Mixing It Up

Pulsed hydraulic mixing system helps a New Jersey municipal authority manage grease in its largest pump station.
Mixing It Up
Bubbles formed by the Hydro-Pulse plate power liquid and sediment off the bottom of the wet well and force them upward. The vigorous mixing action keeps grease in suspension.

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The 1.5 mgd RCA Pump Station, located in a commercialized area of Deptford, N.J., always had grease problems, but they grew worse with the development of 40 food establishments and the Deptford Mall.

The Deptford Township Municipal Utilities Authority increased the pumping schedule from twice a year to quarterly, but that still wasn't often enough. Power cables rising and falling with the thickness of the grease cap weakened the cables' support system. When it failed under the weight of a 12-inch-thick cap, the cables fell into the wet well and were sucked into the immersed pumps, stopping all three of them.

The ensuing emergency, which required two weeks of bypass pumping and several thousand dollars to repair the damage, convinced the authority to look for a permanent solution. Assistant superintendent Mike Cusick found the PHI-300 mixing system from Pulsed Hydraulics on the Internet. After a demonstration of the technology, the authority ordered a unit with two bubble-forming plates. Within a week, the grease was gone.

Dealing with FOG

The pump station, built in the mid-1970s, was upgraded in 2010. "We went from a two-pump dry well system to three 200 hp submersible wet well pumps from KSB, each delivering 2,000 gpm at 140 feet total dynamic head," says Cusick.

Technicians cleaned the 15-foot-diameter well with a jetter vacuum truck on a Sterling chassis from Clean Earth/Safe Jet Vac. The grease returned within one to two months. Disposing of it at the Gloucester County Utilities Authority septage pretreatment facility cost $600 per load.

Operators tried controlling the grease odor with deodorizers and enzymes, but they were ineffective. "Nobody complained, but anyone driving past the pump station could smell it," says Cusick.

The authority sought to control grease at the source by educating food establishments about the problems. Some cooperated; others did not. "Newer buildings have grease interceptors," says Cusick. "Older ones have grease traps, but many aren't maintained. Until the authority completes its development of a grease ordinance, we have to deal with it."

Plate tonic

Carl Janson, president of Pulsed Hydraulics' distributor, Riordan Material Corp. in Blue Bell, Pa., demonstrated the mixing system with a Hydro-Pulse bubble-forming plate in the wet well. He plugged the Pulse Mixer control panel into an electrical outlet at the station.

"We brought a mobile air compressor and Carl hooked the air lines to it," says Cusick. "Installation was that fast and easy."

Janson weighted the stainless steel plate with 35 pounds, then lowered it 20 feet onto the grease blanket; however, the unit was not heavy enough to break through and sink to the bottom. "Carl turned on the system, and 100 psi bursts of air coming from underneath the plate gradually worked a hole in the blanket," says Cusick.

With the plate on the floor of the well, an electro-pneumatic valve with high-flow factor (Cv) that opens and closes in milliseconds released a massive, well-formed bubble every 30 seconds. The air burst powered liquid and sediment off the bottom, forcing them upward to smash into the grease. As the shock waves broke up the blanket, bubbles began breaking the surface, moving liquid and solids tangentially to the walls and down the sides to the bottom to complete the mixing cycle.

The Pulse Mixer with Allen-Bradley PanelView Plus 700 terminal (Rockwell Automation) controls the bubble-pulse intensity, duration and intervals. Its main components are the electro-pneumatic valve, a pressure regulator and 40 micron filter with auto-drain to control mixing air pressure (typically 50 psi), and a switch to set the mixing speed at low, medium or high based on the liquid's viscosity. Everything fits in an 18- by 16- by 8.5-inch NEMA 4X enclosure.

Dynamic duo

Initially, grease clogged the openings in the plate, but the longer the system ran, the more effectively it worked. "We cleaned the plates three times before the situation resolved itself," says Cusick. "It was an easy process."

The grease cap was too dense for the demonstration unit to remove it completely, so Cusick says the authority took a leap of faith and ordered a unit with two plates.

Before it arrived, the authority bought a QRS 5.0 (5 hp) 150 psi rotary air compressor from Chicago Pneumatic. An electrician hard-wired the power to the compressor and the wall of the pump station where the Pulse Mixer would be installed. Laborers ran two airlines underground and through a hole they drilled in the facing wet well wall. The work took two days.

Confident the bubble-forming plates would work their way through the grease blanket, the authority did not pump the wet well before installing the system. Janson programmed its operation.

"By the second day, we could see grease breaking up," says Cusick. "Within a week, most of it was in solution." The remaining deposits disappeared soon after and did not return.

The technology also reduced odors by 50 to 70 percent. "You have to be close to the wet well to catch any odor now," says Cusick. "It's no longer discernible from the road."

Based on saving $2,400 in annual disposal fees, the authority expects a return on investment in four to five years. After the system ran for four months, Janson returned to adjust the air pressure and mixing schedule to maintenance levels. "That will save us more money, but it is too early to say how much," says Cusick. "The system also has extended the service life of the pumps and decreased maintenance."

The authority plans to install single-mixing systems in other pump stations with grease problems.


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