Aerobic Reactor/Anoxic Reactor
Aerobic treatment of wastewater is a biological process that uses oxygen to break down organic contaminants and other pollutants like nitrogen and phosphorus. Oxygen is continuously mixed into the wastewater or sewage by a mechanical aeration device, such as an air blower or compressor. Aerobic microorganisms then feed on the wastewater’s organic matter, converting it into carbon dioxide and biomass which can be removed.
Aerobic treatment of wastewater is a stable, simple, and efficient process that produces high-quality secondary effluent. The resulting sludge is odour-free and can be sold as excellent agricultural fertiliser.
When combined with anaerobic treatment, aerobic treatment systems ensure complete contaminant and nutrient removal.
In an anoxic reactor/tank, denitrification takes place. Denitrification in wastewater treatment is the conversion of nitrate (NO3) to nitrogen gas (N2). It is a process that involves the reduction of nitrogen present in waste streams to an acceptable level so the treated water can be discharged into the environment via streams, ponds, lakes, etc.
Lowering nitrate levels in a waste stream is achieved through creating an anoxic environment in which heterotrophic bacteria use nitrate as an oxygen source to break down organic substances.
Heterotrophic bacteria obtain their oxygen through the following sequence: free and dissolved oxygen, nitrate, and then sulfate. When deprived of readily available oxygen, as in an anoxic environment, bacteria will use nitrate as an oxygen source to break down carbon, their source of food.
During denitrification, the tank is agitated but not aerated, thereby starving the bacteria of readily available oxygen. This forces the bacteria to break down the nitrate in the activated sludge to use as their primary oxygen source.
The breakdown of nitrate from the waste stream releases:
- Oxygen: which is consumed by the bacteria
- Nitrogen gas: which is released into the atmosphere
The goal of the denitrification process is to bring the waste stream within permitted nitrogen levels.