Demonstration of Intermitttent On/Off Aeration at a Municipal Wastewater Treatment Plant for Denitrification and Energy Savings

Final Report

Intermittent On/Off Aeration Determination of Denitrification Rate

Wastewater characteristics indicated that the effluent NO₃- concentration was around 25 mg-N/L, which was carried all over the oxidation ditches. A laboratory-scale experiment was conducted to pre-determine the denitrification capacity of Ashland activated sludge. The activated sludge (mixed liquor) were spiked with sodium nitrate (NaNO₃) as nitrate source and the denitrification rate was determined by measuring nitrate concentration. From Figure 3.1, the denitrification rate of Ashland activated sludge was estimated to be:

(40.2 - 26.6 mg NO₂-+NO₃--N /L) / 5 hours / 2260 mg/L = 1.2 x 10-3 mg/mg/hour,

where the initial biomass (MLVSS) in the batch reactor = 2260 mg/L.

Theoretically, it needed about 9 hours {25/[(40.2 - 26.6)/5]} to denitrify 25 mg/L of nitrite in ditches, based on the measured denitrification rate. Therefore, the jet aerators were shut off for 5 hours each day from October 16, 1995 to March 6, 1996 and 6 hours from March 6, 1996 to October 8, 1997 and 8 hours from October 9, 1997 to the present. A typical shut-off period was from 8:00am to 4:00pm every day. The shut-off period was adjusted in the full-scale demonstration study in order to achieve complete denitrification.

More information on this topic: Gerry Novotny