Pima County, AZ, Tres Rios WRF Biosolids System Upgrades – Part Two: Live Bottom Cake Bins

Written by Josh DiValentino

Background: The district of Pima County, AZ, operates a total of eight wastewater treatment plants. The Tres Rios Water Reclamation Facility (WRF) is the centralized biosolids processing facility for all Pima County plants. Tres Rios WRF currently operates 24/7/365 at a 30 MGD capacity, with a projected flow of 50 MGD in 2030. The facility process is; BNR, Anaerobic Digestion, Dewatering, Pumping, Truck Loading, and Land Application of biosolids (cotton is common use). For nearly 20 years, Schwing Bioset, Inc. has provided solids handling solutions at Tres Rios with projects ranging from biosolids cake pumping and cake storage bins, to most recently, nutrient recovery and temporary Screw Press dewatering equipment.

Live Bottom Cake Storage: In 2012, the facility completed a Regional Optimization Master Plan expansion, which included upgrades to the centrifuge building and a new truck loading building. Prior to this expansion, dewatered cake was pumped (using the original Schwing Bioset Piston Pump) directly through a pipeline to the truck loading area. There was no intermediate storage capacity in the system on the dewatered cake side. Further, trucks could only be filled as fast as the cake pump could deliver cake, significantly reducing truck fill times.

Tres Rios Storage w-caption 2During the 2012 expansion, Schwing Bioset, Inc., supplied the new truck loading cake bins. Three (3) live bottom bins were provided, each with a capacity of 3,000 cubic feet of cake storage.

  • Bin Silo Sizing Details (each): Circular Design, 12’ diameter and 33’ tall storage area. Total height of 51’ including truck loading area.

Each bin utilizes a live bottom to deliver biosolids cake to the trucks below. The live bottoms are center discharging.

  • Bin Live Bottom Details (each): 18” diameter shafted, Twin Screws. Complete with 36” x 36” pneumatically actuated slide gates to control cake fill.

The top of the bins extend through the roof of the truck loading building. The bins provide storage capacity for dewatered cake and can fill trucks in less than 15 minutes when needed. The systems came complete with access ladders, safety railing, and ventilation connections for odor control. The bins have been in operation for nearly a decade, requiring only regular upkeep and maintenance to bearings and drive systems.

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Read Part One: Cake Pumping

Stay Tuned for More on Pima County Projects:

Part Three: Temporary Screw Press Dewatering

Part Four: NuReSys Struvite Management Project


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