TABLE 231 Genera of Bacteria That Include Denitrifying Species

Acetobacter

Achromobacter

Acinetobacter

Agrobacterium

Alcaligenes

Arthrobacter

Axotobacter

Bacillus

Chromobacterium

Corynebacterium

Denitrobacillus

Enterobacter

Escherichia

Flavobacterium

Halobacterium

Hyphomicrobium

Kingella

Methanonas

Moraxella

Neisseria

Paracoccus

Propionicbacterium

Pseudomonas

Rhizobium

Rhodopseudomonas

Spirillum

Thiobacillus

Xanthomonas nitrite respiration. The reduction of nitrate ions to only nitrite ions during denitrification may result in an accumulation of nitrite ions. This form of respiration in a secondary clarifier may result in the production of the ''chlorine sponge.''

Some genera of denitrifying bacteria are microaerophillic and can tolerate only low levels of free molecular oxygen. Some genera of denitrifying bacteria including species of Corynebacterium and Pseudomonas do not denitrify completely and produce nitrous oxide instead of molecular nitrogen as their gaseous end product.

Most denitrifying bacteria cannot ferment, that is, use a molecule of cBOD to degrade another molecule of cBOD. However, some species of Bacillus and Chromobacterium can denitrify and ferment at the same time. Finally, species of Propionicbacterium that denitrify cannot respire aerobically, that is, cannot use free molecular oxygen.

The enzymatic machinery needed for denitrification is formed only under an anoxic condition or the presence of a low oxygen concentration. However, the production of the enzymatic machinery for de-nitrification is accomplished quickly.

Denitrifying bacteria are common soil and water organisms and are associated with fecal waste. Denitrifying bacteria enter an activated sludge process through I/I and domestic wastewater. Many denitrifying bacteria are floc-forming organisms or are easily adsorbed to floc particles. Most denitrifying bacteria reproduce every 15 to 30 minutes and are present in an activated sludge process in millions per milliliter of bulk solution and billions per gram of MLVSS.

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