RapiSand™ Ballasted Flocculation

RapiSand Ballasted Flocculation

RapiSand™ Ballasted Flocculation Overview:

The WesTech RapiSand™ ballasted flocculation system is a high-rate clarification process using rapid mixing and multi-stage flocculation, followed by sedimentation.

RapiSand sedimentation is extremely fast, with rise rates exceeding 13 gpm/ft², and can be applied in a wide variety of suspended solids removal applications. The typical uses of RapiSand include expanding plant capacity, minimizing plant footprint, providing fast start-up capabilities, and providing great performance characteristics. RapiSand may be the answer to your suspended solids process needs.

Need a fast and efficient solution for clarification and sedimentation? Our mobile RapiSand units can be on site at your location within days. They’re available for lease, so you can contract them for as long as you need. Visit our mobile and temporary solutions page to learn more about our fleet and services.

Process flow diagram for RapiSand

How It Works:

RapiSand ballasted flocculation is a four-step process:

1. Coagulation: Raw water is mixed with coagulant in the coagulation basin.

2. Flocculation: Coagulated water is mixed with polymer and recycled microsand in each of two flocculation basins.

3. Clarification: The flocculated water flows into the clarification basin where the floc settles and clarified water passes up through tube settlers. Clarified water exits the system by way of an outlet launder.

4. Separation: Settled floc and sand are collected and pumped to the hydrocyclone where the sand is separated from the solids. The solids are sent to waste and the separated sand is returned to the first flocculation basin.

The microsand has a specific gravity of 2.6 and is mixed with the polymer and coagulated solids to form a dense ballasted floc. Total flocculation time is typically eight minutes, which is a fraction of the time required in a conventional flocculation system. In the clarification step, the ballasted floc settles at rates that are up to 35 times faster than conventional clarification. Total detention time in the RapiSand system is typically 15 minutes from start to finish.

RapiSand can decrease the footprint of a traditional flocculation and sedimentation system by more than 95%, depending on the application.

RapiSand Ballasted Flocculation Rendering


  • Hydrofoil mixers ensure uniform mixing in all three mixing basins.
  • Circular rake system guarantees rapid transport of settled sand/solids to a centrally located hopper.
  • Industrial sand recirculation pump
  • Hydrocyclone provides separation of the microsand and flocculated solids.


  • Small footprint: RapiSand can decrease the footprint of the sedimentation system by as much as 95%.
  • Quick start-up: Plants can be operational in as little as 15 minutes from start-up.
  • Stable process: Handles large spikes in raw water turbidity.
  • Performance: Typical outlet turbidity is <2 NTU.


  • NTU/TSS Removal
  • Tertiary Phosphorus Removal
  • TOC Removal
  • Color Removal
  • CSO Treatment
  • Algae Removal
  • RO Pretreatment
  • Boiler Feed Makeup
  • Cooling Tower Makeup
  • Industrial Process Water
  • Pump Seal Water
  • Surface Water Pretreatment
  • Filter Backwash