How to Choose the Right Sludge Pump

Sludge is categorized as a semi-solid slurry resulting from different industrial processes, particularly wastewater treatment and sanitation systems. Essentially sludge is a settled suspension, often stemming from processes used to treat water or from septic tanks and pit latrines. Sometimes the term sludge is used generically for solids separated from a liquid suspension that contains a significant amount of fluid between solid particles.

Other wastewater from industrial processes can also produce sludge, such as from making food and beverages. As such, it often contains significant nutrients like protein that can be used in animal feed production. Whatever the process produces it, there must be a means to transport the sludge. Pumps fulfill this role, moving sludge to where it can be properly disposed of or processed into useful material. 

Choosing the Right Industrial Sludge Pump 

Sludge pumps must be capable of transporting waste solutions containing significant solids. Due to the similarities between slurry and sludge, pumps designed for these purposes are often interchangeably called slurry or sludge pumps. Whether a slurry or sludge, pumps for this purpose require enormous power due to the heavier weight of the waste liquids they move. Sludge pumps must also deal with fluids containing material that corrodes and can be toxic or volatile.

The heavier the sludge, the more horsepower a pump requires. Various considerations must also be considered, such as the material out of which a sludge pump is made, the size and design of the pump’s impellers, how it discharges, and various other factors. To choose the best sludge pump for an application, it’s important to seek expert advice to ensure the pump performs its job efficiently and effectively.

Industrial Sludge Pumps & Their Uses

Sewage from municipalities is a primary source of sludge. Pumping this sewage sludge into and through treatment facilities means moving solids within the wastewater. These include human excrement and urine, inorganic solids, food waste, organic waste, microorganisms, and even traces of chemicals, among other contents. These solids within the sludge are referred to as wastewater solids. Once treated and transformed into biosolids, they can be used as fertilizer instead of incinerated or taken to landfills.  

Industrial facilities also produce sludge. Pumping waste from food processing facilities, petrochemical plants, paper manufacturers, and other industrial facilities involves a process very similar to transporting municipal sewage. Though certain types of industrial sludge can drain into municipal sewage systems, it’s sometimes delivered separately to a wastewater treatment facility because of the sometimes toxic content within industrial sludge.

Regardless of how it reaches a facility, sludge is treated to:

• Decrease dangerous pathogens within the sludge to lessen health hazards to people and the environment.
• Gather useful byproducts from the treatment process that can be sold or utilized to allay costs.
• Keep harmful gases from being emitted by organic matter within the sludge.
• Reduce the volume of sludge and, in so doing, lower handling costs.

Offsetting costs is often done by collecting useful byproducts or reducing sludge volume. Though sludge often accounts for less than half a percent of most material processed by wastewater treatment facilities, as much as half the plant’s operational costs can be expended on processing sludge.

Sludge Pumps in Water Treatment

Because of the stench it emits and the tendency to contain microorganisms that can cause disease, sludge has been treated since the late 19th century. Sludge pumps are integral to modern-day water treatment. Once sludge is separated from the sewage, its raw form makes it potentially dangerous to the natural environment. It can even directly affect the health of communities. These days, sludge is seen as a potential resource, with peristaltic pumps – a type of positive displacement sludge pump – used to transport the nutrient-rich sludge to an anaerobic digester for treatment. This process creates a product that can be added to soil to make it more productive.

The Difference Between Slurry & Sludge Pumps

The difference between a slurry and sludge pump isn’t so much about the pumps and how they operate but concerns the material they must transport. Texture and consistency are the main differences between slurry and sludge. Pumps for slurries or sludge need to transport both organic and inorganic solids within the fluid. However, sludge is more viscous and thicker, while the slurry is thinner, so flows more easily. Because of this, sludge pumps need to employ more power to carry the thicker liquid and prevent the system from clogging.

Types of Sludge Pumps

Two main types of pumps are used for sludge. Pumps for transporting sludge are usually of the centrifugal variety, though positive displacement sludge pumps are sometimes preferred for certain applications, such as for anaerobic water treatment. Centrifugal sludge pumps convert electrical energy into kinetic energy through a rotating impeller. This kinetic energy then creates pressure, causing the sludge to flow. Though flowrates for centrifugal sludge pumps can reach hundreds or even thousands of gallons per second when handling sludge containing smaller particles like sand, these pumps only produce a pressure of about 1000 psi (pounds per square inch).

In contrast, positive displacement sludge pumps operate differently. Positive displacement pumps increase pressure intermittently and add energy to produce a faster sludge flow. Pumping at higher pressures than centrifugal pumps, positive displacement pump flowrates can only reach about 250 gallons per second though they can handle pressures of up to 70 thousand psi. 

Positive displacement sludge pumps are either reciprocating or rotary in nature. Reciprocating sludge pumps often have a piston or plunger design, while examples of rotary sludge pumps are rotary vane vacuum pumps or progressing-cavity pumps, the latter of which can handle sludge comprised of 40 percent solids by weight. Reciprocating sludge pumps are used only when a considerable quantity of sludge needs to be moved, as reciprocating pumps are complicated to maintain and have higher startup costs.

For smaller amounts of sludge, pumps that use compressed air can be used instead to transport sewage. For example, air pressure pumps or pneumatic ejectors can be used for this purpose. These pumps are quieter and have fewer moving components, so they are less likely to experience blockages than larger-capacity sludge pumps. However, these options are far less efficient.

Ask Hayes About Which Sludge Pump is Right for Your Application

Hayes Pump distributes sludge pumps throughout the Northeast from various manufacturers. To learn more about which sludge pump would work best for your application or to learn more about our other products and services, contact the pump experts at Hayes.