Physical Modeling Reveals Secrets, and Identifies Modifications to Improve Hydraulic Performance Hany Gerges (1) , Rob Williams (1) , William Yu (2) , Glenn Bielefelt (2) , Rich Gereg (2) , Alex McCorquodale (3) , and Ioannis Georgiou (3) (1) HDR Engineering Inc, Walnut Creek, CA (2) Sacramento Regional County Sanitation District, Elk Grove, CA (3) University of New Orleans, Lake Front, LA ABSTRACT A scaled physical model of the high purity oxygen process at the Sacramento Regional Wastewater Treatment Plant was used to evaluate the flow distribution problems and identify potential fixes. A comprehensive field testing program was implemented to collect data needed for calibrating and verifying the physical model. The calibrated physical model was then used to determine possible solutions to improve hydraulic distribution. Minor modifications such as installation of vanes and baffles were found effective in improving flow distribution among individual tanks under certain flow conditions. Major modification such as widening a mixed liquor channel was identified as a possible solution to improve the flow balance between the south and north sides of the oxidation tank facility and increase hydraulic capacity the treatment plant. Key Words: physical modeling, high purity oxygen, flow distribution. Background The Sacramento Regional Wastewater Treatment Plant (SRWTP) uses high purity oxygen for biological treatment. The oxidation tanks operate under a small positive pressure of 2-4 inches of water. The plant has twelve oxidation tanks with eight located on the south side of the return activated sludge channel and four on the north side. The tanks are nearly identical with the inflow regulated by fixed finger weirs with approximately the same crest elevations. The main difference in the finger weir arrangements is that the south finger weir chambers are surrounded and separated from the first stage of the oxidation tanks by a curtain wall partition that extends from the roof to below the water line; these partitions do not exist on the north finger weirs (see Figure 1). The curtain wall prevents pure oxygen from escaping from the tank. The most important hydraulic different between the north and the south is that the MLSS from the north must pass over a large hump in the West MLSS channel. 3304 WEFTEC®.06 Copyright 2006 Water Environment Foundation. All Rights Reserved ©