Clear Waters Run Deep

Cruise lines industry-wide are undertaking waste management programmes to reduce the negative effects of its impact on the environment.

One major area of focus lies in controlling the wastewater that ships emit when operating at sea with the installation of technologically advanced wastewater purification (AWP) systems. At the end of the cleaning process, the wastewater is so clean that it exceeds all existing standards for water that is discharged from ships. In 2006, Celebrity Cruises installed AWP systems across its fleet and will continue to do so throughout 2007.

INVESTMENT FOR SUSTAINABILITY

Celebrity’s commitment to advanced wastewater purification systems is an example of its policy of continual environmental improvement. Over the next few years, each of its ships will be equipped with an AWP system, representing a total investment of over $50m. Installation of the new systems will begin either when a ship goes into its normal scheduled dry dock or, in some cases, while the ship is in service.

Typically, it takes four to five months to fabricate a system in the factories and four months to install one on board. Commissioning the system takes a further two months and includes a sampling period to ensure the system’s performance meets standards comparable with those set by the State of Alaska, regardless of where the ship is operating. All new Celebrity ships will have one of five AWP systems installed.

ZENON

The Zenon system uses a coarse mechanical screen to remove wastewater solids, such as plastics, before they enter the treatment process. An important part of the system is a biological reactor, in which beneficial organisms consume waste particles, similar to a land-based wastewater treatment facility.

Submerged within the biological reactor are filtration membrane fibres, which create a physical barrier between the water and tiny solid materials. Using a slight vacuum, the water is pulled through fine membranes. The water is then pumped to an ultraviolet light reactor for final disinfection. The remaining solids are pumped into a holding tank for drying and incineration, or for landing to an approved land-based facility.

HYDROXYL

The Hydroxyl system uses a coarse mechanical screen to remove wastewater solids before they enter the treatment system. The water is sent to a biological reactor, which is a system in which beneficial organisms consume waste particles, similar to a land-based wastewater treatment facility. The reactor incorporates a fixed film media, which gives beneficial bacteria a surface to attach themselves in order to aid solid breakdown.

From the biological reactor, the water is pumped to machines that mechanically and chemically remove the remaining solids from the water. This clean water is pumped through polishing filters, then sent to an ultraviolet light reactor for final disinfection. Remaining solids are pumped to a holding tank for drying and incineration, or for landing to an approved land-based facility.

EVAC

The Evac system uses a single-stream process where all the waste streams are mixed and treated together. Black and grey waters are pumped into a dedicated holding tank where wastewater hydraulic and organic peaks are equalised into one homogenised stream and passed into a mixing tank. The waste is then pumped into an efficient prescreening, where up to 40% of the solid organic waste can be removed.

Screened waste is moved into a holding tank and water is transported to a membrane bioreactor that uses submerged flat sheet membrane modules. The final clean water is removed from the membrane bioreactor through the membrane surface either by gravity or by slight vacuum. An ultraviolet system is used for disinfecting.

HAMWORTHY

A combination of biological treatment and membrane filtration processes is used in the Hamworthy system. A coarse screen removes large solid waste, which is pressed and dewatered automatically for incineration. The screened wastewater enters a two-stage biological reactor where pollutants are completely biodegraded by aerobic microorganisms. This is the same degradation process that occurs naturally in the environment. The biological reactor provides the necessary conditions to maximise the efficiency of this process.

A further stage of fine screens removes smaller solids from the biomass prior to its being passed through an ultrafiltration membrane system, which forms a physical barrier to bacteria and produces particle-free clean water. The resulting clean water is pumped to an ultraviolet light reactor for final disinfection, and can be either discharged or reused for engineering purposes. The excess solids from the biological reactor are pumped to a holding tank for drying and incineration or for landing to an approved land-based facility.