The ecological balance of nitrogen Nitrogen can exist in variety of oxidation states from minus three in organic compounds to plus five in the nitrate form. For a schematic of the nitrogen cycle click here .
Raw sewage is rich in ammonia and organic nitrogen.
The biological conversion of organic nitrogen to ammonia is called ammonification. Since this process is rapid, our discussion begins with ammonia. When raw sewage enters a body of water, dissolved oxygen is lost first to the biological oxidation of organic carbon to carbon dioxide and then to the oxidation of ammonia. The uptake of oxygen in a body of water is expressed graphically as the classic DO sag curve. All waters have the ability to replenish a some or all of this oxygen through reaeration created by turbulence and to a lesser extent by aquatic plant life photosynthesis.