Some vessels are equipped with advanced water treatment plants, also called Advanced Wastewater Purification (AWP) systems, instead of traditional MSDs. They are most commonly found on ships that sail in Alaskan waters and sometimes work in parallel with an onboard MSD. Royal Caribbean International, for example, havsinstalled AWP systems on its ships which treat wastewater using advanced technology. Royal Caribbean AWP systems include three types of water purification systems: Scanship, Hydroxyl/Headworks and Navalis. Scanship and Hydroxyl use biological treatment while the Navalis system primarily uses advanced oxidation and filtration methods. Scanship and Hydroxyl systems use bacterial to consume the waste while also utilizing a chemical in order to break down and remove solids. Scanship and Hydroxyl systems are very similar to water treatment plants based on shore. This involves a simple five stage process. The first stage involves a prefilter where screens removes heavy and noticeable solids from the waste influent. Then the wastewater is passed through a biological reactor which uses beneficial bacteria to further break down any solids. Next the influent is pumped through a flotation unit which removes floatable waste. Afterwards, the clean water is passed through polishing filters which make the water even cleaner. The last and final stage involves an ultraviolet light reactor which disinfects the water. The final product may then be dried, incinerated, stored, or discharged at sea with respect to international regulations. The Navalis AWP system utilizes a seven-stage process to treat wastewater. The first stage involves wastewater entering the shaker screens which removes any noticeable solids. Then the wastewater is passed through an AET Roughing Reactor which help with chemical equalization and load. Then the influent is treated by a three-stage particle removal process which involve chemical flocculation, Hydraulic Separation, Tubular Filtration, and Ultra Filtration membranes. The waste influent is then passed through Oxidation Reactors which serve to oxidize pollutants and aid the production of carbon dioxide gas and water. The seventh and final stage consists of a powerful Ultraviolet Reactor in which the ozonated water is broken down into oxygen compounds that provide further treatment of the water. The leftover solids are then oxidized which provide safe bio-disposal or land based discharge if needed.