A Closed Ecological System (CES) is a broad term that encompass any self-sustaining and closed system in which matter does not leave or enter. These artificial habitats can be built in space, underground, or underwater, but no matter where they are, chances are they are closed for a reason. Whether it is an underground bunker in a post-apocalyptic setting, a distant planet in the early stages of colonization, or a spacecraft carrying the last remnants of humanity, the environment outside is not hospitable. To ensure long-term survival, the occupants must maintain a well-balanced air and water system, a continuous food supply, and a reliable source of energy.