Sludge Pumps & Slurry Pumps: Everything You Need To Know

Sludge, slurry and sewage—three topics that aren’t a subject of everyday “pleasant” conversations. Any of these words conjures images of yucky goo, germs, and debris. But dealing with these fluids is a fact of life, and you need the right kind of submersible pump to handle the heavier load. 

Having the right pump helps considerably with handling sludge and slurry safely. But with many brands and types of pump on the market, what kind of heavy-duty pump do you need to handle the workload?

Sludge pumps and slurry pumps are often considered interchangeable, but they do have slightly different functions. Both sludge and slurry are fluids with a high percentage of solids, but sludge is softer and thicker. Slurry is thinner and flows through the pipes more easily. 

This article explains everything you need to know about sludge and slurry pumps, including the difference between a sludge pump and a slurry pump, and when you might need one. 

Read on to understand the differences between sludge and slurry and the types of pumps that are designed to work with them.

What is Sludge?

Sludge is a thick, viscous liquid that’s made up of organic and inorganic materials. It’s typically produced during the wastewater treatment process, ranging from sewage treatment to industrial byproducts. 

Sludge can be composed of a number of different materials, including:

• Organic materials: These are the most common type of sludge and include things like food waste, paper, and plant matter.
• Inorganic materials: These are the non-biodegradable materials that can be found in wastewater, such as metals, plastics, and solvents.

Sludge has a thick texture that may be very viscous or sticky, making it difficult to pump. However, with a higher percentage of solids, it is more compact and can facilitate the disposal of waste products. 

What is Slurry? 

Slurry is a water-based mixture that contains solids in suspension. It’s commonly generated in industrial, mining and agricultural settings. Slurry is thin and sloppy, and flows more easily than sludge. 

Slurry can be made up of a number of different materials, including:

• Solids: These are the insoluble materials that are found in the liquid. They can be in the form of particles, flakes, or pellets
• Liquids: These are the materials that help to suspend the solids. They can be in the form of water, wastewater, or other liquids.

Being easier to pump, slurry is the preferred output where waste needs to be transported in liquid form. Being distributed in a liquid suspension, slurries can make it easier to relocate and dispose of waste products in the mining and construction industries. 

Are Sludge and Slurry the Same Thing? 

Both sludge and slurry are mixtures of liquid and pulverised solid waste, but they are not the same. Sludge has a heavier consistency, like thick mud, while slurry is thinner and less viscous. 

The main difference between sludge and slurry is the texture, rather than the composition of the fluid. Both slurry and sludge contain solids such as sand, mud, metals, sediments, and other particles within the liquid. They may be organic (like sewage) or non-organic. 

Sludge is a thick and viscous fluid, and may be sticky, while slurry is thinner and flows more easily. This means that pumping requirements can vary significantly between these two fluids, and is also influenced by the type of particles found in the material. 

Both sludge and slurry are often industrial byproducts, meaning that liquid might also contain certain acids, alcohols, oils, or other solvents. Therefore, both sludge and slurry need to be correctly and responsibly disposed of, considering the environmental impact and local regulations.  

What Is a Sludge Pump?

The purpose of the sludge pump is to move sludge through sewer lines or other systems. Sludge can be heavy and often abrasive and corrosive; therefore, these pumps need to be high-powered. The heavier the sludge, the more horsepower that is required.

There are two main types of sludge pumps: centrifugal (or dynamic) pumps and positive displacement pumps.

Centrifugal pumps are commonly used thanks to their ability to pump effluent reliably. A centrifugal pump consists of a rotating impeller that converts electrical energy from the motor into kinetic energy. The kinetic energy is then converted to pressure, which creates the flow of the sludge through the pump. 

These pumps can handle particles up to the size of sand, and flow rates can go as high as thousands of litres per second. However, these pumps cannot generate pressures higher than 1000 psi. 

Positive displacement pumps work differently. While centrifugal pumps use continuous energy to increase the sludge flow, positive displacement pumps work by intermittently adding energy to increase pressure. They can generate more pressure than centrifugal pumps, but their flow rate can only go up to nine hundred and fifty litres per second.

There are two designs for the positive displacement pumps: either reciprocating (such as the plunger and piston design) or rotary (progressing-cavity pumps and rotary vane vacuum pumps being examples).  

What Is a Slurry Pump?

Slurry pumps are the type of pumps that are appropriate for pumping slurry. Choosing the suitable pump will depend on the size and types of solids in the slurry liquid and how corrosive the slurry mixture is. The larger and more corrosive the slurry is, the more heavy-duty the pumps would need to be.

