Tuesday, 22 January 2013

Sanitising Sealed Mains-Fed Water Coolers

Sanitising sealed mains-fed water coolers can be difficult but not impossible.  The main issue is how to get the descaling and disinfectant liquids into the unit. Typical units are the direct chill or spiral chill type.  Frequency for sanitising and filter changes is every 6 months.

The filter housing can be disconnected from the microbore tubing and a small device known as a venturi doser put in its place.  The doser is filled with the recommended amount of descaler and the hot tap actuated.  This will draw descaling acid solution into the tank.  After descaling, flush with at least 4 litres of water and test with pH paper until neutral.

The spiral chill pathways can be descaled and then disinfected using the same technique with respectively phosphoric acid (for example) and hydrogen peroxide.  The chemical is drawn from the doser by actuating the chill tap.  When the chemical begins to run from the tap (you can check this with pH paper or peroxide test strips), turn the tap off and wait for ten minutes.  Then flush with water until the test strips are clear.

This is not a detailed procedure and coolers vary considerably in design, however it will serve as a guideline.  Always check with your cooler supplier if in doubt.

Descaling and Disinfecting Water Coolers

The hot tank of coolers can be descaled using an acid such as phosphoric or citric. Sometimes other internal  parts of coolers need to be descaled and disinfected.  Scale build up in reservoirs, for example, is usually not severe but can lead to microbiological problems if left.  Attachment of micro-organisms and ultimately formation of a biofilm can rapidly cause deep-seated contamination which is not always easy to remove.

It is common practice to use a descaler, accompanied by mechanical action such as brushing, followed by a disinfectant such as hydrogen peroxide.  This will remove the scale and destroy the biofilm.  In some practices it is considered that one application of acid is sufficient to descale and destroy biofilm.  This is not always the case and is very dependent on the strength of acid used.  Very strong acids will do the job but these are usually applied diluted.

Diluted acids will remove scale more slowly and much of the acid is used up in this process.  In this case biofilm will not be removed.  If you want to use acid alone, then either use very strong acid (not recommended from a safety point of view) or use the acid in two steps, one to descale and the other to kill bacteria.

An alternative is to use an acid containing a disinfectant component which can then act as a sanitiser while removing scale.  These are available on the market.  However, the preferred method is to descale and then disinfect, in two separate steps.