INTERACTION BETWEEN AERATOR TYPE AND SIMULTANEOUS NITRIFICATION AND DENITRIFICATION

Before the formal partitioning of bioreactors for nitrification and phosphorus removal, high levels of nitrogen removal were achieved in some channel systems – a phenomenon described as simultaneous nitrification and denitrification (SND). SND is common in channel type systems, and probably more common in extended aeration plants using point source aerators. In many plants, surface aeration equipment is being replaced with fine bubble systems for the perceived energy savings, but this perception may not always be valid when also considering the benefits of increased SND with surface aeration equipment. This paper reviews the theory of SND and how aeration equipment can have a profound effect on the degree of SND achieved through secondary treatment. Comparisons of plant performance comparisons are made in terms of the level of SND and the plant configuration and aeration systems used by the plants. Theoretical energy requirements for various aeration systems are also compared based on commonly used design criteria and the achievable level of SND for the aeration systems. Ideal surface aerator arrangements for optimal biological nutrient removal (BNR) are discussed based on several successful surface aerator installations.