Like sludge pumps, the two most common types of slurry pumps are centrifugal pumps and positive displacement pumps. 

Centrifugal pumps are mainly used for slurry at concentrations less than seventy percent solid by weight; and come in various appearances, such as horizontal, submersible, and vertical. 

Positive displacement slurry pumps are more limited when it comes to capacity, but they are better for pumping slurry with higher concentrations of solid material.

Centrifugal pumps, such as Bianco Vulcan centrifugal pump are above ground pumps that can be added to existing pump lines to add more power and suction force to the set up. In comparison, submersible drainage pumps such as the Nova submersible pump are powerful pumps ideal for removing water from an area, either on a daily basis or in case of emergencies. 

Positive displacement slurry pumps are more limited when it comes to capacity, but they are better for pumping slurry with higher concentrations of solid material.

How Are Sludge and Slurry Pumps Different From Water Pumps?

Water pumps differ from slurry or sludge pumps. The viscosity and composition of these fluids mean they need much higher pressure and hydraulic capacity than water pumps. Finally, water pumps cannot withstand potential chemical corrosion and particle abrasion.

Sludge and slurry both contain solid particles, including (but not limited to) sand, gravel, and metals; the difference lies in their consistency. Furthermore, while the liquid in sludge and slurry can indeed be water, it can also contain other types of liquid such as petroleum and various acids.

Due to the difference in viscosity and composition of slurry and sludge, installing and using the correct type of pump is imperative.

For pumping slurries, a centrifugal pump or heavy-duty drainage pump is used.

For pumping sludges, positive displacement pumps such as diaphragm pumps, lobe pumps, and Moyno pumps are best.

Do I Use a Sludge Pump or Slurry Pump for Sewage?

A sludge or slurry pump can be used to pump out sewage from sewage lines. The most common type of pumps used for sewage are centrifugal pumps. These pumps can effectively push sewage and can be installed in pits and sumps. 

Due to their higher starting costs and complex maintenance, reciprocating pumps are less common than centrifugal pumps. Reciprocating pumps are used in specialised cases when a larger-than-normal quantity of sewage needs to be pumped.

If you are dealing with a small amount of sewage that doesn’t justify the need to construct a pumping station, you can use air pressure pumps or pneumatic ejectors. Unlike other pumps with spinning impellers or pistons, these pumps use compressed air to move sewage. These small-capacity pumps are quieter, have fewer moving parts, and develop blockages less frequently. However, they are the least efficient among the pumping options available. 

Are Slurry Pumps and Sludge Pumps Submersible?

Because there are several conditions where a slurry pump or a sludge pump is called for, there are three types of installations to consider: dry installation, semi-dry installation or wet installation, which involves fully submerging the pump. 

First is a dry installation where the bearings and the pump drive are kept out of the sludge or slurry. The wet end—which may include the impeller, suction liner, shaft sleeve, and shell—is free-standing and out of the way of any liquid. Horizontal slurry pumps are mostly dry installations.

The second method is semi-dry installation. The operator floods the wet end and the bearings but keeps the drive dry. This installation is often used for dredging with horizontal pumps.

The final method is wet installation. Using this method, the slurry pump and drive are fully submerged. Wet installation is often reserved for underwater operations, cement plants, dyeing and printing plants, and similar industries. The pumps used are often vertical centrifugal pumps with semi-open impellers.

Related Questions

What Does It Mean When a Pump Is Cavitating?

A pump is cavitating when the liquid in the pump turns to vapour at low pressure. Cavitation happens when voids (or bubbles) form within the slurry because the pressure rapidly decreases below the vapour pressure. 

How Far Can Sewage Be Pumped?

Sewage ejector pumps can pump high volumes of sewage to a maximum of about230 metres. Septic grinder pumps are better for low volumes but can pump sewage a much longer distance. 

What Type of Pump Is Best for Wastewater Pumping?

The type of pump needed depends on the type of wastewater that needs to be pumped. Centrifugal pumps are good for sludge wastewater with less particulates or solids. Rotary lobe pumps are great for thicker or more viscous fluids. Progressive cavity pumps and the air-operated diaphragm pumps are also suitable for sludge.

Can You Pump Mud?

While it is possible to pump mud, it’s difficult and complex, so it requires specialised equipment. A reciprocating piston-driven or plunger-driven pump specially made to pump mud is needed for the task, and these can be expensive.

Can I Install a Slurry Pump Myself?

It’s best to have a pump professionally installed by a licensed specialist. Slurry pumps are intricate systems that won’t work correctly if not installed properly. To avoid issues with your slurry pump system, we always recommend getting it professionally installed.