The Recycling Plant is where some of the waste products go when they are used to power up the UAC. Also the waste products can be turned into useable resources. The only known entrances/exits is: The Monorail Station. The Recycling Plant also has airlocks that lead to the Mars Surface.
Sector 1 houses the goo ratation. Sector 1 also houses the Primary Pump Station to store that goo.
Sector 2 houses the steam ratation.