Anaerobic has no electron acceptors such as oxygen, nitrate, sulfate etc. Anoxic is the limitation of oxygen so that nitrate will become the electron acceptor during denitrification. - Javier is correct, oxygen is the electron acceptor, not donor as I previously had mentioned.
In the denitrification process, nitrate acts as a terminal electron acceptor. The electron donor for denitrification by heterotrophic facultative bacteria is organic matter
The main difference between anaerobic and anoxic processes is electron acceptor and donor. In anaerobic process, electron acceptor is also organic matter like electron donor. Sometimes sulfate also serves as alectron acceptor, which is undesired situation. In anoxic process, electron acceptor is nitrate and donor is organic in heterotrophic process. On the other hand, another DN process is being attractive, autotrophic denitrification; electron donor is H2 gas
The simple distinction between anaerobic and anoxic conditions in wastewater practice is that anearobic condition means there is no molecular oxygen and no oxidized nitrogen species (i.e, nitrite, nitrate, etc.) to use. Anoxic condition means there is no molecular oxygen but nitrite/nitrate is present. Type of electron donors does not have any impact on whether the environment is anaerobic or anoxic.
"Anoxia" (adjective: "anoxic") refers to the condition of an environment where there is no molecular oxygen (O2).
"Anaerobe" (adjective: "anaerobic") refers to the condition of an organism which is able to thrive without molecular oxygen (O2).
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It seems that there may be a confusion stemming from the ambiguity of the term "oxygen", which can refer both to the oxygen atom (O) and to the molecular oxygen (O2).
First, there is virtually no place on Earth with no oxygen atom (O), since water is made up of H2O, air contains 21% (by volume) of O2 (plus minor ammounts of CO2 and water vapor), and the crust contains 46.6% (by weight) of oxygen atom (O). Thus, I think it can be misleading to say that there are environments without any type of oxygen (neither bound or free) on Earth.
Second, terrestrial life is impossible without the oxygen atom (O), since it depends on water (H2O) and all four major classes of biomolecules have the oxygen atom (O) in their chemical composition (nucleic acids, carbohydrates, proteins, and lipids).
In contrast, there are many terrestrial enviroments depleted of molecular oxygen (O2), and there are many organisms that can thrive without molecular oxygen (O2). These organisms are called anaerobes, and the etymology of this word reveals its biolgoical origins: from the French word "anaérobie", coined by Pasteur in "Études sur la bière" (1863):
"On pourrait partager les êtres vivants en deux classes: les aérobies, c'est-à-dire ceux qui ne peuvent vivre sans air, et les anaérobies, qui, à la rigueur et pour un temps, peuvent s'en passer..."
Today, the adjective "anaerobic" is also used to the metabolic processes carried out by anaerobes, such as anaerobic respiration (in which the final electron acceptor is different from O2).
Therefore, one may say that anaerobes are able to carry out anaerobic respiration (or fermentation) under anoxic conditions.
http://www.cnrtl.fr/etymologie/ana%C3%A9robie
http://www.etymonline.com/index.php?term=anoxic
Thank you very much M. Vinicius Waldow for your answer.
B. regards
M. Ouhsaine Morocco
Great answers above. Just something additional:
Types of Microbial Metabolism
Aerobic microorganisms: When molecular oxygen is used as terminal electron acceptor in respiratory metabolism it is referred as aerobic respiration. The organisms that exist only when there is molecular oxygen supply are called as obligately aerobic.
Anoxic microorganisms: For some respiratory microorganisms oxidized inorganic compounds such as sulphate, nitrate and nitrite can function as electron acceptors in absence of molecular oxygen; these are called as anoxic microorganisms.
Obligately anaerobic: These are the microorganisms which generate energy by fermentation and can exist in absence of oxygen. They are only active in total absence of oxygen (free oxygen or bound oxygen)
Facultative anaerobes: These microorganisms have ability to grow in absence or presence of oxygen. These can be divided in two types:
(a) True facultative anaerobes: those can shift from fermentative to aerobic respiratory metabolism, depending on oxygen available or not;
(b) Aerotolerant anaerobes: these follow strictly fermentative metabolism and are insensitive if oxygen is present in the system.
Key Reference: NPTEL IIT Kharagpur Web Courses: Wastewater Treatment
the difference between anoxic and anaerobic condition is the type of electron accepter ,,in the anaerobis condition there is no melocular of oxygen and nitraite ,,in the anoxic condition the oxygen not exist but the nitriate used as electron accepter
Interesting answers. Both words basically mean oxygen-free. For the treatment of wastewater it is useful to distinguish between two oxygen-free treatment systems, the anaerobic tank where organic carbon is removed, and the anoxic tank where denitrification occurs. A lot of answers come to the conclusion that anaerobic means 'nitrate free' as well.
The confusion occurs when you describe microbes as 'anaerobic' or 'anoxic'. Anoxic microbes live in an oxygen-free environment, while anaerobic microbes respire on substrates other than oxygen. This means that denitrifying organisms are anaerobic microbes living in an anoxic environment.
Like the term 'fermentation', these words have different meanings depending on the specializations of the scientists who use them. Unless you are working in the wastewater field it is best to use 'Anoxic' to describe the environment, and 'Anaerobic' to describe the microbes metabolism.
Anoxic is used to describe environments without molecular oxygen. Anaerobic refers to microorganisms which are able to live without molecular oxygen. The metabolism they use is also called Anaerobic. So anoxic refers to environments and anaerobic refers to microorganisms and processes.