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The Otay River Pump Station (ORPS), which pumps 7 to 9 million gal per day (mgd) of raw sewage to the South Bay Water Reclamation Facility for water recovery, had a problem in its 50-by-10-by-30-ft wet well. A floating blanket of grease and debris, sometimes as thick as 4 ft, would occur on a regular basis.
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. As the city has had experience replacing its clogging non-clog pumps with Vaughan chopper pumps, it turned once again to Vaughan Co. for a more cost-effective solution.
The chopper pumps are ideal for use in pump stations and lift stations as conditioning pumps (patented with additional patents pending). When used as a conditioning pump, a submersible Vaughan chopper pump 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 not only chops and mixes the grease and debris that can accumulate as a floating layer, but also chops and re-suspends heavier debris that can accumulate on the wet well floor. This homogenization of the wet well contents prevents buildup of grease and debris in the wet well and helps to prevent clogging of the non-clog pumps typically used as dewatering pumps for these stations.
For ORPS, Vaughan Co. selected an 8-in. submersible chopper pump with a 25-hp 1,200-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 two and a half months of use.