When you web-search an answer for how airliners maintain cabin air breathability, the typical answer you get is that bleed air is the key: new air comes in from the outside and gets mixed with old air.
But these days, some airliners are bleedless, such as Boeing's 787.
So, what maintains air breathability/quality in the cabin? Do they use oxygen tanks and some kind of CO₂ capture mechanism? What about other kinds of air treatment, e.g. for other gases, organic material etc?