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Aerobic denitrification, conducted by aerobic denitrifiers, may offer the potential to eliminate the need for separate tanks and reduce sludge yield. There are less stringent alkalinity requirements because alkalinity generated during denitrification can partly compensate for the alkalinity consumption in nitrification.
Another important environmental issue concerning denitrification is the fact that the process tends to produce large amounts of by-products. Examples of by-products are nitric oxide (NO) and nitrous oxide (N 2 O). NO is an ozone depleting species and N 2 O is a potent greenhouse gas which can contribute to global warming. [3]
Recent results, however, show that HAO does not produce nitrite as a direct product of catalysis. This enzyme instead produces nitric oxide and three electrons. Nitric oxide can then be oxidized by other enzymes (or oxygen) to nitrite. In this paradigm, the electron balance for overall metabolism needs to be reconsidered. [7]
Nitrous-oxide reductase is a homodimer that is located in the bacterial periplasm. X-ray structures of the enzymes from Pseudomonas nautica and Paracoccus denitrificans have revealed that each subunit (MW=65 kDa) is organized into two domains. [ 7 ]
Approximately 78% of Earth's atmosphere is N gas (N 2), which is an inert compound and biologically unavailable to most organisms.In order to be utilized in most biological processes, N 2 must be converted to reactive nitrogen (Nr), which includes inorganic reduced forms (NH 3 and NH 4 +), inorganic oxidized forms (NO, NO 2, HNO 3, N 2 O, and NO 3 −), and organic compounds (urea, amines, and ...
Sewage treatment plants mix these organisms as activated sludge or circulate water past organisms living on trickling filters or rotating biological contactors. [5] Aquatic vegetation may provide similar surface habitat for purifying bacteria, protozoa, and rotifers in a pond or marsh setting; although water circulation is often less effective.
The use of nitrites in food preservation is highly controversial [22] due to the potential for the formation of nitroso-compounds such as nitrosamines, N-nitrosamides and nitrosyl-heme. [citation needed] When the meat is cooked at high temperatures, nitrite-cured meat products can also lead to the formation of nitrosamines.
A second hydrogen bond forms from Histidine or a nearby water molecule and leads to the cleavage of the N-O bond. The Cu is now five coordinate bonded to nitric oxide and water. Nitric oxide is released as Cu is oxidized to state (II) and returns to the resting configuration. [8]