Secondary Clarification

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Continuous biological wastewater processes typically use secondary clarifiers as the phase separation step to separate biomass from the water phase. The overflow is the secondary treated effluent, which is typically disinfected and discharged to the environment, or reused.

Settled biomass is wasted to a biosolids facility (Waste Activated Sludge, or WAS) to control the biomass concentration within the biological wastewater process, and a return stream (Return Activated Sludge, or RAS) is pumped back to the head of the process.

Hydroflux Epco have extensive expertise and references on secondary clarifiers as follows:

  • Over 300 secondary clarifier systems manufactured since 1962
  • Robust construction with proven sludge removal systems

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Key Advantages
More Information
Principle of Operation
Case Studies
  • Proven bridge construction
  • Proven effective sludge removal systems
  • Elimination of dead zones
  • Elimination of denitrification
A number of designs and configurations are available, these include:
    • Centre Drive
    • Peripheral Drive
    • Full bridge
    • Half bridge

A clarifier is essentially a gravity process which separates suspended solids from the liquid. The clarifier mechanism collects both the sludge (heavier material), and scum (lighter material) by physical means. There is one flow inlet to the tank and multiple outlets.

In operation, the influent enters the clarifier tank through the ports in the centre column. High radial inflow currents are suppressed by the EdiGate® energy dissipation inlet (optional) which redirects self cancelling tangential flows to the outer FlocWell™ feedwell, which in turn, directs the flow downward toward the bottom of the tank.

The major concentration of heavier material settles below the EdiGate™ and FlocWell™ flocculation skirt, with lighter material settling in the tank extremities.

The sludge is collected by the scraper blades due to their rotation, and is moved across the floor to the sludge pocket in the centre of the tank, by the floor slope and the spiral blade pattern. The sludge is then removed from the centre pocket via pumps or gravity.

Scum on the water surface is removed from the tank via the radial scum scraper, the hinged skimming mechanism and scum boxes. The scum boxes have a bottom dump valve which is actuated every revolution by a striker mounted onto the underside of the bridge.

The inside of the peripheral scum baffle is wiped continuously every revolution, by a rubber wiper attached to the hinged skimmer.

Clarified effluent leaves the tank via the peripheral vee notched weir plates and launder channel.