Grit removal from wastewater is very important to reduce operational problems of the wastewater treatment plants and to reduce maintenance of the mechanical equipment installed in it. Grit and other solids can increase wear of the mechanical equipment, cause pipe blockages, can settle and reduce the effective volume of the treatment basins. Napier-Reid Vortex Grit Chambers (NR-VGC) are designed to separate grit from organics and raw sewage water.

Mesh Size Grit Removal
50 95% or greater
70 85% or greater
100 70% or greater

Vortex Grit Removal Process

Screened wastewater enters the NR-VGC tangentially and creates a vortex current. As the NR-VGC is designed to handle variable flow, a specially designed agitator rotates and maintains a constant rotational velocity inside the VGC chamber. Under the influence of centrifugal force and gravity, grit and other solids quickly collect to the centre of the grit chamber, enter the grit hopper, and settle down along the sloping floor.

Vortex Grit Removal Process

Vortex Grit Removal Process

Air lift pump or grit handling pumps deliver the collected grit and solids to the grit classifier for subsequent separation. The grit-free wastewater along with the organics overflow from the vortex chamber for further treatment.

Constructional Features and Advantages of Napier-Reid Vortex Grit Chambers

  • Compact design leading to smaller footprint.
  • Robust design and simple in operation.
  • Various models to cover a wide range of flow and grit handling requirements.
  • NR-VGC has a consistent grit removal efficiency over a wide range of flow.
  • High percentage of fine grit removal is possible, typically up to 70% of 100 mesh (0.14mm) size and up to 95% of 50 mesh (0.3 mm).
  • Low energy requirement due to efficient design and typical flow pattern inside the chamber.
  • Very low pressure drop across the NR-VGC, typically 6mm.
  • Designed to take advantage of tangential inflow velocity of the influent.
  • 270 degree flow pattern and baffles to prevent short circuiting.
  • Sloped grit collection hopper design eliminates grit accumulation in the vortex chamber.
  • Design provides full access to grit collection hopper.
  • Robust gear drive unit of agitator with oversized bearings for long life.
  • High efficiency electric motor suitable for rigorous conditions.
  • Well designed air lift pump for grit removal from hopper. Alternatively, grit pumps can be used for grit removal.
  • Material of construction of tank can be carbon steel or stainless steel, depending upon application or requirement. Alternate concrete tank design is available.
  • No submerged bearing or rotating part in the chamber that are subjected to wear and require maintenance.
  • Minimal maintenance.

Optional Features

  • Variable Frequency Drive (VFD) to change the speed of the agitator and optimize the process under variable flow conditions.
  • Air and/or water scouring system to remove organics, prevent grit hopper bridging, and eliminate grit removal line blocking.
  • Blower package complete with acoustic enclosures.
  • Control panel complete with PLC programming or SCADA.
Model No. VGC-40 VGC-100 VGC-150 VGC-250 VGC-350 VGC-500 VGC-750 VGC-1200
Max Flow (m3/day) 4,000 10,000 15,000 26,500 35,000 45,000 75,000 120,000
Grit Chamber Diameter (m) 1.9 2.2 2.5 3.0 3.4 3.7 5.0 6.0
Agitator (HP) 0.5 0.5 0.75 1.0 1.0 1.5 2.0 2.5

Napier Reid Vortex Grit Chambers are designed taking into consideration various operational and design parameters, some of them are as under:

  • Inlet velocity to the VGC
  • Outlet velocity from the VGC
  • Straight length to width ratio of inlet and outlet channel
  • Hydraulic loading rate
  • Detention time in the chamber
  • Size of grit to be removed
  • Settling velocity of the grit of various sizes
  • Hydraulics inside the vortex chamber to ensure there is no short circuiting
  • The flow pattern to ensure that there is minimum turbulence in the vortex chamber