The secondary treatment system at the Yuba City, California Wastewater Treatment Facility is a high purity oxygen UNOX System. Yuba City was the first high purity oxygen wastewater facility in California. The system consists of 3 aeration trains, each train containing 4 stages. Each
stage is equipped with a surface aerator. Oxygen is supplied from a single 21 ton per day (TPD) pressure swing adsorption (PSA) oxygen generator. Current dry weather influent flows average 6.0 mgd. During the summer, when power costs and demand charges are high, the temperature of the influent
wastewater increases to approximately 29.4°C The only reliable way to handle the mass transfer requirements at these elevated temperatures has been to operate two UNOX System trains, even though hydraulically one train would be sufficient. In early 2002, Yuba City had fabricated 4 new
high efficiency surface aerator turbines under a special demonstration program agreement with the turbine's manufacturer. These turbines were then tested in the WTF's tanks using ASCE standard tap water test procedures. The testing indicated that these turbines, called the HI-FLO
Surface Aeration System, had approximately 17% higher mass transfer efficiencies than the units that were originally installed in the WTF. When retrofit on the WTF's existing, 25 year old gearboxes and shafts, the more efficient turbines increased the oxygen dissolution capacity
of this equipment sufficiently so that single train operation was possible during the summer of 2002. Once installed, the new aeration system reduced oxygen dissolution power consumption by 33%, from 205 Hp. to 137 Hp. with no detrimental effects on biological performance. Similar savings
may be available to wastewater facilities that have hydraulic capacity, but require increased oxygen dissolution capability.
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