevents septicity and odour generation.
Related aeration and mixing technologies from Reynolds & Bauhm.
Membrane disc and tube diffusers for high-efficiency oxygen transfer in deep basins.
Mechanical surface aerators for lagoons, ponds and oxidation ditch retrofits.
Pumped jet and venturi systems for deep tanks and high-intensity mixing duty.
KLa, OTR, SOTE and the correction factors that govern aeration design.
Side-by-side comparison of diffused, surface, jet and mixer-aeration technologies.
Common issues with submersible mixers, hyperboloid units and shaft-alignment checks.
Send us your basin geometry, volume, solids concentration and duty — anoxic, digester or equalisation. We will return mixer type, number, thrust rating, mounting arrangement and a predicted velocity profile.
Our expertise spans multiple industries with sector-specific water treatment solutions.