Full-scale Test and Simulation of Simultaneous Nitrification and Denitrification

The objective of this research was to confirm the presence of simultaneous nitrification and denitrification (SND) in an oxidation ditch wastewater treatment process and to compare the operating characteristics of continuous aeration at low dissolved oxygen (DO) with cyclic aeration as a means for nitrogen removal. SND was confirmed by comparing the effluent concentration of oxidized nitrogen species in field tests to the predicted level in simulations in which denitrification had been suppressed. Simulations were used to compare the operating characteristics of different control strategies. The simulations indicated that a cyclic aeration control strategy resulted in less power consumption than continuous operation with low DO concentration and had approximately the same amount of denitrification, although nitrification was less complete. Operation at low DO did not result in a pronounced shift of filament populations to low-DO forms, although a weak correlation of increasing DO to improved settleability was observed..