A Novel Method to Determine Blower Capacity of Wastewater Treatment Plants for Dry and Wet Weather Conditions

Ascertaining peak oxygen demand is crucial for plant designers to determine blower capacities of wastewater treatment plants in planning phase. To obtain this technical information without cumbersome influent sampling and analysis, a set of field-test activated sludge reactors equipped with DO and nitrate-N sensors was installed at 3 sites and continuously operated for a couple of months in each field. Under the controlled aeration and hydraulics of the reactors, the hourly influent oxygen demands were back-calculated as biodegradable constituents using the IWA-Activated Sludge Model #1. The daily maximum concentrations (rounded to last for 1-hour) of biodegradable organics and nitrogen were ranged between 45~258 mg-COD/L and 10.4~32.3 mg-N/L in Site #1; 119~244 mg-COD/L and 28.3~38.7 mg-N/L in Site #2; 194~552 mg-COD/L and 30.2~51.7 mg-N/L in Site #3 respectively. The marginal blower capacities to maintain at least 1.0 mg-O2/L of DO in the daily maximum oxygen demand were estimated based on the datasets using the statistical method, Extreme Value Distribution analysis. To maintain the DO concentration for 99 days out of 100 days of the plant operations, the blower capacity was supposed to be designed as high as 1.4~2.2 times than those of the blower calculated from the daily average concentration.