A bio-matter resequencer was a device which recycled waste products aboard 22nd century starships such as the Enterprise NX. In this process, waste matter is sterilized and broken down for reuse in manufacturing boots, storage containers, and other necessities.
When the four Ferengi Ulis, Krem, Muk, and Grish took over the control of Enterprise and made the crew unconscious they tried to find the vault of the ship. Commander Tucker, who remained conscious, placed a security lock at the the entrance to the bio-matter resequencer room and presented this room as the vault of the ship. The Ferengi ran into a trap and were shot by T'Pol, who had been waiting behind the door. (ENT: "Acquisition")
In 2151, Enterprise captain Jonathan Archer delegated Molly McCook's question, "When you flush the toilet, where does it go?", to chief engineer Trip Tucker. Displeased, Commander Tucker protested having to answer the "poop question", but ultimately relented and explained the ship's processes of recycling and bio-matter resequencing. (ENT: "Breaking the Ice")