Sewage & Wastewater Pumps: Types, Impellers & Selection Guide

Quick Answer

Sewage and wastewater pumps are solids-handling centrifugal pumps designed to move liquids containing rags, fibres, grit, and debris without clogging. The three main configurations are submersible (the pump sits in the wet well, submerged in the liquid — the dominant modern choice, compact, quiet, no pump room needed), dry-pit (the pump sits in a dry chamber beside the wet well, easier and safer to maintain), and self-priming (mounted at grade above the wet well, drawing liquid up — simplest access, but limited by suction lift). Performance is determined mainly by the impeller type: vortex (recessed) impellers create a swirling flow so solids pass without touching the impeller — best clog resistance, lowest efficiency; single-channel impellers give large solids passage with good efficiency; multi-channel impellers offer higher efficiency and lower vibration but smaller solids passage; grinder pumps shred solids before pumping, enabling small-diameter discharge; chopper pumps cut solids at the intake for heavy debris and sludge. The dominant modern problem is ragging — wet wipes and fibrous material wrapping the impeller — which has made non-clog and self-cleaning impeller designs essential. Selection balances required solids passage, hydraulic efficiency, wet well design, and the real debris content of the sewage.

Few pumps work in worse conditions than a sewage pump. It handles a liquid that is corrosive, abrasive, biologically active, and full of things that were never meant to be pumped: rags, wipes, plastic, grit, grease, and fibres. It often runs unattended in an underground wet well, starting and stopping thousands of times a year. And when it fails, the consequence is not lost production but sewage backing up into streets or buildings.

The engineering challenge has actually grown harder over the last decade. The spread of so-called "flushable" wet wipes has transformed the debris profile of municipal sewage — fibrous material that does not break down, wraps around impeller vanes, and builds into ropes that block the pump. This phenomenon, known as ragging, is now the single most common cause of sewage pump failure, and it has driven a generation of non-clog and self-cleaning impeller designs.

Selecting a sewage pump well therefore means thinking less about hydraulic efficiency alone and more about what actually goes through the pump. A highly efficient closed impeller that clogs every fortnight costs far more in call-outs than a slightly less efficient vortex impeller that never blocks.

For municipal engineers, wastewater plant operators, consultants, and contractors — this guide covers sewage and wastewater pumps: the configurations, the impeller types that determine clog resistance, materials, wet well and system design, and how to select for real-world debris.

For general pump theory, see Centrifugal Pumps and Submersible Pumps.

Pump Configurations

Submersible Sewage Pumps

The pump and motor are sealed in a single unit that operates submerged in the wet well, typically on a guide-rail system with an automatic discharge connection so the pump can be lifted out without entering the well.

• The dominant modern configuration for lift stations and pumping stations
• No separate pump room or building needed — lower civil cost
• Quiet (liquid dampens noise), no odour issues from a dry chamber
• Self-cooling via the surrounding liquid (or with cooling jackets for dry-run capability)
• Requires lifting equipment for maintenance; motor is a sealed unit

Dry-Pit (Dry-Well) Pumps

The pump sits in a dry chamber adjacent to the wet well, connected by suction piping.

• Easier and safer routine maintenance — operators access the pump without confined-space entry into sewage
• Better for large stations where pumps need frequent attention
• Higher civil cost (two chambers), requires ventilation and drainage
• Some models are submersible-type pumps installed dry with cooling jackets

Self-Priming Pumps

Mounted at grade above the wet well, drawing liquid up through a suction line.

• Simplest access — everything at ground level, no confined space entry, no lifting gear
• Popular for smaller municipal stations and industrial duties
• Limited by suction lift (practical limit typically around 6–7.5 m and reduced by debris and temperature)
• Requires priming chamber maintenance and a good foot/check arrangement

Configuration Comparison

Impeller Types — The Critical Choice

The impeller determines clog resistance, solids passage, and efficiency. This is the most important sewage pump decision.

Vortex (Recessed) Impeller

The impeller is recessed into the back of the casing. It spins the liquid into a vortex, and solids pass through the open casing volume without contacting the impeller vanes.

