The Otay River Pump Station (ORPS), which pumps 7 to 9 millions of gallons per day (mgd) of raw sewage to the South Bay Water Reclamation Plant for water recovery, had a problem in the 50-foot long by 10-foot wide by 30-foot deep wet well. A floating blanket of grease and debris, sometimes as thick as 4 feet, would occur on a regular basis.
Image 1. An example of a chopper pump. (Image courtesy of Vaughan Company)The City of San Diego had been contracting two vacuum trucks to clean out the station every three to four months at a cost of approximately $50,000 to $100,000 per year. Since the city has had good experiences replacing their clogging non-clog pumps with chopper pumps, they turned once again to a chopper pump company for a more cost-effective solution.
Chopper pumps can be ideal for use in pump stations and lift stations as conditioning pumps. When used as a conditioning pump, a submersible chopper is fitted with a nozzle to provide high-velocity mixing and is placed in the problem wet well on a portable stand.
The purpose of the conditioning pump is to recirculate and chop the contents of the wet well. Recirculating the wet well contents through a chopper pump chops and mixes the grease and debris that can accumulate as a floating layer, and chops and re-suspends heavier debris that can accumulate on the wet well floor.
This homogenization of the wet well contents not only prevents buildup of grease and debris in the wet well, but also helps prevent clogging of the non-clog pumps typically used as dewatering pumps for these stations.
For ORPS, the chopper pump company selected an 8-inch submersible chopper pump with a 25 horsepower (hp), 1,200 rotations per minute (rpm) motor with mixing nozzle and portable stand. In 18 months of use with the conditioning pump, the wet well has not required cleaning. Based on the cost of the pump and installation, the pump paid for itself in just two-and-a-half months of use.
Chopper Pump Applications
In San Diego, a submersible chopper pump was used in pump stations and lift stations. A chopper pump can be used in many industries and applications, including:
- Wastewater handling, including raw sewage, septage, clarifier scum pits, return and waste-activated sludges, and digester mixing
- Food processing, where chopping and pushing through byproduct elements that can clog a system, including feathers, fat and other organic materials is required
- Automotive and steel industries, to handle byproducts including metal chips, oil washdown and iron ore pellets
- Contractor businesses, to handle hazardous waste and storage tank cleanup
- Chemical and petrochemical facilities, to disperse latex skins and sulfur froth, keep storm drains clear
- Other industries, such as sand and gravel, steel, paper and wood products.