Managing and reducing waste aboard the Royal Navy’s new 65,000 tonne aircraft carrier HMS Queen Elizabeth is a complex task considering her size and the number of personnel she will be carrying.
In charge of the process is the Integrated Waste Management System (IWMS) which has been put to the test during the carrier’s sea trials.
The Aircraft Carrier Alliance, responsible for delivering the Royal Navy’s two QE-class carriers, explains the process:
The system ensures the proper and sanitary processing, storage and destruction of all waste types throughout the lifetime of the ship. This includes greasy grey water from the galleys and sculleries, bilge and sullage waste from machinery spillages and engineering activities and Black Water throughout the ship.
The bilge and sullage collection system itself has the capacity to hold up to 83 m2. The waste fluid is moved by one of the systems’ pumps where it is then stored before processing via the two oily water separators. Any water with an oil content below five parts per million is discharged overboard (International Marine Organisation standards are 15 parts per million). Any oil left over is then used as fuel for the Pyrolysis plant or stored before it is pumped ashore for proper disposal.
Greasy grey water from the galleys and sculleries is collected and processed through one of the four on board separators. Due to the relative densities of different grease types, they will naturally separate in the tank and will drain through valves at different heights in the separator. Pressurising the system allows both greases and excess materials to be forced into collection drums for disposal later.
Black water is transported from each of the ships 302 toilets via a vacuum system. The ‘waste’ is transported at nine metres per second through the pipe work to one of the three Membrane Bio Reactors (MBRs) which are capable of processing over one and a half times the expected volume of waste. Once processed, it is perfectly safe to drink, although it may not taste great!
Any leftover waste following separation and storage eventually finds its way to the Solid Waste and Final Treatment system where it is destroyed by Pyrolysis; a process which breaks down the molecular structure of the matter by exposing it to temperatures in excess of 800 degrees. This will usually incorporate a mixture of food waste, bio-sludge, dry solids and waste oil and medical waste. On completion the leftover product known as Char is stored within drums on pallets ready to be disposed of ashore.
In addition, to further reduce the amount of non-recyclable waste, the ship is fitted with Glass Processing Equipment which crushes and compacts leftover glass products for subsequent recycling.