• Best clog resistance of any design — solids and long fibres pass freely
• Handles stringy material, rags, and wipes better than any other impeller
• Lowest hydraulic efficiency (typically 35–55%) — higher energy cost
• Choose when debris is severe and reliability outweighs efficiency

Single-Channel (Single-Vane) Impeller

One curved vane forms a single large passage through the impeller.

• Large solids passage — commonly passes spherical solids up to 100 mm+
• Good efficiency (typically 60–75%)
• Inherently unbalanced (one vane), so vibration is higher; requires robust bearings
• The general-purpose municipal sewage workhorse

Multi-Channel (Two/Three-Vane) Impeller

Two or three vanes forming multiple passages.

• Higher efficiency (up to ~80%) and smoother, better-balanced running
• Smaller solids passage than single-channel
• Best for treated effluent, storm water, and applications with limited large debris
• More prone to ragging in raw sewage

Self-Cleaning / Non-Clog Impellers

Modern designs with swept-back leading edges, relief grooves in the wear plate, and open channels that shed fibrous material rather than trapping it.

• Developed specifically to combat wet-wipe ragging
• Combine good efficiency with strong anti-clog performance
• Increasingly the default specification for new municipal stations

Grinder Pumps

A cutting mechanism shreds solids into a slurry before they enter the pump.

• Enables small-diameter pressure discharge (as small as 32–50 mm) instead of large gravity sewers
• Used in low-pressure sewer systems, individual property connections, and difficult terrain
• Higher power draw and cutter wear; not for high volumes

Chopper Pumps

Heavy-duty cutting elements at the pump intake chop solids as they enter.

• For the heaviest debris — sludge, manure, industrial waste, screenings
• Handles material that would defeat any non-clog impeller
• Robust and power-hungry; used in treatment plants, agriculture, and industrial waste

Impeller Selection Summary

Materials

Sewage is corrosive and abrasive, and hydrogen sulphide in septic conditions attacks both metals and concrete.

• Cast iron (EN-GJL / GG25) — standard casing and impeller material, economical
• Ductile iron — higher strength for larger units
• Hardened / high-chrome iron — for abrasive grit-laden duty
• Stainless steel (316) — corrosive industrial effluent, saline or chemical waste
• Duplex — aggressive chloride-bearing effluent
• Coatings — epoxy and ceramic-filled coatings extend life in abrasive and corrosive service
• Mechanical seals — double seals in an oil chamber (silicon carbide faces) are standard for submersible sewage duty; SiC/SiC resists abrasive wear far better than carbon

Wet Well and System Design

Pump selection is only half the job — many "pump problems" are actually system problems.

Wet well sizing: must balance adequate storage against retention time. Too small and the pump short-cycles (motor overheating, premature failure); too large and sewage becomes septic, generating H₂S, odour, and corrosion. Follow manufacturer minimum cycle times and check starts per hour against the motor rating.

Benching and fillets: sloped floors prevent solids settling and accumulating in dead corners.

Inlet arrangement: the incoming flow should not cause vortexing, air entrainment, or turbulence at the pump intake.

Minimum submergence: must be maintained at the lowest operating level to prevent air entrainment.

Discharge velocity: maintain roughly 0.8–1.0 m/s minimum in the rising main to keep solids in suspension and prevent settlement — an oversized rising main silts up.

Check and isolation valves: each pump needs a check valve (typically a swing or ball check suited to solids) and an isolation valve. Standard check valves designed for clean water clog on rags — specify solids-handling designs. See Check Valves.

Duty/standby arrangement: most stations use duty/standby or duty/assist pumps with alternating control so wear is shared and a failure does not stop the station.

Level control: float switches, ultrasonic, or hydrostatic level sensors; ultrasonic avoids contact with debris but needs clear line of sight.

Common Specification Mistakes

After 15+ years supplying pumps and industrial equipment to municipal and industrial projects:

Mistake 1: Selecting on Efficiency Alone

Multi-channel closed impeller chosen for best efficiency in raw sewage. It rags with wipes and blocks repeatedly; call-out costs dwarf the energy saving.

