There's a lot happening here. Worst of all, I don't know where exactly the question belongs. Lets see if we can get somewhere taking the questions point by point.
In normal condition, corrosion occur with the presence of oxygen, however there is a special case that often occur in our daily life which is corrosion in the absence of oxygen.
4Fe + SO42- + H+ + 3H2O --> FeS + 3 Fe(OH)2 + OH-
Water and metal is the main factor of corrosion to occur.
Corrosion occur with the presence of FeS
OK, that's clear. Note that there are many corrosion processes that don't require atmospheric oxygen, even if they're called 'oxidation'. So lets be sure we keep this in mind at all times.
Thing is, I don't really understand your reaction. Its possible, but may not be common, or plausible. Also, how is it describing what you're talking about? Your reaction describes an iron tank, full of sulfate ion and acid, reacting with water to produce iron hydroxide and hydroxide anion?
That just doesn't seem likely. I know dilute sulfuric can't dissolve iron like it can for a more active metal, but hydroxide forming? No, I don't see that happening.
In another study says the oxygen acts as the terminal electron acceptor for corrosion to occur by sulphate reducing bacteria in a mixed aerobic/anaerobic system.
Sure. But that likely works by a different mechanism than the one you've written above.
Is the above statement means if the inside of the tank (anaerobic condition) has corrosion occur, will it induce the corrosion of outside of the tank (aerobic condition)?
I suppose it depends on the thickness of the tank, but for anything thinker than a capacitor, no that doesn't seem likely.
Sulfate reducing bacteria is commonly known to bring the corrosion to occur. This bacteria is presence in neutral pH 7 which then reduce the pH and thus making the environment more susceptible to corrode.
Well, it'd be best if we had the reaction written out. Is that the one at the top? You should include the bacteria as a "reactant" or maybe as a catalyst to be clear. I'll go look up sulfate reducing bacteria, so that we're all on the same page. Someone in the biochemistry sub-forum may be able to help more.
Any method to prevent this bacteria to corrode from inside of the tank?
Appreciate for any idea.
Yes. An antibacterial that's compatible with your process will prevent them from surviving to perform the metabolism that may be corroding your tank. I have to assume this is not for food or medicine, so you can use anything: phenol or other powerful organic sterilizer, high temperature steam injection, heck, even short uv or gamma irradiation, if you have the money. Maybe someone in Chemical Engineering sub-forum faces this sort of problem.