Case Studies

Headworks and Biosolids

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Bar screen lowers maintenance costs


The Camrosa Water Reclamation Facility in Camarillo, Calif., recycles 1.5 mgd for irrigation, but the mechanical bar screen was not effectively separating debris from the wastewater before it entered the plant. Built-up debris blinded portions of the screen, bent rake fingers, and caused erroneous meter readings. Removing the debris required a confined-space entry and much manual labor. The unenclosed screen spread debris across the headworks, requiring more cleaning. The mess and smell attracted swarms of flies.

“Our biggest issue was the inability of the Parshall flume to record accurate levels,” says superintendent Robert Barone. “The flume measures and reports the flow to ensure that the district complies with its discharge permit. The debris caused the levels in the channel to fluctuate, creating errors in the flume’s accuracy. We had to replace that screen.”


The district chose the Mahr bar screen and Screwpactor from Headworks Inc. The front-raked, front-return bar screen handles 5 mgd. The rake bars have 3/16-inch openings mounted to chains on each side of the self-contained frame. The design eliminates solids carry over and is enclosed for odor control and improved hygiene. To eliminate erroneous flow readings, Headworks recessed the side frame and bottom of the screen into the channel walls and floor. “We now have the necessary headloss to secure accurate flume readings,” says Barone. The Screwpactor dewaters and compacts screenings to reduce volume.


Almost all the bar screen components are accessed at the top of the channel for fast, easy maintenance. “We save time and money because it operates effectively, and we no longer spend time cleaning debris scattered around the facility,” says Barone. “Even the flies are almost nonexistent. Although the equipment was not the least expensive solution, it was the most fiscally responsible in the long run.” 713/647-6667;

System prevents pump clogging, compacts trash


A San Diego (Calif.) pump station was filled with sheets, boots, strings, plastic bags and assorted trash. The pumps clogged often, causing manholes to overflow occasionally. Maintenance became excessive. Workers finally pinpointed the source of the problem when they found a book from the Richard J. Donovan Correctional Facility in the pump clog. The prisoners were using toilets as garbage cans.


The city considered installing a sewage grinder before the headworks screen, but operators worried about the high headloss across it. To avoid the expense of multiple grinders with a larger flow channel, or battling the overflow with pump clogging downstream, officials selected a combined grinder, bypass drum screen, and screw screen system from Pro-Equipment Inc.

The design integrates the Screen-Mate vertical drum bypass screen with a single grinder in the mounting frame to handle 2.4 mgd. As the grinder handles debris, the majority of the wastewater bypasses through the drum screen, reducing headloss across the system. The water and particles combine downstream before entering a Pro-Guard fine screw screen that filters, washes, and compacts the ground debris.


The system has operated since October 2010 without problems. An Allen-Bradley (Rockwell Automation) Contrologix PLC system monitors the components. When the Verbatim auto-dialer calls the operator, he identifies the problem on the Panelview touchscreen and troubleshoots it. 262/513-8801;

Anaerobic digester upgrade yields significant savings


The three anaerobic digesters at the Middletown (N.Y.) Wastewater Treatment Plant had no mixing or heating, which affected solids reduction and biogas production and increased operational and chemical expenses. As part of a plant upgrade from 6.0 to 8.5 mgd, the city turned to Infilco Degremont Inc. to modernize its solids facility.


Workers gutted the anaerobic digesters and installed Cannon Mixers from Degremont Technologies — anaerobic digester mixers with heating jackets. Vertical stack pipes, arranged to optimize mixing zones across the digester floor, keep solids in suspension with little settling. Large-piston bubble generation every three to four seconds per stack pipe ensures more than 90 percent total active volume in the tank.

The turbulent breaking action of the bubbles at the surface also prevents scum buildup. The heating jackets maintained the temperature at 95 degrees plus or minus 1 degree F to ensure high volatile solids reduction and biogas production. Workers covered the digesters to capture biogas, which the plant burns for process and facility heating. A new belt press was installed downstream of the digester to dewater stabilized sludge.


The anaerobic digesters are producing enough biogas to sustain process and facility heating, saving fossil fuel costs. The high volatile solids reduction has reduced labor hours, chemicals and solids hauling. The overall savings from the anaerobic digester upgrade is more than $140,000 annually. 804/756-7600;


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