Prevention: Match impeller type to actual debris content. In raw municipal sewage, prioritise clog resistance — vortex or modern self-cleaning designs — over peak efficiency.

Mistake 2: Undersized Solids Passage

Pump specified without checking free solids passage against the sewer's debris. Solids that pass the sewer cannot pass the pump.

Prevention: Specify minimum free spherical solids passage (commonly 80–100 mm for municipal raw sewage) and verify against the pump curve data.

Mistake 3: Wet Well Too Small — Short Cycling

Wet well sized for space rather than pump cycle time. The pump starts and stops constantly, overheating the motor and destroying it early.

Prevention: Size the wet well for the manufacturer's minimum cycle time and maximum starts per hour.

Mistake 4: Oversized Rising Main

Rising main sized generously "for future capacity". Velocity falls below the self-cleansing threshold, solids settle, and the main silts up.

Prevention: Size the rising main for a minimum velocity around 0.8–1.0 m/s at duty flow.

Mistake 5: Wrong Check Valve

Clean-water check valve fitted on a sewage discharge. Rags catch on the disc and hold it open, allowing backflow.

Prevention: Use solids-handling check valves (full-bore swing or ball check) designed for wastewater.

Mistake 6: Ignoring H₂S Corrosion

Standard materials and coatings used in a station with long retention times. Hydrogen sulphide attacks the pump, guide rails, lifting chain, and concrete.

Prevention: For septic conditions, specify corrosion-resistant materials and coatings, stainless guide rails and chain, and address retention time in wet well design.

Mistake 7: No Standby Pump

Single pump installed to save cost. When it clogs or fails, the station overflows.

Prevention: Provide duty/standby (or duty/assist) with automatic alternation for any station where overflow is unacceptable.

Supply from Kasko Makine

Kasko Makine supplies sewage and wastewater pumps and pumping station equipment for municipal, industrial, and infrastructure projects:

Pump types:

• Submersible sewage pumps (guide-rail and free-standing)
• Dry-pit sewage pumps
• Self-priming wastewater pumps
• Grinder pumps
• Chopper pumps
• Storm water and drainage pumps
• Sludge and effluent transfer pumps

Impeller options: vortex (recessed), single-channel, multi-channel, self-cleaning non-clog, grinder, chopper

Materials: cast iron, ductile iron, high-chrome abrasion-resistant iron, 316 stainless, duplex; epoxy and ceramic coatings; SiC/SiC double mechanical seals

Station equipment: guide rail systems, discharge connections, lifting chains and stainless hardware, level controls, control panels with duty/standby alternation, check and isolation valves, penstocks

Engineering support:

• Duty point sizing and pump curve verification
• Impeller selection for actual debris content
• Wet well sizing and cycle time calculation
• Rising main velocity check
• Material selection for corrosive and abrasive effluent
• Duty/standby configuration and control philosophy

Certification: EN 10204 Type 3.1, performance test curves, IP68 rating and motor certification, ATEX where required

Logistics: Sewage pumps shipped from Istanbul to projects across Africa, the Middle East, Central Asia, and beyond. Standard pumps 6-10 weeks; large and specialty units 12-20 weeks; complete station packages by project schedule.

Need sewage or wastewater pumps? Send us your duty point (flow and head), effluent description (raw sewage, storm water, industrial, sludge), expected debris and solids size, station configuration (submersible, dry-pit, self-priming), and wet well details to info@kaskomakine.com or WhatsApp +90 (537) 521 1399. We'll recommend the impeller type for your debris profile, size the pump, review the station design, and provide a quotation within 48 hours.

