Treating Drinking And Process Water For Food Safety

During the last few decades, a wide variety of technologies have been introduced in different areas of the food and beverage industry which focus on quality improvement. Even before the harmonisation of the EU regulations was implemented, the food and beverage industry was aware of the sanitary risks as well as the economic consequences of microbiological product contamination. This resulted in the establishment of internal regulations for hygienic production in all areas.

The implementation of an HACCP concept, however, not only requires that production should be effected under perfectly hygienic circumstances, but also requires a comprehensive documentation of the operational measures necessary for that.

Chlorine dioxide is a disinfectant supporting HACCP because it can be generated on demand and the dosage can be adjusted accurately to meet varying needs. New online measuring methods make an exact documentation of the application concentration simple and safe, even in areas where the sample water is contaminated; for example in the disinfection at the cold water zone of a bottle-washing machine.

The most common pathways to spread microbiological contamination are the air, the staff, the surfaces in contact with the product (e.g. conveying belts, cutting and packing machines), and tap water. Monitoring the quality of the water is especially important, since processed products in almost any area come in contact with it, either directly or indirectly.

In the past, many factories scaled up their production capacities in an effort to meet increased demands and raise their profits. However, many of them today do not produce as much as they used to; this has resulted in cases of complex water piping systems with a discontinuous consumption.

In some pipes, the water has remained stationary for quite a long time, which would inevitably have allowed some sort of microbial build-up in the stale water. Not to mention, the material used to coat the pipes such as copper, zinc, brass, or PVC, may have interacted with the water over time, thus polluting the water. These concerns are critical from a hygienic standpoint.

Bacterial contamination in the water distribution network often occurs due to pressure variations. The formation of biofilms is another problem, especially when the piping system is old and scaling has occurred. The free chlorine content typical in the public drinking water supply has little effect on these bio-films.

Studies have showed that chlorine concentrations of 0.5-5 mg/l might be sufficient to avoid re-contamination, but in order to eliminate these films entirely, approximately 50 mg/l chlorine would have to be used.

Chlorine dioxide is capable of keeping the water distribution network very clean, because is removes bio-films already at low dosages (0.2-0.4 ppm). It is a disinfectant with a wide spectrum of activity.

In many food and beverage applications, the importance of the pH is paid too little attention. When chlorine is used, the pH plays a significant role, since above pH 7.5 approximately 50 percent of the ‘active chlorine’ has become hypochlorite which has limited microbiological inactivation power.

At pH 8, as much as 80 percent has become hypochlorite. Chlorine dioxide does not reduce its effectiveness at higher pH values but increases its performance up till pH 9.

For more than 40 years, chlorine dioxide has been used in the food and beverage industry for the disinfection of drinking and process water. It has been used since the mid-forties in America and since end of the fifties in Germany for the public water supply.

Under normal operating conditions, chlorine dioxide is a gas with a boiling point of 11 deg C. With the generation method used in our systems process, a handling of a gaseous compound is not necessary since the precursor substances are both liquids; hydrochloric acid and sodium chlorite.

The chlorine dioxide produced is in an aqueous solution. This is directly dosed in the water without intermediate storage, based on the actual demand. Therefore chlorine dioxide generators on the basis of the acid/chlorite method can also be used in the case of varying production times (8, 16, 24 hours for five or seven days per week).

Since water consumption usually varies considerably, an adjustment of the chlorine dioxide generation is necessary. This can be accomplished with a water meter connected to the generating plant. The microprocessor in the controller provides an output signal for computer monitoring of the chlorine dioxide production as well as the flow of the water to be treated.

The biggest potential for reducing the expenses for disinfectants is with in clean-in-place (CIP) systems. Peracetic acid (PAA) is widely used at 500-600 ppm and can be replaced by chlorine dioxide doing the same job at only 1 ppm. Besides chemical savings, the reduction in fresh water consumption for the final rinse adds more value. These allow for the return of investment to be typically less than a year.

The key to this application is an accurate and reliable on-line measurement, which is used to maintain a stable residual in the disinfection tank.

By means of an amperometric measuring probe, the chlorine dioxide concentration can be measured specifically and with a high accuracy even in the presence of other chlorine species (chlorine, combined chlorine, chlorite, chlorate or chloride). These measuring data are acquired in a recorder and documented.

This way, it is easy to check that disinfection has been effected properly and that the water used in the disinfection stage has sufficient chlorine dioxide concentration.

The use of chlorine dioxide for CIP cleaning offers the possibility—in accordance with HACCP—to document extensively the quality of the disinfection steps by means of automatic and continuous recording of the chlorine dioxide concentration and adjusting it to the operational requirements.