Threatened by a stench-driven lawsuit in 1995, the City of Rockport, Texas, took action to convert the last of its three dozen lift stations to submersible pumps. Now nearby residents and businesses in this Gulf Coast beach community can breath comfortably, and Rockports sewer system has seen a significant power cost savings.
Less than four years ago, Rockport faced serious problems with hydrogen sulfide at its Little Bay Shores pump station. The city fought the problem with chemical treatment, but odors lingered because of inherent design problems with the station.
"The solution was hardly a mystery," said Paul Guidry, a technician for the city. Unlike the rest of the systems lift stations, the Little Bay Shores station was equipped with a pair of self-priming pumps more than a dozen years old. The 25 hp pumps featured eddy-current, variable speed motors and were not very energy efficient.
The non-submersible pumps had to constantly maintain suction, making wet well clean-out far more difficult than for the rest of the Rockport system. The chemical treatment tended to float any solid particles to the surface in the lift station, forming a grayish, blanket-like mass on the surface. The dense sewage blanket could not be pumped and caused significant odors, Guidry said.
But the real crunch came from the difficulties in cleaning out the lift station. This routine required one of the staff to make every-other-day visits to the station for more than an hour to wash down the lift station and pump out the sludge blanket.
Submersing the Problem
Rockport was already using ITT Flygt submersible pumps at its other lift stations, where odor problems were minimal. When he was authorized to purchase new pumps for the Little Bay Shores lift station, Guidry decided to install similar units.
Submersing the Problem
"Flygt approached us and said they had a prototype of a pump theyd like to test, and that our South Texas coastal geography was precisely the setting they sought," Guidry said.
Submersing the Problem
As a result, earlier this year two ITT Flygt model 3127/NC-2 pumps replaced the self-priming predecessors. The new 10 hp pumps, with 6 inch volutes, currently handle 900-925 GPM at a 32 foot head.
Submersing the Problem
"After the installation of the two new Flygt pumps, we are now able to pump the wet well completely every day in just a matter of minutes, thus removing this blanket of floating solids that was causing the remaining odor problem," Guidry said. "Whereas we used to pump an average of 10 hours a day, we now average five to six hours. And during June in 1998, we saw our electric bill fall from the $245 per month that we averaged with the self primers, to $153 per month with the new Flygt pumps. With the cost of retro-fitting the station at about $20,000, our savings in electricity and manpower should pay for the remodel in about five years."
Submersing the Problem
The new units include a refined impeller design that - due to extremely close tolerances between the blades and volute - grinds and/or cuts up solids, allowing almost everything to pass through the pumps.
Submersing the Problem
While pump fouling was not a problem in Rockport, the new model has proven to be particularly helpful in other sewage or water treatment systems confronted by potentially snarling debris including masses of hair, rags, etc. The non-clogging function is effective against any kind of material that tends to string together, often causing "snakes" or "ropes."
Submersing the Problem
Rockport is a popular beach front town that swells with tourists on weekends and holidays. The sewer system is challenged by the wild swings in flow, and the flat terrain requires a huge number of lift stations. Submersible pumps have worked well in the system.
Submersing the Problem
"Submersibles require much less space above ground since everything, aside from the control panel, is below, and well out of sight. And, they really have impressive life spans," Guidry said. "We have a number of stations where Flygt pumps with 10 to 15 years of service and even 7,000 to 8,000 hours on them have never been pulled or worked on. And yet they are still in service."
