They might as well go the next logical step.
Growing lettuce requires soil and fertilizer.
They should integrated producing soil and fertilizer in to the building design.
All of the human feces produced by the people in the building should be collected and composted for use in their lettuce beds.
It may put people off eating the lettuce. But if you are going to push stupid ideas you might as well push it off a cliff.
Hehe, regenerative farming!