Which Sludge Pump Is Most Suitable For your Water Industry Needs?
Sludge pumps, such as the Progressive Cavity, Peristaltic, Rotary lobe, Piston and specific centrifugal slurry pumps, are widely used in water treatment. Versatile, robust and hardwearing, they are used for the transportation of sludges with varying dry solids content.
Abrasive grit content is a challenge in many wastewater treatment plants, and where this is a risk careful pump selection is important.
The market for sludge pumps is diverse. Numerous brands offer different models with properties and capabilities that suit a wide range of applications. Performance, efficiency and wear-life can be tailored to the duty application by configuring motor rating, impeller design and material, adding a variable speed drive (VSD), and other modifications.
Having given an overview of common pump types used in the industry last month, let’s look at common requirements and applications in water and wastewater, the challenges they bring, and what pump solutions Atlantic Pumps would typically recommend.
Requirement: High flow, High Head Sludge Pumping
Sludge recirculation often requires a high flow rate over a certain distance or height. Usually, the pump is below the tank’s sludge level which provides a “flooded end” for the pump’s suction inlet, making it ideal for a dry-sited horizontal centrifugal pump. This arrangement makes installing and servicing the pump easier, and the net positive pressure means no priming is required between duty cycles.
Which pump brand and configuration to choose depends on the entrained solids particle size, abrasiveness, and content percentage, which affects its viscosity.
Centrifugal Pumps can be designed to suit particular sludge characteristics, here are some common sludge requirements and what pump we’d consider using for them:
Low solids percentage, low viscosity sludge – Apex Centrifugal Pump
Another British pump company, Apex Pumps specialises in centrifugal pumps and offers some highly efficient pumps for sludges at the thinner end of the scale.
If the sludge application involves extreme temperatures, such as pasteurization and other heat treatments, then Toro centrifugal pumps can prove ideal.
Toro’s centrifugal slurry pumps are capable of handling flows of up to 1000 m3/hr and heads up to 150m, and are famously low-maintenance and high-capacity. Their mechanical seal designs make them perfect for use at a wide temperature range, from cryogenic processes to above 120 °C. This makes them perfect for a range of processes in AD and CHP plants. The Toro brand was created to meet rising industry demand for a higher standard of service process pumps. As the name suggests, Toro pumps are celebrated for their powerful and robust build and thrive in heavy-duty industrial applications.
Solids Content To 6%, For High Flow Recirculation – SlurryPro Centrifugal Sludge Pump
Where grit and other abrasive solids are entrained, it is important to select a pump designed for these. The SlurryPro pump offers a longer wear life in abrasive sludge transfer, especially when fitted with rubber elastomer linings and wear-parts. For larger, sharp solids they can be fitted with high-chrome impellers to reduce the damage from heavy impacts.
Available in horizontal and vertical ranges, SlurryPro’s pumps are available in a variety of sizes from 1” (25mm) outlet diameter up to 12” (305mm).
The vertical SlurryPro is ideal for raising high volumes of sludge from well-pits and sumps, providing a dry-sited, heavy-duty alternative to submersible pump types.
SlurryPro pumps are coupled with a suitably sized motor and drive for the specific duty, and fitted with either alloy or rubber-lined materials, depending on the sludge’s properties. Single phase is available on the smaller models, although most heavy-duty industrial pumps are sold with a 3-phase, 400v rating.
SlurryPro horizontal centrifugal pumps are supplied with either an expeller-type seal, for increased time between seal replacement, or high-precision mechanical valves that eliminate leakage.
Designed with the end-user in mind, SlurryPro pumps combine robust industrial capability with a user-friendly operation. In many water treatment plants, they are connected to a control panel, or even to the ‘cloud’ for improved management. The horizontal series is perfect for easier on-site maintenance (maintain-in-place). Conversely, the vertical series is designed for effective extraction from a depth (e.g. pits and sumps), and where floor/ground space is limited.
Requirement: Submersible pump, High flow, non-clog on liquids with entrained abrasives.
Submersible Centrifugal Pumps – Audex and Flygt
Submersible, sometimes called “wet pumps” remain fully submerged in the liquid media they are pumping. This has several advantages to ‘dry pumps’ including:
• Space saving – requires less space floor space than dry-sited pumps
• Priming is not an issue, as they naturally flood
• The surrounding fluid keeps the pump from overheating
Audex and Flygt pumps commonly cover most submersible needs in water and wastewater treatment, with Audex taking the lead in challenging sludge duties and Flygt in efficiency on low-density fluids.
