Unfortunately, many server farms feed from hydroelectric power
Unfortunately, they already use another renewable source. That's not exactly unfortunate is it? Unfortunate might be if they prefer to burn kittens to get their power, not because it's better, just because they like it.
Unless they're also using the nearby water to cool things (heck, it's not really an unless) then piping that hydroelectricity into the rest of the grid and using the server heat to drive the biogas production would still be fully viable.
I'd not be surprised if that the end manure is better fertiliser than raw faeces too, for people that were concerned about it reducing supply of that.