Sailing Clean: The Science of Water Treatment on Cruise Ships

Water treatment on cruise ships is vital for maintaining the safety, hygiene, and comfort of both passengers and crew. Operating like self-sufficient cities at sea, cruise ships must effectively manage several key processes, including the production of fresh water, treatment of wastewater, ensuring the safety of potable water, and maintaining recreational water facilities such as pools and spas. The SailBlue® division of Comercial Godó is designed to address these needs. By supplying chemicals tailored to these processes, SailBlue® helps cruise operators meet strict maritime regulations while catering to the unique demands on board ships.

Desalination and Freshwater Production

Desalination is a common method used by cruise ships to turn saltwater into drinkable water. Reverse osmosis (RO) and distillation are the two main desalination techniques. Certain marine chemicals are needed for each procedure to preserve the equipment and maximise the process:

Antiscalants: These are crucial in the reverse osmosis process to prevent scale formation on membranes. Scaling, caused by calcium carbonate, magnesium, and other minerals, can significantly reduce the efficiency of the RO process. Antiscalants inhibit the crystallisation of these minerals, ensuring the smooth operation of the membranes.
Coagulants and Flocculants: Used in both RO and distillation systems, these chemicals help aggregate suspended solids and fine particles into larger clumps, which can then be easily removed. Coagulants neutralise charges that keep particles separate, while flocculants bind these particles together.
Biocides: Preventing biofouling in RO systems is critical. Biocides control the growth of bacteria, algae, and other microorganisms that can clog membranes and reduce system efficiency. Chlorine and non-oxidizing biocides are commonly used, although care must be taken to ensure they do not damage the RO membranes.

Potable Water Treatment

Once freshwater is produced, it must be treated to ensure it is safe for drinking and other uses. Potable water treatment involves several chemical processes to maintain quality and safety:

Chlorine and Chlorine Dioxide: These are the most common disinfectants used to kill bacteria, viruses, and other pathogens in potable water. Chlorine dioxide is particularly effective as it does not form trihalomethanes (THMs), harmful by-products associated with chlorine disinfection.
pH Adjusters: The pH of potable water must be carefully controlled to prevent corrosion in distribution systems and ensure effective disinfection. Sodium hydroxide or lime is often used to increase pH, while sulfuric acid or carbon dioxide may be used to decrease it.
Corrosion Inhibitors: To protect the ship’s plumbing and potable water systems from corrosion, inhibitors such as phosphates or silicates are added. These chemicals form a protective film on the metal surfaces, preventing the leaching of metals like lead and copper into the drinking water.

Wastewater Treatment

Cruise ships generate significant amounts of wastewater, including greywater (from sinks, showers, and laundries) and blackwater (from toilets). Effective treatment of this wastewater is essential to comply with international regulations and protect the marine environment:

Coagulants and Flocculants: Similar to freshwater treatment, these chemicals help in the aggregation and removal of suspended solids in wastewater. Aluminium sulfate (alum) and polyaluminum chloride (PAC) are common coagulants, while various organic polymers serve as flocculants.
Disinfectants: Post-treatment disinfection is essential to ensure that any remaining pathogens in treated wastewater are destroyed before discharge. UV light and chlorine are commonly used disinfectants in this context.
Defoamers and Antifoaming Agents: These chemicals prevent the formation of foam in wastewater treatment plants, which can interfere with the treatment process. Silicone-based defoamers are typically used due to their effectiveness and low toxicity.

Pool and Spa Water Treatment

Pools and spas on cruise ships provide leisure and relaxation for passengers, but maintaining their water quality is essential for health and safety. The treatment of pool and spa water involves several chemicals to ensure water is clean, clear, and safe for swimmers:

Sanitisers: Chlorine is the most widely used sanitiser for pools and spas on cruise ships due to its effectiveness in killing bacteria, viruses, and algae. It can be applied in various forms, such as chlorine gas, liquid chlorine, or granular calcium hypochlorite. Bromine is also used, especially for spas, as it is more stable at higher temperatures and has a lower odour than chlorine.
pH Balancers: Maintaining the correct pH level is crucial for the effectiveness of sanitisers and swimmer comfort. Sodium carbonate (soda ash) is used to raise pH levels, while sodium bisulfate or muriatic acid can lower them. A balanced pH also helps to prevent corrosion of pool and spa equipment and irritation of the skin and eyes of swimmers.
Algaecides: These chemicals prevent and control the growth of algae in pool and spa water. Copper-based algaecides and quaternary ammonium compounds (quats) are commonly used. They work by interfering with the photosynthesis process of algae, effectively eliminating them from the water.
Clarifiers: To maintain crystal-clear water, clarifiers such as polyaluminum chloride or polymeric flocculants are used to coagulate fine particles into larger clumps, which can then be removed by the filtration system.

Ballast Water Treatment

Ballast water, taken on board to stabilise ships, can introduce invasive species when discharged into different waters. To prevent this, international regulations require ships to treat ballast water to kill or remove organisms:

Biocides: Similar to potable water, ballast water is treated with biocides to kill any organisms present. Sodium hypochlorite is a common choice due to its effectiveness and availability.
Neutralisers: After biocides have been applied, neutralisers such as sodium bisulfite may be used to neutralise the residual chemicals before discharge, ensuring compliance with environmental regulations.

Supplier Considerations

From a chemical supplier’s perspective, providing chemicals for cruise ship water treatment requires a deep understanding of maritime regulations, the ship’s operational profile, and environmental considerations. Suppliers must offer high-quality, effective chemicals that comply with international standards such as those set by the International Maritime Organization (IMO) and the U.S. Environmental Protection Agency (EPA).

Conclusion

Water treatment on cruise ships is a complex process that relies on a variety of chemicals to ensure safety and compliance. This includes not only the production of potable water and treatment of wastewater but also the maintenance of recreational water facilities like pools and spas. As a chemical supplier, understanding these chemicals and their applications is vital to providing effective solutions that meet the stringent requirements of the maritime industry. By focusing on quality, compliance, and customer support, suppliers can help cruise operators maintain safe, efficient, and environmentally responsible water treatment systems.