The rake arm mechanism inside the lime sludge gravity thickener tank at the Fort Pierce Utilities Authority (FPUA) water treatment plant (WTP) became inoperable and needed to be replaced. FPUA hired Globaltech under a continuing design-build services contract to replace the mechanism and implement several improvements to related equipment.

The project included design and construction of an emergency temporary dewatering/thickening system to continue the plant’s lime sludge thickening operation while the new rake arm was manufactured, delivered, and installed. The temporary system consisted of two 21,000-gallon rental weir tanks operated in parallel with gravity thickener influent lines running to the tanks and the discharge routed into the gravity system of the FPUA wastewater conveyance system. The sludge was pumped out of the bottom of the weir tanks using FPUA’s existing pumps.

Inside the gravity thickener tank, Globaltech removed the original rake arm mechanism and installed the new carbon steel mechanism, drive and motor; mounted a new control power panel to the new walkway-supported stanchions; and painted the new thickener mechanism with two coats of NSF epoxy. The existing walkway was extended and enlarged to accept the new drive.

Other work included installing two new centrifugal self-priming (trash) pumps with variable frequency drives (VFDs) on the thickened sludge pump station slab; replacing the wooden canopy over the slab with an aluminum canopy; modifying and/or replacing piping; and performing concrete crack and spall repairs on the gravity thickener.

Project Achievements / Benefits

• Designed, procured and installed an emergency dewatering system within 45 days
• Installed a sludge level detector inside the gravity thickener
• Installed multiple flushing connections to prevent solids from blocking lines