wastewater
and robust solution called Membrane Bio Reactors (MBR), which is operated in ‘split’ configuration. Unlike wastewater applications ashore, black and grey water are kept separate on ships. This provides a unique opportunity to segregate, or to ‘split’, the treatment of black and grey water on the basis that the latter is far less contaminated and can be readily treated using existing MBR plants to a high standard, allowing it to meet all rules. Grey water accounts for 80 per cent or more of the total wastewater on a ship. Black water is also treated by an identical MBR plant that
results in it meeting all the Alaska criteria while the ship discharges as it is underway. The solution has proved to be extremely successful on multiple cruise ships over past Alaska seasons. Unique features include the use of existing AWT systems without increasing the footprint, energy, or skill requirement. The solution is future-proofing because it also allows simple
and robust compliant operation in the Baltic Sea. The nutrient- rich black water, once processed by existing AWT technologies, can be offloaded as a much smaller volume than would otherwise have been the case. This has two important benefits. Firstly, the nutrients in black water are then removed at very
high efficiency in mega-scale state-of-the-art municipal wastewater treatment works. This results in less nutrient load into the Baltic Sea than that which is intended by the legislation. Wastewater from Baltic-going cruise ships has an estimated 74t of nitrogen per year. This load could be reduced to 25t if black and grey water are mixed and then treated on board by nitrification and denitrification processes designed to comply with the 20 mg/l discharge limit. The ‘split’ configuration reduces this load to 4t, without having to have nitrification and denitrification processes on board. Secondly, this solution will make the 300 m3/hr port reception capacity insisted on by the cruise industry a more feasible long-term target without having to increase it further when considering the growing complements of newer ships, and wastewater held on board prior to a port call. Industry welcomes environmental regulations that are science- based, practicable and with tangible environmental benefits. Such rules need to be enforced to serve environmental needs. PST
Different solutions
There are a number of suppliers in the market offering black and grey water systems including Headworks, RWO and Rochem. Evac acquired Triton Water Maritime Solutions & Services of Germany in 2012 and now operates as Triton-Evac, providing MBR systems as well as other water treatment and generation products. Headhunter Inc supplies small ships such as the day cruiser Klondike Express, which operates in Alaska and expedition cruise operator Metropolitan Touring, with its Tidalwave HMX sewage treatment plant. These systems are able to process up to 50,000
gallons (187m3) per day and use flocculants, chemical oxidation, hydro-maceration and patented crossflow separation techniques to destroy influent biomass. The six-stage process provides trouble- free treatment of black and gray water and a sterile effluent for disposal. The PLC controller allows treatment techniques
to be customised after installation for varying hydraulic and organic loading conditions or to meet varying performance standards in different parts of the world, according to Headhunter. “All of our waste treatment systems are certified
for worldwide compliance under MARPOL,” said president Headhunter Inc Mark Mellinger. The current system received USCG and Bureau
Veritas approvals in 2010, according to MEPC 159(55). The basis of the treatment technology has been in operation since on PDVSA commercial vessels in Lake Maracaibo, Venezuela. Severn Trent De Nora’s Mariner Omnipure
system uses the company’s electrolytic disinfection technology to provide safe and effective treatment of black and grey water for up to 75 persons. The electrolytic process generates a powerful oxidant from seawater to disinfect the biological wastes, reducing their environmental impact. Unlike some sewage treatment technologies, no complicated or unsanitary pre-treatment of the raw inlet sewage stream is required. The electrolytic process also eliminates the need to purchase, store and handle hazardous chemicals required with other treatment technologies. The system is a compact, lightweight unit
that features a space-saving bulkhead-mounted arrangement – a first of its kind according to Severn Trent De Nora. It is an economical and simple treatment solution that integrates into existing piping systems because it utilises the vessel’s installed sewage and seawater pumps and in-place collection/holding tanks. The treatment system interfaces seamlessly via simple, low-voltage control circuits. The system has received the certificate of
Headhunter Tidalwave HMX sewage treatment plant uses a six-stage treatment process that can be customised
58 I Passenger Ship Technology I 2nd Quarter 2013
approval from the United States Coast Guard (USCG) in accordance with MEPC.159(55) effluent standards. It also has Bureau Veritas certification to MEPC.159(55) standards.
www.passengership.info
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