Pumps for water and wastewater treatment

A treatment plant moves clean water, raw sewage, thick sludge, aggressive chemicals and high-pressure membrane feed, often within the same plant. A pump that suits one of these fails quickly on another. Most pump problems in plants, such as blocked impellers, seal leaks, worn rotors and cavitation, come from choosing the wrong type for the liquid, not from poor quality. Below is each type, what it handles, and where it belongs in a plant.

End-suction pumps

The general-purpose pump for transfer, filter feed, backwash, treated-water supply and cooling water. Simple, easy to maintain and available in a wide range of flow and head. Not suited to raw sewage or liquids with long fibres.

Inline pumps

Fitted directly in the pipeline, saving floor space. Used for booster duty, recirculation and treated-water supply.

Horizontal multistage pumps

Several impellers in series for higher pressure. Used for filter feed against high head, booster sets and as feed pumps for small RO systems.

Vertical multistage pumps

Compact, high-pressure pumps for RO feed, UF feed, booster sets and pressure-boosting skids. Wetted parts are usually stainless steel, with duplex grades for brackish and seawater duty.

Vertical turbine and borewell pumps

Lift water from sumps, wells and borewells. Used for raw-water intake and deep source supply.

Split-case pumps

For large flows at moderate head, such as raw-water intake and large treated-water transfer.

Non-clog sewage pumps

Open or semi-open impellers that pass solids and rags. The standard pump for raw sewage, equalisation tanks and sludge sumps. Duty and standby pumps are normal.

Vortex impeller pumps

The impeller sits out of the main flow, so solids pass without striking it. Good for stringy and abrasive material, at some cost in efficiency.

Grinder and cutter pumps

Cut solids before pumping. Used where the discharge line is small, such as pressure sewers, or where rags are heavy.

Drainage and dewatering pumps

For sump emptying, tank cleaning and storm water. Not for continuous process duty.

Submersible borewell pumps

Multistage pumps that sit in the borewell for deep water sources.

Progressive cavity (screw) pumps

A rotor turning in a rubber stator moves thick sludge gently and steadily. The standard choice for sludge feed to filter presses, decanters and belt presses, and for polymer solutions. Must not run dry.

Rotary lobe pumps

Two lobes rotate in a casing. Handle sludge, scum and viscous liquids, and can run in both directions. Easy to service without removing pipework in many designs.

Air-operated diaphragm pumps (AODD)

Run on compressed air with no motor or seal. Handle sludge, slurries, chemicals and can run dry. Flow is pulsating and air use is high, so they suit intermittent duty.

Peristaltic (hose) pumps

Only the hose touches the liquid. Handle abrasive, corrosive and shear-sensitive liquids and give accurate flow for dosing and sludge sampling. Hoses need regular replacement.

Gear pumps

For oils and viscous clean liquids, such as lubricating oil transfer or skimmed oil.

Diaphragm metering pumps

Accurate, adjustable flow for chemical dosing: coagulants, polymers, acids, caustic, hypochlorite and antiscalant. Mechanical and hydraulic diaphragm designs cover different pressure and accuracy needs.

Solenoid dosing pumps

Compact, low-flow dosing pumps for small plants and for chemicals such as hypochlorite and pH correction.

Plunger pumps

High-pressure and high-accuracy duty, including some small high-pressure RO duties.

Dosing skids

Pumps, tank, mixer, level switch and piping on one frame, ready to connect. See dosing systems.

Magnetic-drive (sealless) pumps

No shaft seal, so no leak path. Used for acids, caustic and other hazardous chemicals, in plastic or lined construction.

Self-priming pumps

Lift from drums and underground tanks without foot valves. Used for chemical unloading and priming duty.

Plastic and lined pumps

Polypropylene, PVDF and PTFE-lined pumps for aggressive chemicals such as acids and hypochlorite.

Flow and head

Required flow and total dynamic head at the duty point, including pipe friction, static lift and pressure at the delivery.

NPSH

Net positive suction head available must exceed what the pump needs, or the pump cavitates and wears out.

The liquid

Solids content and size, fibres, viscosity, abrasiveness, corrosiveness, temperature and gas content decide the pump type and materials.

Materials

Cast iron, stainless steel (304 or 316), duplex steel for brackish water and brine, and plastic or lined construction for chemicals. Elastomers such as EPDM, NBR and FKM are chosen for the chemical.

Seals

Single or double mechanical seals, or sealless pumps, depending on the hazard of the liquid.

Duty pattern

Continuous or intermittent duty, number of starts, and whether a variable frequency drive is needed for flow control.

Standby

Most plants use duty and standby pumps. We size the pair so either can carry the full duty.

Site

Indoor or outdoor, hot climates, noise, and access for maintenance and lifting.

We select and supply pumps as part of a plant or on their own, against your specification and approved make list, or we propose suitable options in the quotation. Send the liquid, flow, head and duty with the RFQ checklist. See also mechanical equipment, blowers and dosing systems.