I don't know what a force main is. So, answers below may not apply.
H2S can be oxidized but kinetics are slow, hours? Something like copper sulfate can be used. H2S will react to precipiate copper as copper sulfide which can been removed by conventional solid/liquid separation. H2S is...
The air being pulled into the system may be causing a local cool spot where average dewpoint conditions do not apply? The question is, what is the dewpoint of the mixture?
How accurately do you know the dew point of the process air? (mean and standard deviation)?
Robert Odle
No comments on the area of the two metals?
Copper is noble to aluminum and will be the cathode. Aluminum is the anode and will dissolve. If the aluminum area is large and the copper area is small, and/or the water is not very corrosive/conductive, and/or they are not in electric contact, you...