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In February 2016 microbiological examination (carried out by a local public health authority as instructed by the MCA) revealed excessive CFU (colony-forming unit) counts of bacteria in the water supply of a large ferry owned by one of the world’s leading operators. The water quality was deemed ‘unsatisfactory’ and the ferry’s day to day operational duties were severely disrupted leaving the operator facing considerable costs and loss of earnings until the problem was resolved.

The ferry in question is a ten deck ROPAX (roll-on/roll-off passenger) vessel built for transporting both passengers and freight.  

The client’s problem

The vessel operator required a solution that would improve water quality and offer long term protection, stopping the problem from reoccurring in future. Chlorine based technology had been utilised and a super chlorination of the system was tried but didn't produce the desired results due to its ‘ineffectiveness’ at removing biofilms and its corrosive nature.

EndoSan technology was identified as a potential solution due to its proven efficacy for removing biofilms, its non-corrosive attributes and its ability to achieve results at low concentrations. 

Star International’s solution

Star International surveyed the vessel and developed a two-stage plan to tackle the issues faced by the vessel operators. Objective one was to resolve the immediate contamination to get the ferry back in operation, while objective two was to put measures in place to prevent the return of the issues and avoid future problems, associated costs and downtime.

Shock disinfection and biofilm removal

The source of the water quality issue was identified as a potential biofilm therefore a shock disinfection using EndoSan50 was required. The total capacity of fresh water aboard the ship is circa 450m3 which is split across two water tanks. The water levels in both tanks were reduced prior to the shock disinfection then 40 litres of EndoSan50 was added to each tank (80 litres total to shock disinfect the entire water supply).

Following application of EndoSan the treated water in the system was pulled through all outlets on all decks starting with taps on deck 9 furthest away from the freshwater tanks in a process which took three hours. A total of 5m3 of water was pulled through from the freshwater tanks and the EndoSan 50 hydrogen peroxide concentration was confirmed at 300ppm. The solution was then left to dwell in the system for a 15-hour period.

Following the required residence time, a thorough flushing procedure was undertaken. Water was taken on board through the port hose and filled into the freshwater tanks to remove all remnants of biofilm and microbial contamination from the system. Every outlet aboard the ship was then flushed until all evidence of microbiological fouling was visually clear and EndoSan Hydrogen Peroxide levels (checked via test strips) returned to lower concentrations.

Following the disinfection and flushing procedures it was mandatory (as set by the Port Authority) to prove water quality was now in line with regulation to release the ferry from dry dock. The Port Authority instructed the same local public health authority that handled the original testing (that was deemed ‘unsatisfactory’) to attend the vessel again. Water samples were taken from multiple outlets (taps, showers, etc.) spanning all decks for laboratory analysis. A summary of the analytical results determined by the public health authority are found below.

The lab used by the public health authority to analyse both the pre and post disinfection water samples is a leading UKAS accredited lab which has a very low and therefore accurate limit of detection for the presence of Legionella in water samples, to as low as <20 cfu per litre. As shown in the results above, all water samples tested resulted in no detection of legionella and no count of legionella within the laboratory’s limit of detection (<20 cfu/litre). The public authority deemed the post shock disinfection water quality now to be ‘satisfactory’ and the Port Authority were satisfied that the operator had resolved the situation.

Ongoing protection - Constant dosing

Once the system and the water stored/distributed by it was satisfactory and clear of contamination the ferry operator was keen to put measures in place to prevent a problem of this magnitude occurring again. To tackle this a EndoSan Guardian Pulse Plus dosing system was installed and commissioned on board and the ongoing use of EndoSan to control water quality began.

The EndoSan Guardian Pulse Plus dosing system is an automated dosing system which injects EndoSan directly into the water system using a signal from a water flow meter to ensure effective proportional chemical dosing.

Following installation and with the water flow rate being monitored by the dosing system an automated, precisely controlled residual level of EndoSan is released into the water system safeguarding it against the return of microbiological contamination.

The EndoSan being dosed into the water system is at a concentration high enough to prevent the regrowth of bacteria and biofilm whilst also being a very safe level for human consumption.

Additionally the low concentration dosage provides no risk of corrosion to the ships water system and with EndoSan being free of taint it is undetectable to users (no change to smell, taste or colour of the water).


The efficacy of EndoSan for biofilm removal and legionella control have been proven time and time again in many installations across the globe. In this case it was shown that EndoSan is a far superior biocide than Chlorine based technologies and thus removed obdurate biofilms where super chlorination could not. EndoSan is also non-corrosive, odourless and tasteless making it the perfect, environmentally sound biocide, for water treatment on board shipping vessels.

The installation of our Guardian Pulse Plus dosing system has also allowed the customer to maintain a clean system with a fully sanitised, safe, water supply on board.

EndoSan is a globally recognised, trusted technology that is being utilised by the marine shipping industry to ensure that vessels have a clean, safe water supply from a cost effective, approved water treatment solution.

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