EVALUATION OF BIOLOGICAL PHOSPHORUS REMOVAL IMPLEMENTATION ON WWTP PROCESSES USING A WHOLE PLANT SIMULATOR

Clean Water Services in Hillsboro, Oregon, wished to examine the effects of implementing biological phosphorus removal at their Rock Creek Advanced Waste Treatment Facility (AWTF). A whole plant simulator was used to examine the various options and the effects of the many operational variables on the processes.In order to use the simulator, it was necessary to first calibrate it. Calibration was accomplished in three levels: 1) gross plant configuration, 2) unit process performance, and 3) wastewater characterization. The wastewater characterization calibration (Level 3) effort did not fully match the plant data. After some investigation it was determined that this resulted from difficulties in sampling the raw sewage stream and possibly from inaccurate flowmeters used to measure the sludge stream flow. The partially calibrated model was still able to match much of the bulk operating data, however, and was deemed to be useful for modeling and prediction purposes.The modeling results showed that implementing biological phosphorus removal will require a higher solids inventory and thus either additional aeration or secondary clarification capacity. The amount of additional capacity needed was highly dependent on two primary plant operating parameters: the amount of volatile fatty acids in the influent wastewater and the amount of phosphorus that is inorganically removed in the digester system. Lower levels of volatile fatty acid reduced biological phosphorus removal efficiencies and thus required supplementation to achieve the needed phosphorus removal. Lower inorganic phosphorus removals in the digesters resulted in much higher levels of phosphorus being returned to the process, thus increasing the need for influent volatile fatty acids to meet equivalent phosphorus removals.The whole plant simulator was found to be very useful in predicting the effects of implementing biological phosphorus removal on the processes throughout the facility.