Is denitrification in the AO process anaerobic?

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The AO process is known as the anaerobic-aerobic process; it should be understood that denitrification falls under the category of anaerobic processes. However, when reviewing materials on anaerobic processes, most of them mention hydrolysis-acidification and methanogens, etc., which are quite different from denitrification. Some colleagues who have worked at other companies with anaerobic-nitrification-denitrification processes have pointed out that our denitrification process does not fall under the category of anaerobic processes; it is rather an oxygen-deficient environment. Yet, in anaerobic biological treatment methods, the addition of substrates such as acetic acid and glucose is indeed mentioned. Since it is still denitrification, this is confusing – does the denitrification stage belong to the anaerobic category? Could the various issues discussed in anaerobic theory also occur in the denitrification stage? I now understand that denitrification occurs under anaerobic conditions, not anaerobiosis. I would like to clarify the question: does the effect of sulfates on anaerobic conditions, as discussed in books on anaerobics, occur during denitrification? For example, do sulfate-reducing bacteria use the added glucose as a substrate to produce sulfides? In my understanding, during the denitrification process, the dissolved oxygen level is low (currently 0–0.1 mg/L), which may lead to a reaction in which sulfate is reduced to sulfides. If such a reaction does occur, does denitrification take place first, or does sulfate reduction occur first?