Train Water Disinfection: Legionella in Train Water Systems
In 2011 it was revealed that as many as one in three trains on Britain’s rail network may have their water tanks infected with legionella bacteria. To date there has never been a case of Legionnaires’ disease associated with trains however it may only a matter of time.
It is easy to understand why legionella bacteria can breed in trains because conditions are perfect for growth. Legionella bacteria multiply in a warm, stagnant water where there is a suitable food source. Unfortunately train tanks have no access to be cleaned and the water will heat up during the summer months. In addition to this, water can become stagnant when trains are taken out of traffic.
Water is dosed from a main tank, on a depot, into smaller tanks 500 litre tanks located in the train roof space. The tanks in the train roof cannot be accessed and therefore they are never physically cleaned. Generally train tanks are disinfected with chlorine as part of an on-going maintenance regime. However this approach found to be unsuccessful at eradicating legionella bacteria.
Initial Shock Disinfection
A Huwa-San constant dosing unit was fitted to the mains supply entering the depot tank. The water from this tank was then taken to feed the train tanks. Initially Huwa-San levels were kept high at 200ppm (100ppm peroxide) to carry out a shock disinfection of the system.
Initially, it is important at that all trains get a high level of Huwa-San to ensure biofilm removal. This is because removing the biofilm ensures the lower maintenance dose is sufficient to ensure water cleanliness.
After all trains were disinfected with 200ppm Huwa-San (100ppm peroxide) then the dose rate was reduced to the normal constant dose rate of 20-30ppm Huwa-San (10-15ppm product).
Trains being disinfected with HuwaSan, using the correct procedure, are showing satisfactory levels of bacteria in their systems.