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filter and SBR. Nitrification is also required for a low food-to-microorganism ratio
(Box 5.2), and high mean cell residence time (Box 5.3).
The nitrification process generates acid that lowers the pH in the aeration tank
and can inhibit growth of nitrifying bacteria. Nitrification stops at a pH below 6.0.
The biological reduction of nitrate to nitrogen is called denitrification. The process is performed at dissolved oxygen concentration below 0.5 mg/l, ideally below
0.2 mg/l.
Nitrogen
gas
Organic
Matter
Ammonium
Nitrite and
Nitrate
Fig. 5.11 Simplified conceptual diagram of nitrification and denitrification
Box 5.2 Food to Microorganism Ratio
The term food-to-microorganism ratio is ratio of microbial food entering a
treatment system divided by the weight of the microorganisms in the treatment system.
Box 5.3 Mean Cell Residence Time
Mean cell residence time is the average time that a population of microorganism will reside in a treatment system.
5.2 Engineering Control
filter and SBR. Nitrification is also required for a low food-to-microorganism ratio
(Box 5.2), and high mean cell residence time (Box 5.3).
The nitrification process generates acid that lowers the pH in the aeration tank
and can inhibit growth of nitrifying bacteria. Nitrification stops at a pH below 6.0.
The biological reduction of nitrate to nitrogen is called denitrification. The process is performed at dissolved oxygen concentration below 0.5 mg/l, ideally below
0.2 mg/l.
Nitrogen
gas
Organic
Matter
Ammonium
Nitrite and
Nitrate
Fig. 5.11 Simplified conceptual diagram of nitrification and denitrification
Box 5.2 Food to Microorganism Ratio
The term food-to-microorganism ratio is ratio of microbial food entering a
treatment system divided by the weight of the microorganisms in the treatment system.
Box 5.3 Mean Cell Residence Time
Mean cell residence time is the average time that a population of microorganism will reside in a treatment system.
5.2 Engineering Control