A leading ferry operator’s vessel was subject to routine public health authority testing that revealed excessive CFU (colony-forming unit) counts of bacteria in the water supply of their ferry, meaning an effective treatment solution was required for a complex, multi-source water system before the vessel was allowed to resume service. Star International came on-board the vessel to assess the situation and disinfect the water system.
Key benefits for the ferry operator:
- Removal of biofilm and water contamination
- Compliance with EU legislation
- Minimal system downtime
- No risk of corrosion to water system
- No risk of harmful by-product exposure
- Automated, constant protection
- Odour, colour and taste free - undetectable
- Marine industry recognised solution
The client's problem
Following routine tests, the water supply on a RoPax roll on, roll off passenger ferry 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.
Problems were exasperated by the fact that the vessel’s water supply was multi-source and distributed via a complex system of pipework that increased the potential for low flow and dead legs. Water sources also varied in temperature and there was a stagnation risk of the stored water due to the ship’s working cycle.
Star International’s solution
Star International was called upon treat the contamination and sent a team to the vessel to assess the situation. Before disinfection commenced, water samples were taken from both the hot and cold water systems, following the protocol described in BS 7592:1992 (Methods of sampling for Legionella organisms in water and related materials). As per the standard, a sample was taken immediately on opening water fittings, to represent the quality of water contained within the outlet, then a second sample was taken after the outlet had been allowed to run to waste, which is representative of the water quality supplied by the fitting in regular operation. For full results of the water testing, see table below.
Shock disinfection and biofilm removal
After sampling was completed work began to return the water system to a clean state via shock disinfection.
The total capacity of fresh water aboard the ship is circa 60m3 which is split across two freshwater tanks and associated pipework, the water levels in both tanks was reduced before shock disinfection. To carry out an effective disinfection, it was calculated that a Hydrogen Peroxide strength of 1000 ppm (mg/l) was required to remain in residence for at least six hours.
To achieve this, sixty litres of EndoSan 50 was added to each of the freshwater tanks via the standpipes located on deck three (120 litres in total), then it was drawn through all water outlets across all decks. Every outlet, both hot and cold, was tested using hydrogen peroxide test strip indicators to ensure the required 1000 ppm was being achieved throughout the system. After completion of drawing the solution through every outlet, a water sample was taken and analysed on-site using a tintometer which confirmed the 1000 ppm concentration. The system was then left to dwell with the solution soaking inside for the required six hours without use.
After the six-hour shock dose was completed work began to flush the solution from the system by opening all of the outlets. Test strips were used once again to ensure the solution was drained down to a residual hydrogen peroxide level of 100 ppm from cold water outlets and 50 ppm for hot water outlets. There was clear evidence of biofilm and biofouling which had been removed by the shock dose and was present in the water drained out of the hot water system (visible in Images 1 and 2 below). Particulate matter was also detected from several outlets.
Ongoing protective dosing
During and after the solution flushing procedure, both freshwater tanks were refilled to around 200m3, thus reducing the residual hydrogen peroxide concentration in the water system to 50 ppm. At this point and EndoSan Guardian Pulse Plus dosing system was installed to prevent any biofouling issues returning.
The plant room aboard the ship had previously featured a chlorine dosing system which, although had failed to maintain the water quality, did leave an injection point and water flow meter ideal for the EndoSan dosing equipment. The injector nozzle was fitted and the flow meter pulse leads attached to the constant dosing pump to ensure a correctly metered, proportional maintenance dose of EndoSan is released every 10 litres of water.
This automated safeguard provides a residual concentration of EndoSan in the system at all times preventing regrowth of bacteria and biofilm while being at a very safe level for human consumption.
Additionally, the dosage is so small it poses no threat of corrosion to the ship's water system.
EndoSan is completely free of any taint meaning it is undetectable to users with no change to smell, taste or colour of water.
Water sample results and dosing
From the sample results in the table above, it is clear that while there were no Legionella bacteria detected there was a considerable problem detected in the cold water samples before disinfection.
High TVC’s (Total Viable Count) detected with 2180 and 1240 CFU’s (colony-forming unit) per ml found in the cold outlets. These readings were reduced to <10 after disinfection with EndoSan which is the lowest level the laboratory could test to.
According to the EU's drinking water standards, Council Directive ˛98/83˛/EC on the quality of water intended for human consumption, the microbiological parameters for colony forming units or CFU/ml is required to be 100/ml at 22ºC and 20/ml at 37ºC.
As you can see at 2180 cfu/ml and ˜1240 cfu/ml this vessel’s cold water system was in serious breach of this standard.
The efficacy of EndoSan for biofilm removal and water quality control has been proven time and time again in many installations across the globe. In this case, it was shown that EndoSan is ideal for removing obdurate biofilms and returning a water system back to required EU standards, with substantially reduced Total Viable Counts.
The installation of the EndoSan Guardian Pulse Plus doing system after the system received shock treatment has also allowed the ferry operator to maintain a clean water system without any risk of corrosion or compromising the quality of the water supplied to crew and passengers 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.