The purification plant is a location seen in Season 9 of AMC's The Walking Dead. It is the home and base of operations of the Highwaymen before they merged with the rest of the Coalition.
Pre-Apocalypse
This was a purification plant before the apocalypse.
Post-Apocalypse
Season 9
"Chokepoint"
Elsewhere, Jerry, and Carol scope out the Highwaymen community while Ezekiel laments the violence they have to resort to. Carol suggests they try talking to them first, and if that doesn't work, then they'll kill them.
Ezekiel, Carol, and Jerry infiltrate the Highwaymen base, where the leader Ozzy informs them that the meeting is for the King alone. They disagree, sticking by Ezekiel's side. Ozzy asks if they have his toll, while his people approach with their guns and melee weapons drawn. He suggests they use Ezekiel as ransom, when suddenly the Kingdom fighters grab Ozzy's people from behind. Ezekiel draws his sword and says he's prepared to fight for what they've created. He then offers the man a job to clear the roads for him in exchange to access for the Kingdom and the fair. Ozzy laughs in his face and draws Jerry's sword, telling them they'll have to do better than that. Carol then asks when the last time they've seen a movie and a shocked Ozzy responds, "Seriously?"