Upgrading of wastewater treatment plants for nitrogen removal: Industrial application of an automated aeration management based on ORP evolution analysis

Upgrading conventional wastewater treatment plants for nitrogen removal involves total control of nitrification, denitrification and carbon removal. On low-load activated sludge processes, a comprehensive survey on fast and low kinetic biological reactions has been carried out, which describes the short-term and long-term requirements on the aeration sequences in a single tank. Although soluble and adsorbed pollution have to be treated in routine conditions, soluble pollution treatment becomes a priority during limited overloads, indicated by a slow ORP evolution. The treatment of adsorbed material is hence delayed. In order to implement the appropriate strategy, an automated aeration management system has been developed. This system is based on the analysis of both the real time signal and time evolution of the Redox potential signal. This information is used for command and control purposes. The application of this logic-based approach at full scale has been fruitful in evaluating its adaptability to the industrial environment and its potential results. The operation of seven plants under the control of the automated management system has enabled the nitrogen removal performance to be increased. Most of the nitrification and denitrification yields reach 90%, whereas previous results were far lower and more erratic. In addition, the present work determines limiting conditions for a guaranteed long-term result and a successful upgrading. (C) 1998 IAWQ. Published by Elsevier Science Ltd.