CONTROL OF INTERMITTENTLY AERATED NITROGEN REMOVAL PLANTS BY DETECTION END-POINTS OF NITRIFICATION AND DENITRIFICATION USING RESPIROMETRY ONLY

A method is presented to detect the end-point of nitrification and den itrification 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 sample d 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 s harp decrease of the respiration rate as soon as the concentration of ammonia reaches the ammonia half-saturation value. The end-point of de nitrification is detected by a rapid and immediate increase in respira tion rate. Increase of respiration occurred due to accumulation of rea dily biodegradable organic compounds which are nor used anymore for de nitrication. It is concluded that the proposed method detects both end -points of nitrification and denitrification in a reliable and fast wa y. (C) 1998 Elsevier Science Ltd. All rights reserved.