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Getting More “Bang for the Buck” on Wastewater Treatment Expansion Project

OC Watershed

After careful evaluation of the original expansion plan, several opportunities to enhance value and reduce capital and operational costs of the City of Somerton’s wastewater treatment plant (WWTP) were identified. When it came time to expand the treatment capacity of the City's municipal wastewater treatment plant, the City staff turned to their original design and expansion program for guidance. The original planned called for a 0.4 MGD expansion to provide a total capacity of 1.2 MGD, for a total cost of $6.2 million budget. However, PACE recognized an alternative approach that it proposed to the City that would expand the capacity by 1.0 MGD for the same budget, reduce land use and significantly reduce energy costs for operating the facility. Energy efficient turbine blowers were also added, reducing energy consumption by 15-20%.

Facility Expansion Overview
The Somerton Wastewater Treatment Plant (SWTP) Phase III Expansion increases the existing treatment capacity from 0.8 MGD to a total of 1.8 MGD. To increase the treatment capacity, the existing four-tank Sequential Batch Reactor (SBR) secondary process was converted into a four-stage continuous flow Biological Nutrient Removal (BNR) process.  For secondary clarification, two new clarifiers and a new RAS/WAS pump station were added. From the secondary clarifiers, treated effluent is disinfected, prior to gravity discharge to the Yuma Main Drain, through the existing chlorine contact tank. In addition, a new mechanical solids dewatering building was constructed to process bio-solids from the facility. No modifications were made to the existing influent lift station or headworks of the facility as these process units already have sufficient capacity to meet expansion needs. 

Each of the SBR tanks was converted to provide either Aerobic or Anoxic conditions within each in-service reactor.  The reactors are connected through a new mixed-liquor conveyance channel and a series of pumps and pipes which are valved to allow any number of reactors to be taken out of service while maintaining an operating process.  The valves also allow the completed facility to operate in several well-known activated sludge process modes, based on operator selection of configuration.  This provides ultimate flexibility with respect to current and potential future permit requirements.
Facility Expansion via Process Modification Yields Several Benefits:

  • Reduced land use by utilizing existing SBR basins as alternating anoxic and aerobic reactor tanks rather than constructing four new SBR tanks.
  • Expansion to 1.8 MGD achieved with 4-stage Continuous Flow BNR for the same budget of a 1.2 MGD expansion of SBR process.
  • Added 1.0 MGD of treatment capacity at under $7/gallon versus 0.4 MGD at over $15/gallon with an SBR expansion.

Reduced Energy Use Strategy
An evaluation comparing the energy costs of the existing Sutorbult rotary lobe blowers compared to high-speed single-stage turbine blowers (similar technology to jet engines) was performed to determine if a long-term cost savings could be yielded. Compared to the rotary lobe blowers with a capital cost of $55,000, the turbine blowers (K-Turbo USA Inc.) had a relatively high capital cost at $104,500. However, the turbine blowers operate with 15-20% less energy, with few moving parts, making maintenance easier and more cost effective. A payback period and 20-year lifecycle cost analysis was performed, demonstrating a significant cost savings from the turbine blower system.


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