Anaerobic respiration / anaerobic

What happens in anaerobic respiration? Definition:

In the anaerobic respiration these are the inner respiratory processes of organisms that can use their energy metabolism completely without oxygen. On the chemical level, a redox reaction takes place. Instead of oxygen (O2However, nitrates, sulfates or fumarates (and some others) serve as electron acceptors.
Organisms with anaerobic respiration are called anaerobes (Greek 'an' = not, 'aer' = air), those who rely on oxygen are aerobes. There are two types of anaerobes:
obligate anaerobes: It is imperative to use an oxygen-free environment to survive.
optional anaerobes: do not need oxygen for their metabolism. However, an oxygen-rich environment does not harm them either.
Restoration, by the way, does not belong to the anaerobic processes. Although the fermentation process proceeds without oxygen, no foreign electron acceptors are involved.