Founded in Sweden in 1901 by engineer and inventor Per Alfred Stenberg, Flygt claims to be the first manufacturer of industrial slurry pumps and has certainly worked hard to keep improving its designs since then.
Flygt pumps are known for their ‘self-cleaning’ capabilities with non-clog impellers and advanced sealing technologies that protect the motor against leakage. Known for their durability and versatility, they are available with a choice of hardened cast iron, duplex stainless steel and hard-iron impellers.
They are highly effective in clean water, reducing flood risk by redirecting excess water. However, they also have options for working with slurry that contains corrosive matter.
Requirement: Durable Submersible Centrifugal Pump For Agitation Of Settling Sludge, Abrasive Grits, And High Flow Rates
Audex pumps are celebrated among submersible pumps thanks to their build quality, wear resistance, and powerful agitators. These ensure heavier particles remain evenly distributed during pumping to prevent build-ups and clogging.
Frequently used for storm drainage duty, they are perfect for use in environments with very abrasive materials such as grit, and other surface run-off debris, providing efficiency and reliability where users need it most.
Audex pumps have proven to outlast many standard clean-water submersibles by four to six times on sites with abrasive, acidic or alkaline corrosive sludge.
Audex pumps are used for storm tank returns, often suspended on a pontoon, or as a heavy-duty dewatering pump in sludge tanks and pits.
Requirement: Pulsation-free Accurate Flow Or Metering. Higher Pressures, Or Suction Lift. Non-Abrasive Sludges Up To 12% Dry Solids.
Progressive Cavity Pump
Progressive cavity (PC) pumps are used extensively across wastewater sludge treatments, as they are capable of moving very viscous sludge and can achieve high pressures. Like other positive displacement (PD) pumps, the flow rate can be closely controlled by changing the running speed.
Something to bear in mind is that like most other PD pumps, models made for smooth, non-abrasive sludge can prove very costly when run with abrasive grits and sharp solids. For pumps that rely on tight tolerances (including PC, ram and lobe pumps), worn edges can quickly increase energy consumption or reduce flow-rate.
The Toro-Kronoa line of progressive cavity pumps is built to deal with thick sludges and dense slurries that contain abrasive solids. Their short-pitch design, multiple access panels, cardan-shaft, and wear-resistant surfaces lend them to challenging slurries often found in waste food processing and mixed-feed anaerobic digestion (AD) plants.
Pump Requirement: Abrasive sludges Over 12% Dry Solids With High Rag Content, Low Energy Consumption, Small Footprint, Easy Maintenance And Can Take Some Dry Running
Peristaltic Pumps
Peristaltic, also known as Hose pumps, have traditionally been rare in the water treatment industry, apart from smaller models used for dosing chemicals.
However, there is one brand of peristaltic which stands out for its potential in industrial water applications. The LSM is a Danish-made range of pumps which includes the world’s largest peristaltic-type pump. In the right applications, these have been shown to drastically reduce maintenance time and budget, increase the range of sludges treated, and increase energy efficiency at a number of wastewater and sludge treatment plants, as this example in Cumbria shows.
Where a level of pulsation can be dealt with (dampeners are available), the LSM is proving its worth in abrasive grit sludge applications. Characterised by their efficiency, known for their low energy consumption and easy maintenance alongside their outstanding build quality, LSM can pump a wide variety of sludges up to 12% dry solids, with a long MTBM (mean time between maintenance).
Highly viscous sludges can cause random supply-side gaps, resulting in dry-run damage to many pump types. The LSM peristaltic is unique in its ability to safely dry-run during these intervals. It can also be run in reverse – handy for emptying the vessel it usually fills, such as when the tank requires degritting and cleaning. The party trick of the peristaltic is its ability to handle high ‘rag’ content. With no rotating parts exposed to the sludge, it resists the wrapping and re-weaving of rag fibers allowing them to pass through the pump.
The right pumping solution can boost your treatment plant’s operational efficiency, improve productivity, eliminate downtime and reduce costs. Atlantic Pumps offers hydrological and mechatronic engineering support, sludge handling consultancy, pump system builds, and a hire service for pilot trials.
To see how we can help you optimise your process, share your slurry pumping challenge with our experts by phone, webchat or email.
