MONITORING OF NITROGEN REMOVAL PROCESSES BY USE OF CONDUCTIVITY MEASUREMENTS / Övervakning av kvävereduktionsprocesser med hjälp av konduktivitetsmätningar
A newly developed technology for nitrogen removal from ammonium-rich streams comprises two biological steps. In the first step, about half of the ammonium is oxidized to nitrite (partial nitritation) and in the second one, the remaining ammonium reacts with the formed nitrite into nitrogen gas (Anammox; anaerobic ammonium oxidation). The system was studied in a laboratory-scale pilot plant at the Royal Institute of Technology (KTH) and in a pilot plant located at the Himmerfjärden Wastewater Treatment Plant (WWTP). Both plants were supplied with ammonium-rich supernatant from digested sludge dewatering. Kaldnes rings were used as biofilm carriers. The process performance was closely monitored by analysis of different nitrogen fractions, COD, alkalinity and measurements of pH, oxygen concentration and temperature. Additionally, conductivity measurements were performed. It was found that conductivity is an excellent method to monitor the nitrogen removal processes. Such observation is based on the fact that the supernatant main salt is ammonium hydrogen carbonate, which further during the processes is converted to the carbon dioxide and nitrogen gas molecules. Theoretically calculated conductivity values were in good agreement with the experimental data. Conductivity turns out to be a reliable and Inexpensive method to evaluate different biological nitrogen removal processes used for separate treatment of supernatant.