NON-INVASIVE MONITORING FOR EARLY WARNING NITRIFICATION FAILURE

Work at full-scale wastewater treatment plants was carried out in order to establish whether N2O could be used to predict nitrification failure. Previous research on a pilot-scale activated sludge plant had shown a strong correlation between the increased N2O concentration monitored in the aeration tank, and the appearance of NH3 in the effluent, giving rise to the possibility that N2O could be used as an indicator for nitrification failure. N2O emissions were continuously monitored at two full-scale wastewater treatment plants, one municipal works and one industrial works. An activated sludge lane was continuously monitored at the municipal works. The results showed N2O concentrations of 7.2 ppm immediately after the anoxic zone, followed by a decrease in the N2O off-gas to background emissions ranging 0 − 2.1 ppm. The industrial works used a two-stage process for nitrogen removal, with both processes (stage one aeration tank and stage two aeration tank) and an anoxic tank continuously monitored. Stage one showed high peaks of off-gas N2O and NOx with background emissions ranging 0 − 80 ppm for N2O. Stage two had small spikes of N2O and NOx with background emissions ranging 0 − 20 ppm. High amounts of N2O were found in the denitrification tank with background emissions ranging 0 − 80 ppm. The results showed that the municipal plant had potential for using N2O to predict nitrification failure, where as the industrial plant with higher and more variable N2O release was more problematic.