Napier-Reid’s clarifiers provide a size and type to fit any plant requirement. The application-oriented design assures an economical performance for municipal or industrial water and wastewater treatment. Sedimentation tanks or conventional gravity clarifiers are used in water and wastewater treatment as a physical unit operation through gravity for solid-liquid separation of readily settleable solids. The functions can be further enhanced using a solid contact clarifier which combines mixing, flocculation, and clarification in a single tank.



Outstanding hydraulic design prevents short circuits provide a low scour velocity, and supplies the required effluent quality.

  • Excellent structural design guarantees years of trouble-free operation.
  • Custom designed/fabricated in order to meet the specific requirements.
  • Low operation and maintenance cost.
  • Flocculating or solid contact design available

Circular Gravity Clarifier

Conventional circular clarifiers are commonly used in municipal wastewater treatment in order to reduce BOD and suspended solids content from the wastewater prior to the main biological treatment. Typically, a well designed primary clarifier should be able to remove up to 30% of the BOD from municipal wastewater with an HRT of 30 min and a BOD concentration of 200-300 mg/L. Secondary clarification is the final process for generating a good quality effluent in numerous activated sludge processes. An adequate surface loading rate is commonly used in order to determine the clarifier area.

Circular gravity clarifiers typically have a radial flow inlet pipe that feeds into a stilling well which reduces the influent velocity and redirects it downward in order to generate a uniform flow and prevent short circuiting. A central-driven dual arm sludge collector mechanism rotates continuously over a gently slopped bottom in order to collect sludge which later falls by gravity into a steep sludge hopper. The effluent overflows through adjustable v-notched weir plates. An optional scum baffle prevents scum from flowing into the effluent channel. A skimmer mechanism can be provided for scum removal.

Circular Clarifier Mechanism Assembly

Circular Clarifier Mechanism Assembly


Clarifier with Tube Settlers

Available in circular as well as rectangular shape.

The chemically treated and flocculated feed water enters the stilling well of the clarifier. The water exits from the bottom of the stilling well and flows upward towards the weir located at the surface. The flow passes through specially designed tube-settlers.

Clarifier with Tube Settlers Marmora, Ontario, Canada

Clarifier with Tube Settlers
Marmora, Ontario, Canada


Tube settlers consist of multiple tubular channels of various shapes, sloped at an angle, generally at 60°. They combine to form an increased effective settling area. This results in reduced settling depth and hence settling time is also significantly reduced. The tube settlers increase allowable flow capacity as it increases effective settling area and solids removal rate in settling tank. Hence, clarifiers with tube settlers are more efficient and compact than conventional clarifiers.

The settled floc or sludge slide down to the tank bottom for subsequent removal. A scraper mechanism is generally provided in circular tanks to collect the settled solids and flocs for removal.


Solids Contact Clarifier

Solid Contact Clarifier - La Mesa, New Mexico, U.S.A

Solid Contact Clarifier
La Mesa, New Mexico, U.S.A

These clarifiers are used to achieve suspended solids removal in less space than conventional clarifiers. The general concept is that recycling of large quantities of flocs in the tank increases the chance of collisions of flocs. The small flocs collide and agglomerate with large flocs. As large flocs have faster settling velocity, higher flow rate per unit size of clarifier is possible compared to conventional clarifier. Solid contact clarifiers come with a central draft tube and solids contact chamber, and a recirculation pump in order to provide the required up flow rate to the previously coagulated influent.

The solids contact clarifier can be grouped into three categories: Upflow Clarifier, Reactor Clarifier, and Sludge Blanket Clarifier.

Upflow Clarifier

It is basically a sedimentation tank in which inflow enters the tank bottom or stilling well, and flows upward towards the weir located at the surface. This clarifier is designed to minimize short-circuiting of the flow, uniform withdrawal of clarified water and proper sludge removal without disturbing the settling process.

Upflow clarifiers are best suited for clarification of water with heavy, non-colloidal solids.

Reactor Clarifier

It is sometimes also known as Clari-flocculator. In reactor clarifier, coagulation, flocculation, and sedimentation processes are combined.

A typical reactor clarifier consists of circular basin design. The feed raw water enters a conical or cylindrical shaped compartment that acts as a stilling zone as well as flocculation zone. Chemicals (coagulant and flocculant) are added in this compartment. Coagulation takes place in the primary mixing zone while flocculation takes place in secondary mixing zone. The flocculation process produces a large number of particle collisions resulting in smaller particles agglomerate to form larger flocs. Water flows out from the bottom of mixing zone into the settling zone. The flocs and solids settle to the bottom and clarified water is collected over the weir at surface. The sludge settled at bottom is continuously or occasionally discarded.

Sludge Blanket Clarifier

A sludge-blanket clarifier is similar to a reactor clarifier, except that the water flowing from the bottom of the mixing zone flows through a blanket of sludge that acts as a filter. As the flocculated water passes through the suspended sludge blanket, the particles are absorbed onto the larger flocs. This increases the size and weight of the flocs and it gradually settles to the bottom and is re-circulated. When the sludge in the clarifier reaches beyond a certain level, some sludge is wasted.


Napier-Reid’s Clarifier Components

Drive Unit

  • NEMA Design B motor, totally enclosed with Class B insulation.
  • Robust in design and built with high quality components.
  • Custom sized in order to handle the specific requirements of the application.
  • Overload and current protection system included.

Sludge Collector Mechanism

  • Stainless steel or epoxy-coated steel construction for good corrosion resistance.
  • Adjustable UHMWPE squeegee plates properly designed for good scraping action.
  • All structural steel welding procedures in accordance with the requirements of the CWB- W59 “Welding of Steel Structures”
  • Arms fabricated from structural angles with a minimum thickness of 6 mm for good mechanical integrity.