Sept. 23, 2003 -- A new rotary distributor with modulated speed control is eliminating the need for mechanical reducers and electric motors in a 170-ft. trickling filter at a South Salt Lake City, UT, wastewater treatment plant, saving the 75 mgd facility significant costs of maintenance, manpower and gear-drive replacement.
Called the HydroDoc™, the new design uses the hydraulic forces produced at the distributor arms to maintain a designated speed and flow application rate even when external forces such as wind or plugged orifices are applied. Very low rotational speeds of 4 to 60 min/rev allow plant operators to optimize the trickling filter process.
Moreover, when power is lost or air becomes unavailable, the distributor will continue to rotate at a preset default speed, and when normal conditions are restored, the distributor automatically resumes the programmed rotational speed.
"We experimented with this design when it was first developed and have now had it installed for more than a year with quite positive results," said Reed Fisher, general manager of Central Valley Water Reclamation Facility, which serves a population of 450,000 in this area's central valley region. The plant is designed for 75 mgd but operates at a daily average now of 50-55 mgd, Fisher said.
"The HydroDoc system is providing a very low maintenance operation with significantly less manpower required," Fisher said. "There's no need to change oil, no need for reducers and no risk of catastrophic failure. I estimate in the past year of operation we've saved at least $25,000 in electricity alone, and we haven't had to spend $10-15,000 each to replace gear drives destroyed by over-torquing."
The utility has ordered four more of the units for the plant's 170-ft. diameter, 14-ft. deep trickling filters.
Designed by WesTech Engineering of Salt Lake City, the HydroDoc system consists of flow control gate assemblies and positioners mounted on each arm of the rotary distributor, which control the flow through the orifice and spreaders mounted on the front and rear of each arm, which in turn propel the rotary distributor unit. It also includes a speed sensing assembly mounted at the top of the mast; and a panel mounted on the center assembly, which contains a control signal converter (this changes the PLC electrical signal into a pneumatic signal to operate the valve actuator positioners).
In the Central Valley Reclamation Facility installation, the system is connected to the plant's own PLC, and is programmed to slow down once a day to flush the filter.
According to Ralph Haymore, the system's inventor, the hydraulic-driven unit offers a myriad of advantages over traditional mechanically driven systems. Besides the obvious elimination of mechanical drive problems and maintenance required, the spreader ports covered by the gates are less apt to become blocked by debris, because the valve gates clean the ports at regular intervals.
Further, a preset distributor speed is maintained, allowing the arms to continue to rotate at lower flows without over-speeding at higher flows.
The system also utilizes an emergency-stop button that brings the arms to a stop without interrupting flow. This means operators can go to the center of the assembly in complete safety to check bearings, drain condensate, etc.
"There are thousands of trickling filters in the wastewater infrastructure today and many of them are idled due to lack of performance," said John Gottschall, sales manager for WesTech. "The HydroDoc can improve the performance of these existing trickling filters and, in turn, improve the performance of the plant itself without adding operational or maintenance costs to the municipality. "
WesTech® is an exhibitor at the WEFTEC® '03 event and can be found at Booth No. 3601