Continue Reading: Pump Guides

• Industrial Pumps Guide — All pump types and how to choose
• Submersible Pumps — Submersible applications
• Centrifugal Pumps — Working principle, NPSH and BEP
• Positive Displacement Pumps — Sludge and viscous alternatives
• Check Valves — Solids-handling discharge valves

Frequently Asked Questions

Q: What type of pump is used for sewage?
A: Sewage is pumped with solids-handling centrifugal pumps in three main configurations. Submersible pumps sit in the wet well submerged in the liquid, usually on a guide-rail system with automatic discharge connection — this is the dominant modern choice because it needs no separate pump room, is quiet, and has lower civil cost. Dry-pit pumps sit in a dry chamber beside the wet well, giving safer and easier maintenance access without confined-space entry, at higher civil cost. Self-priming pumps mount at grade above the wet well and draw liquid up, offering the simplest access but limited by suction lift (typically around 6–7.5 m). The impeller type — vortex, single-channel, multi-channel, grinder, or chopper — determines clog resistance and is the most important selection decision.

Q: What is a vortex impeller and when should it be used?
A: A vortex (recessed) impeller sits recessed into the back of the pump casing so that it spins the liquid into a vortex and solids pass through the open casing volume without contacting the impeller vanes. This gives the best clog resistance of any impeller design, handling stringy material, rags, and wet wipes far better than channel impellers. The trade-off is hydraulic efficiency, typically 35–55%, which is significantly lower than channel impellers and means higher energy cost. A vortex impeller is the right choice when debris is severe and reliability matters more than efficiency — for example, raw municipal sewage with heavy wipe content, or any station where call-out costs for clearing blockages would exceed the energy saving.

Q: Why do sewage pumps clog with wet wipes?
A: Wet wipes and similar fibrous materials do not break down in sewage the way paper does. When they reach a pump, the fibres catch on the leading edges of impeller vanes and on the gap between impeller and wear plate. Once caught, more material accumulates on the same point, twisting into ropes that progressively block the impeller passage — a phenomenon known as ragging. Closed multi-channel impellers are most vulnerable because they have several vane leading edges and narrower passages. Prevention comes from impeller selection: vortex impellers avoid contact between solids and vanes entirely, while modern self-cleaning non-clog impellers use swept-back leading edges and relief grooves in the wear plate to shed fibrous material instead of trapping it.

Q: What is the difference between a grinder pump and a chopper pump?
A: Both cut solids, but for different purposes. A grinder pump has a cutting mechanism that shreds solids into a fine slurry before they enter the pump, which allows the discharge to use small-diameter pressure piping (as small as 32–50 mm) instead of large gravity sewers. Grinder pumps are used in low-pressure sewer systems, individual property connections, and difficult terrain where gravity sewers are impractical. A chopper pump has heavy-duty cutting elements at the pump intake that chop solids as they enter, sized for the heaviest debris — sludge, screenings, manure, and industrial waste that would defeat any non-clog impeller. Chopper pumps are used in treatment plants, agriculture, and industrial waste handling. Both draw more power than standard non-clog pumps and have wearing cutter components.

Q: How do you size a sewage pump wet well?
A: Wet well sizing balances two opposing requirements. Too small a well causes the pump to short-cycle — starting and stopping frequently, which overheats the motor and causes premature failure — so the well must provide enough working volume to satisfy the manufacturer's minimum cycle time and maximum permitted starts per hour. Too large a well gives excessive retention time, allowing sewage to become septic and generate hydrogen sulphide, which causes odour and corrodes the pump, guide rails, lifting chain, and concrete structure. The well should also have benched, sloped floors to prevent solids settling in dead corners, an inlet arrangement that avoids vortexing and air entrainment, and adequate minimum submergence at the lowest operating level.

Q: What solids size should a sewage pump pass?
A: Free spherical solids passage for raw municipal sewage is commonly specified at 80–100 mm or larger, and the pump must pass anything that can pass through the incoming sewer. Single-channel impellers typically achieve the largest passage, commonly 100 mm and above, which is why they are the general-purpose municipal workhorse. Vortex impellers also pass large solids well because material travels through the open casing volume. Multi-channel impellers offer smaller passage and suit storm water and treated effluent rather than raw sewage. Always verify the stated free passage against the pump manufacturer's curve data rather than assuming it from the discharge size, and consider the debris profile — long fibrous material can bridge and block a passage that a sphere of the same nominal size would clear.