Descaling Watercoolers

Several products are available for descaling watercoolers. These are based on acids with optionally other components, such as wetting agents and colours. The choice of product depends on the preferred method employed to descale coolers.  If the spring water is very high in salts based on calcium and magnesium, you will see hard water residues in the cooler reservoir. These residues are fairly easy to remove with acids.

The speed of removal depends on the concentration of the acid and the temperature of the water. Some operators prefer to use concentrated acid to obtain removal in seconds.  This is OK but requires careful rinsing of the reservoir, best checked with pH indicator paper. An alternative is to use diluted acid (safer) and leave for a short soak in warm water.

The heater coils from the hot tank require a stronger acid because build-up is much worse in his part of the cooler. Never use oxidising acids such as nitric acid or chlorinated acids, such as hydrochloric, otherwise there is considerable danger of corrosion on stainless steel parts.  The most cost-effective acids are based on phosphoric. Wetting agents may help with penetrating thick residues, but beware of foaming during use. Colours added to acids can act as a trace to reveal unremoved scale.  However, the best all-round product is a simple acid.

Green (algae-contaminated) Polycarbonate Bottles

The season for green polycarbonate bottles will arrive soon in the Northern hemisphere and has never left the warmer countries. It is important to emphasize the need for effective bottle washing.   Most of the soiling on a returned bottle is on the outside of the bottle.  Even a thin layer of dust can contain algal spores. This means that the tank of the washer will soon become contaminated.

The environment in the washer should be made as inhospitable as possible for the spores. Temperatures should be kept high, around 65 degrees C, but not too high that bottle damage can result (70 degrees C and above), detergent concentrations should be maintained throughout the shift with top-up as required. Use products containing a “real” detergent rather than just water softening components.

Bottle wash products are now available containing biocide, as well as regular detergent components (eg, Liqualin Safeguard) which will help in the fight against algae.  Always use a peracetic acid rinse after the wash and a final rinse with ozonated water, if this facility is available. Remember to always dump your wash tank at the end of the shift and flush out the inside with more peracetic acid.

Finally, you need to be ruthless in discarding green bottles that come into your plant for washing.

Ozone Exposure in the Bottling Plant and Measurements

The UK Health & Safety Executive has laid down guidelines for operators exposed to ozone during their working day. These are as follows:

Exposure                 Ozone Level
Max 8 hours         0.067 ppm
Max 5 hours         0.1 ppm
Max 15 minutes         0.3 ppm

0.1 ppm is equal to 0.2 mg ozone per cubic metre of air.

Ozone monitors are available which constantly measure the ozone level in the work environment within the bottling plant. The ozone concentration is shown by a multi-coloured graphical display from green (safe) to yellow (caution) to red (danger). No installation is required and operation is simple. The unit works on batteries or mains supply.  Normal range of detection is from 0.02 - 0.14 ppm.

For those not wishing to invest in a meter, cards are available which may be carried by the operator. Each card can register exposure to ozone by a colour change at 5 different zones on the card.

Measuring Ozone in Water

The method used by many bottling plants involves a colour reaction.  Ozone reacts in weakly acidic solution with dipropyl-p-phenylenediamine (DPD) to form a red-violet dye. The ozone concentration is measured semi-quantitatively by visual comparison of the colour of the measurement solution with the zones of a colour card.  The method is not very user friendly and needs carefully adjustment of pH, mixing of two reagents and  visual comparison of colours.  However, simple, low-cost dissolved ozone meters are available. These measure dissolved ozone in 50ml or 180ml samples. The sensor does not contact the water, so there is no special probe installation. The unit is easy to operate and calibration can be checked by standard kits or ozone sources provided by the manufacturer. The unit can be used with rechargeable batteries or mains application. There are two measuring ranges: 0.02 - 0.14 ppm (mg/l) and 0.1 - 0.7 ppm (mg/l). Accuracy is about 20% and response time between 10 seconds and 1 minute.

If you need a quick, semi-quantitative test, then simple dip strips may be used.

What Affects Water Taste?

Water taste can be very subjective. Some people have blind spots when it comes to detecting flavours in food but you would think that water should not present any problems.  However, this is not always the case.

In a water tasting, some time ago, connoisseurs of wine tasting tried many different waters.  Second position after Evian was tap water.  Now, at the time, there was some hint of unfair advantage for the tap water because it had been slightly chilled.

It is true that temperature of the water is very important in appreciation of the taste and this parameter needs to be constant in any side-by-side comparison. The total mineral content and type of minerals present also exert a profound effect on taste.  I must admit that my favourite is San Pellegrino and this has a huge mineral content.  Evian, on the other hand, is fairly low on TDS.

Iron content exhibits a strong influence on the taste giving a noticeably bitter after-taste.  Bicarbonate also gives a very characteristic chalky taste, although food connoisseurs will tell you that this is a preferred taste in water for the accompaniment of food.  In some  bottling plants I have seen the taste-test for ozonated water being done immediately after taking a sample from the line.  The panel of tasters actually have been trained to ignore the taste of ozone in determining the taste of the water.  They certainly will not suffer from bad breath problems!

Microbial Contamination in Mains-Fed Coolers

Microbore tubing can be a source of microbial contamination in mains-fed water dispensers.  Frequently used dispensers normally do not have any problems because the water in the microbore is displaced frequently.  It is better to have only short lengths of microbore feed whenever this is possible, for example, less than 2m.  However, sometimes this is not possible and microbore tubing lengths in excess of 20m can be found in some locations.

This is not necessarily a problem, provided the dispenser is used often and the microbore in not in a warm environment (greater than 21 degrees C).  Problems have been seen with only short lengths of microbore tubing when dispenser usage is infrequent, for example, in a meeting room environment where meeetings are infrequent and tea and coffee are readily available, the water dispenser may not be used for days at a time, and not used at all at the weekends.

When water is sitting in a microbore for days, the chlorination protection will dissipate and any surviving bacteria will begin to multiply, forming a biofilm in the ideal conditions of warmth and with a polyethylene substrate.  A great lover of biofilms is Ps. aeruginosa and this bacterium will rapidly assist in the formation of the polysaccharide-rich film.  The biofilm sheds bacteria consistently, contaminating the cooler, despite repeated sanitisation.

Therefore, when surveying locations for coolers, always try to obtain an idea of frequency of use.  It may even be more appropriate to install a bottled water cooler.  However, if a mains-fed cooler is installed under conditions where use is limited, always dispense at least 1 litre of water every Monday morning and consider replacing the microbore tubing every 6 months or at least every year.