Designing a Anoxic DeNitrification Mixing System:
Anoxic denitrification is an ecologically important bacterial process that converts reactive nitrogen compounds to inert nitrogen gas. The discharge of excessive amounts of nitrogen can result in the growth of large amounts of algae and a zone of low dissolved oxygen (hypoxia), which can stress aquatic life in receiving waters such as streams, lakes, bays, estuaries, etc. The primary method of denitrification is to introduce nitrogen-eating bacteria into the wastewater. Another method is to introduce a neutrally buoyant media to which the bacteria anchors itself while consuming the nitrogen.
Generically, bacteria uses the organic carbon found in waste water as its energy source. Through bacterial action, faculative bacteria reduce nitrates into nitrites which then evolves into nitrogen gas which can be properly vented to the environment as an inert (non-reactive) gas. The process is generally a closed system in that the mixing system is designed to minimize oxygen absorption from the atmosphere. Top entering mixers are used to maintain the activated sludge, which encourages the right biological communities to form resulting in an anoxic condition suitable for denitrification.