Wastewater treatment involves the removal of impurities from sewage before it reaches aquifers as well as rivers, lakes, and estuaries. The distinction between clean water and polluted water depends on the concentration of specific impurities in relation to its intended use. In general terms, water is considered polluted when enough impurities are present to make it unfit for a particular application – such as fishing, swimming, or drinking. Water pollution is mainly the result of the drainage of contaminated wastewater into the surface or groundwater. Therefore, wastewater treatment plays a significant role in the control of water pollution.
There are two basic types of pumps utilized in wastewater treatment: centrifugal and positive displacement. To make the appropriate choice, it’s essential to understand the differences between these two pumps.
Basic Operation: Centrifugal and Positive Displacement Pumps
To best understand the differences between the two types of pumps, it is necessary to understand their basic operation.
Positive displacement pumps: These pumps have three basic elements that are integral to their basic operation.
An intake valve that utilizes suction to draw liquid into the pump
An internal cavity that traps the liquid inside the pump
An outlet valve that forces the liquid from the pump.
Centrifugal pumps: These pumps are more simplistic by design. The primary mechanism of a centrifugal pump is the impeller, which rotates fluid through the pump. The impeller draws fluid into the pump and then utilizes kinetic energy to move the fluid through the pump until it exits via a discharge valve.
Pressure and Flow Rates
One of the primary advantages of a positive displacement pump is its consistent flow rate, which remains constant when there are changes in pressure. In contrast, the design of a centrifugal pump reacts to pressure changes. The peak efficiency of a centrifugal pump occurs at a specific level of pressure. When the pressure is not at this specific level, the pump’s effectiveness is diminished.
Viscosity and Flow Rates
Another notable difference between centrifugal and positive displacement pumps is the way the fluid viscosity impacts the flow rate. When utilizing a centrifugal pump, increased viscosity causes a significant reduction in flow rate. When a positive displacement pump is in use, an increase in viscosity causes an increase in flow rate. Therefore, positive displacement pumps are most appropriate for applications that handle highly viscous liquids.
Which Pump is More Appropriate for Wastewater Treatment?
Centrifugal pumps are best utilized to process a large amount of low-viscosity fluid in a low-pressure setting. It is most appropriate for transferring water, but it is also a good choice for transferring low-viscosity fuels and chemicals.
Centrifugal pumps can be made of plastic, stainless steel, or cast iron. Because the design can be adjusted for different needs and applications – and is also compact enough for smaller operations – it is considered a versatile choice.
Positive displacement pumps are most often utilized for pumping sewage, oil, and slurry (a mixture of denser solids suspended in liquid). These pumps are an excellent option for pumping fluids that contain solid materials, as well as in situations when there will be changes in pressure since the flow rate will remain consistent. It is widely considered to be a smart choice for wastewater treatment applications.
To learn more about centrifugal and positive displacement pumps, browse the Zwirner Equipment inventory here – then call us for more information. Remember, if you don’t see what you need, we are here to help you source the equipment you require.
Click here to view the current inventory of centrifugal pumps.
Click here to view the current inventory of positive displacement pumps.
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