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 a 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.
Mobile Dewatering Units: During the Summer of 2020, Tres Rios WRF needed to take down their entire centrifuge dewatering facility for contractors to install the second new Schwing Bioset Cake Pump. The pumping system details are explained in Pima County, AZ, Tres Rios WWTP Biosolids System Upgrades – Part One: Cake Pumping. Operations had to find a reliable solution to divert flow from the entire 30 MGD facility. Schwing Bioset again had an opportunity to help, providing our massive FSP1103 and FSP703 Screw Press dewatering trailers for temporary dewatering.
Thickened sludge was fed from the Anerobic Digester to both presses. Once the sludge feed was connected via cam-lock hoses, power connected to the trailer, and the drain lines hooked up, the Screw Presses were ready to run. Technicians dialed in the polymer dose, screw press floc tank pressure, screw rotation speed, and discharge cone pressure to optimize performance. The Tres Rios operations team could then to divert sludge flow to the temporary dewatering trailers, and each system is capable of the following throughput:
FSP1103 Trailer: Anaerobic Sludge
3208 dry lbs. / hour (1455 dry kg / hour) up to 214 gallons /minute (810 liters / minute) at 3% solids
FSP703 Trailer: Anaerobic Sludge
1365 dry lbs. / hour (620 dry kg / hour) up to 90 gallons /minute (340 liters / minute) at 3% solids
The FSP Screw Presses provided reliable dewatering for the entire Tres Rios facility for a few weeks while the new cake pump was installed. The presses were able to produce cake and filtrate quality performance near the plants existing centrifuges, producing an average of 17% cake solids while running near design capacity. The FSP screw press dewatering systems offered this level of high-performance dewatering and are a simple, easy to maintain, low energy consuming package, even at high flow rates from big plants.
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Read the previous Pima County Project stories and stay tuned for Part Four on Struvite Management:
Part One: Cake Pumping
Part Two: Live Bottom Bins
Part Four: NuReSys Struvite Management Project