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F BioRtration Process nitrifiers (nitrosonomas) will use the ammonia nitrogen and convert it to nitrite, then the second group of nitrifiers (nitrobacter) will use the nitrite and convert it to.nitrate. Nitrification is the second stage of treatment and BOD removal is the first A. stage. In a practical sense, if the facility converts 99 % of the ammonia to nitrate then one can assume BOD has been removed. De-nitrification is a step that occurs after nitrification and is the process of removing nitrogen from wastewater. It works by reversing the nitrification Process. This is achieved by manipulating the dissolved oxygen level. Total nitrification requires dissolved oxygen levels above 1.0 mg/l. To reverse this process, the dissolved oxygen level is lowered to or near zero. At this point, the oxygen will be stripped off the nitrate molecule by the bacteria and will leave only nitrogen atoms in the water. Nitrogen atoms will bond to themselves creating N2 which is nitrogen gas. Gas is lighter than air so it will escape from the water into the air (air is 80% nitrogen) as shown in Figure 2. ' Figure 2 Nitrogen gas Ammonia Nitrite Nitrate Nitrification Denitrification ....... Aerobic Digester Operation The digestion process reduces solids by starving the sludge until it dies. Sludge has three growth phases, the last phase Endogenous Respiration, takes place in the digester. It works by pumping WAS into the digester then providing the WAS with nothing but air. Sludge in the digester begins to utilize the food stored inside the cell wall. In addition, some organisms will consume other organisms. Overall, sludge feeds on itself. Envision a person on a strict diet getting energy from stored 7H Technical Services Group Operation &Maintenance Manual BioFiltration Process Page 10 of 26