i am in the sewage treatment industry

well maintain plant usually no smell, worst of u might smell abit during rainy days

the plant looks like a major plant, if nearby there is new development tapping into the existing plant, the upgraded plant will be fully enclosed. Just FYI

if properly maintained, smells usually does not occur as it has been fully digest by the bacterias in the pond

as for corrosive or not, yes and no

yes usually if it's enclosed plant and not properly maintain
also for enclosed plant, usually there will be a scrubber system to scrub the remaining gas out

no if its open air, i dont think its tht toxic since its already diluted with the air
having said so, i dont have the figures to prove my point, just based on experience

true, if u are close enough, u ll definitely able to smell it