Control of intermittently aerated nitrogen removal plants by detection endpoints of nitrification and denitrification using respirometry only

A method is presented to detect the end-point of nitrification and denitrification in an intermittent aerated and intermittent fed activated sludge plant by means of one single respirometer. The method is based on the measurement of the respiration rate of activated sludge sampled from the reactor during the aerobic and anoxic phase with use of an intermediate aerator between the activated sludge sample point and the respiration vessel. The end-point of nitrification is detected as a sharp decrease of the respiration rate as soon as the concentration of ammonia reaches the ammonia half-saturation value. The end-point of denitrification is detected by a rapid and immediate increase in respiration rate. Increase of respiration occurred due to accumulation of readily biodegradable organic compounds which are not used anymore for denitrification. It is concluded that the proposed method detects both end-points of nitrification and denitrification in a reliable and fast way.