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Existing plant capacity at Plant No. 2 of Orange County Sanitation District (OCSD) is limited by sludge bulking, which in turn limits the solids and hydraulic loads that can be applied to the secondary clarifiers. To address this issue, Orange County Sanitation District (OCSD) conducted an aeration basin selector zone feasibility study to evaluate the potential performance improvements and associated costs of implementing anaerobic selectors at the Plant 2 HPO secondary treatment system. An evaluation of alternatives for improving the performance and efficiency of the high-purity oxygen (HPO) activated sludge secondary treatment system was completed. Subsequently, the plant operations staff has made operational changes which resulted in significant improvements in sludge settling quality. These operational changes places the plant at a unique position where low solids retention time (SRT) is used as the means for controlling sludge bulking without impacting the plant performance. INTRODUCTIONPlant No. 2 uses a high-purity oxygen (HPO), activated sludge system for secondary treatment. The plant is divided into two trains, the East Train and the West Train. Each train includes four aeration tanks and six secondary clarifiers. Each train also has a separate secondary sludge pump station. The aeration tanks in the West Train are currently in operation, and the secondary clarifiers in both trains are operating.

Custom WebGIS tools allow integration of the maintenance management system (MMS), engineering drawings and geographical information system (GIS) at the Vallejo Sanitation and Flood Control District. The WebGIS tools allow all staff (including O&M, engineering, and management) to access the District's databases and maps of its sanitary sewer system through ordinary Web browsers ( Figure 1). Ultimately, the WebGIS tools may be available to the public through the Internet and a kiosk located at the District's headquarters. In addition, the structures of the WebGIS tools have flexibility to integrate with other databases and maps used by the District and the City such as billing databases and potable water and storm drain system maps.WebGIS developers worked with the District to understand its "business" processes before development started (Figure 2). By integrating the existing processes, the custom WebGIS tools compliment existing practices without creating new work. The MMS is still run by the O&M staff, and the engineering department maintains records of improvements to the system. Now, however, the O&M and engineering staffs are working from a shared source of information that allows each of them to perform their functions more efficiently.The WebGIS tools also help the District comply with portions of the proposed CMOM requirements now. The tools provide maps and asset/condition databases required by CMOM. The GIS maps and databases can also be easily integrated into a hydraulic model of the District's system. Engineering staff can graphically identify areas subject to SSOs, frequent maintenance, and/or odor complaints so capital planning can be targeted to achieve superior results. WEF/CWEA Collection Systems 2002 Conference

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