TERTIARY NITRIFICATION IN AERATED PILOT BIOFILTERS

Three different types of internally aerated pilot scale biofilters wer e operated as tertiary nitrification systems. Long-term performance of the three aerated biofilters was tested under various operating condi tions. The maximum volumetric nitrification rates under non NH4-limiti ng conditions for the three aerated biofilter systems were investigate d. Based on measured temperature dependencies, an exponential relation ship was established enabling the prediction of the nitrification rate s at desired temperatures. Based on a temperature of 10 degrees C, the results allow a comparison between the surface and volume specific ni trification rates in the tested biofilters as a function of the NH4 ef fluent concentration. As shown by experiments, nitrification performan ce depends on water as well as air velocities in the filter. Higher ve locities of both air and water increase the nitrification rate. Howeve r, they also increase the head loss and thus decrease the filter run t ime. Therefore, the optimal operating conditions depend also on the fi lter media and the required effluent quality. Compared to fully O-2-li miting operating conditions, nitrification performance during a period under partially NH4-limiting conditions clearly decreased in all test ed biofilters.