A Change in Control Strategy Reduces Power Consumption at Colorado Springs Utilities

The JD Phillips wastewater plant at Colorado Springs Utilities commenced operations in 2008. Designed for the treatment of 20 MGD the actual flow is 8 MGD. The secondary treatment has three passes. The A pass is used for phosphorus removal and partial denitrification. Passes B & C are used for nitrification. The plant wants to insure compliance to its varying discharge permit while reducing costs.Due to high ammonia influent concentration and a deficiency in BOD it was soon apparent that the plant needed improvements: low alkalinity created some pH excursions outside the discharge permit. Also, energy usage was high. In 2009, a source for additional carbon was found and instruments to measure ammonium, nitrate and pH were installed.Multiple phases have already been implemented and further improvements remain possible. A step by step approach changed the way aeration and denitrification are controlled.In the initial phase the measurement of Dissolved Oxygen was used to control the aeration of the B and C passes. The set points were 2.5 mg/l in pass B and 1.8 mg/l in pass C.In a second phase presented at WEFTEC 2010 the DO set point in the B and C passes were driven by the concentration of ammonia. Savings in energy and chemicals related to the addition of whey, partial denitrification and the use of ammonia measurement were reported.In the phase reported now, the B pass air flow is now controlled directly based on ammonia. The internal recirculation is driven by the nitrate concentration in the C pass. The air flow to the C pass is controlled to maintain a minimum dissolved oxygen concentration at the end of the effluent channelAs a result of those changes in control, additional energy savings have been achieved. Close to 20% savings normalized for flow and ammonia load