Whole-Plant Simulations for Two Pure-Oxygen Activated Sludge Plants in San Francisco

This paper discusses the usage of settling column tests, full-scale stress tests, and whole-plant simulators as planning tools to assess the ultimate treatment plant capacity as well as impacts of process changes to effluent quality, process performance, side streams, and biosolids production rates. These planning tools are described in detail and the results of their implementation are presented for the two pure-oxygen activated sludge plants in San Francisco, California.

The City and County of San Francisco (City) has embarked on a thirty-year Master Plan to plot the future course of wastewater treatment in the City. This necessarily involves assessments of the future of the City’s two secondary treatment plants - Southeast Water Pollution Control Plant (SEP) and Oceanside Water Pollution Control Plant (OSP). One goal of the Master Plan is to assess the treatment capacities of these two plants. BioWin, a biological process simulator has been chosen to work side by side with the full-scale plant studies to achieve this goal. The work detailed in this memorandum is based on the Water Environment Research Foundation (WERF) document, “Protocols for Evaluating Secondary Clarifier Performance” (WERF, 2001).

Both SEP and OSP are pure oxygen activated sludge plants. OSP treats flow from the western side of the City and has a design secondary treatment capacity of 43 MGD, with room for primary treatment of an additional 22 MGD. SEP treats wastewater from the eastern side of the City, providing 100 MGD of primary treatment and 150 MGD of secondary treatment. At the time of this analysis, SEP, unlike OSP, had implemented anaerobic selectors, which has greatly aided in improving sludge settleablity. Features of both plants are listed in Table 1.

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