Approach for a novel control strategy for simultaneous nitrification/denitrification in activated sludge reactors

Biological nitrogen removal in activated sludge processes is conventionally obtained by a sequence of aerobic and anoxic processes. Kinetic mechanisms affecting the oxygen balance could trigger the production of total volatile organic carbon (TVOC) and nitric oxides (NO) under anoxic and anaerobic conditions. Measurements at a wastewater treatment pilot plant of capacity 1.6 m3 wastewater show that the amount of TVOC and NO produced during the treatment process depends on carbon loading (low feed, balanced and overloaded) and aeration conditions. To confirm the results ORP, pH and dissolved oxygen (DO) are measured on-line and chemical parameters such as nitrate (NO3-N), ammonium (NH4-N) and TOC are measured in the wastewater. The ORP observed is in the range of −60 and +198 mV includes optimal setpoints for simultaneous nitrification and denitrification. From the pattern of NO emission plot, it can be assumed that a part of the produced NO3-N is denitrified during the aeration period. NO emissions are especially high during denitrification conditions at low oxygen rates. The results suggest that both NO and TVOC emission concentrations in combination with ORP can be valuable parameters to control operation of a wastewater treatment plant. Continuous measurements of ORP and NO concentrations for estimation of NO emissions gauging the extent of nitrification or denitrification in the plant becomes possible.