What is a chopper pump?
Chopper pumps are centrifugal pumps with the capability to handle fluids with a high concentration of solids. Chopper pumps have a cutting attachment made of hard materials of fixed and rotating elements that macerate solids before entry to the impeller, allowing it to handle difficult materials. Solids are cut so they pass through the pump more easily and flow out with the rest of the pumped fluid.
Chopper pumps’ ability to handle solids gives them more flexibility in what they can pump. This characteristic makes them particularly useful in wastewater treatment plants. Wastewater treatment is split into primary treatment and secondary treatment. Primary treatment is the physical separation of floatable materials and insoluble solids from the wastewater. Secondary treatment is biological treatment of water using microorganisms to remove the remaining solids in the fluid. Both treatments contain solids in the pumped fluid and may require chopper pumps.
Specific steps in the process include pumping scum, mixing the contents of the aeration basin and the anoxic zone and pumping sludge. Image 1 shows an example of an aeration basin at a treatment facility where chopper pumps mix oxygen with wastewater to encourage the growth of microorganisms to break down solids.
A typical centrifugal pump impeller is more easily clogged by solids, which can halt pumping and cause damage to the system. In particular, stringy materials found in wastewater during the treatment process are especially troublesome to normal centrifugal pumps since the material can tangle the impeller. However, the chopper pump is more effective in dealing with this issue.
For more information on the application of pumps in power plants, refer to HI Guideline Wastewater Treatment Plant Pumps at www.pumps.org.