Screening System Solves Grease and Solids Fouling Problem

July 27, 2006

The Yountville Wastewater Treatment Plant, located in scenic Napa Valley, Calif., used to have a not so scenic problem.

The facility, which handles .55 mgd of wastewater from domestic sources as well as a nearby Veterans home, was getting deluged with rags and other debris that spilled over into various areas of the wastewater treatment process causing frequent maintenance headaches. The debris constantly clogged the pumps and then had to be removed manually.

Of particular concern was the solid waste from the nearby Veterans home, which contained enormous quantities of cooking grease. Once the grease entered the waste stream, it congealed into large blocks that coated and clogged the lines, increasing down time and maintenance problems.

After examining the options with their consulting civil engineer, the facility personnel determined that a screening device would be the best solution to remove the solids. A Franklin Miller Spiralift Model SL fine screening system was selected for the job.

Reliable and effective

This screening system employs a shaftless auger screw and a fine perforated screen that captures debris. When this "screw screen" is combined with a Taskmaster Titan Grinder, the Spiralift system achieves its desired level of reliability and effectiveness.

First, the grinder reduces the solids to a small size and loosens up any trapped organics. A spray wash system then washes the helpful organics off the solids and back into the flow while reducing the odors of the screenings. The perforated screen is wiped by the auger brushes and conveyed up and out of the system. Next, the homogeneously ground solids are conveyed up the auger while free water flows back in. The resulting output is washed, homogeneous and easily disposed. In addition, the unit operates at a slow rotational speed, therefore consuming very little power. "We immediately saw the difference," said Don Moore, wastewater system supervisor. “The combination of Spiralift and grinder virtually eliminated the debris and most of the grease. In our application, it has helped us immensely." The system is easy to employ for a variety of channel sizes and capacity requirements. Three models are available for small, medium and high flows in narrow or wide channels. These units can be built to convey solids up a great distance.

A special control system integrates and coordinates the normal and special functions. The PLC based control system uses flow level data to cycle the screw to further minimize power and wear. The units can also be supplied with a bagging system to fully enclose the discharged solids, as well as a weather protection system that prevents freezing in exterior installations in cold climates.

"I was also impressed at how Franklin Miller has always been there when we needed them," said Moore. "Whenever we call them, they get right back to us. I'd definitely recommend the Spiralift System ."

About the Author

Sondra Sommer

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