Ensuring water quality in food processing

Water is used in food processing for many different purposes. Among other applications it is used in direct contact with the food or food contact surfaces (as an ingredient, steam, etc) or indirectly as a processing aid. Therefore, water quality used in a food manufacturing plant has to be managed not only with respect to product safety, but also in view of the capability of production processes (e.g. cooling, heating and cleaning). A further aspect is the safety of the personnel in the workplace (e.g. canteens, showers). This article summarises the main hazards and potential effective treatments to ensure an adequate water quality.

Water has been increasingly looked at as a valuable resource and its quality (and in this respect also safety) cannot be taken as granted. This has also been recognised by requiring the application of HACCP principles in the water usage1,2. Potential physical, chemical and biological hazards introduced by water shall be adequately controlled, which necessitates water treatment when entering a food plant in many cases to ensure potable (drinking) water quality where needed. In case non-potable water is used, it shall be evaluated as part of the HACCP studies to ensure that it would not pose a risk for production, and has no negative effect on personnel.

For a comprehensive reading about hazards related to incoming water, reference is made to the WHO guidelines for drinking water quality3.

Sources of contamination

Physical hazards derived from incoming water are usually controlled by filtration (if necessary), and its effectiveness can be monitored by turbidity measurements. Chemical hazards include organic compounds, many contam – inants (e.g. pesticides) and elements (e.g. heavy metals), which are mentioned in detail in the EU drinking water directive4 and the above mentioned WHO guidelines.

Biological hazards not only include the organisms of concern, but also the con – sequences of their presence, e.g. toxin formation by some types of algae. Waterborne micro – organisms potentially causing illness include bacteria, viruses, protozoa and helminths. The resistance / susceptibility of those organisms to commonly used treatments and the way of transmission needs to be considered to ensure water quality. Most of the pathogens are introduced into the water by animal and / or human sewage and do not grow in water. However, some are environmental pathogens that can grow in water. One example is Legionella, which is transmitted by inhalation / aerosols, leading to an infection of the respiratory tract. The risks related to Legionella have to be considered with respect to personnel safety (showers / washrooms), and as well to the wider environment of the plant when, for example, cooling towers are used from where water can spread into the wider surrounding5. Due to the growth characteristics of these bacteria, water temperatures below 20°C and above 60°C would prevent multiplication in the system6. The European guidelines6 also provide information with respect to effective treatments / disinfection of water systems.

Table 1: Most common treatment techniques in relation to the hazards that need to be controlled

In general, water quality controls should start at the source, and also include the review of incoming / used municipal water supplies. The history of drinking water supplies should also be taken into account, e.g. known outbreaks related to the water supply or boil water notices, when considering treatment options to ensure water quality. More detailed information to the effectiveness of treatments commonly used in the food industry can be found in ‘Foodborne viruses: An emerging problem’7, ‘Foodborne Protozoan Parasites’8, ‘Water quality for the food industry: management and microbiological issues’9 looking specifically at Legionella and Cryptosporidium, and more general in ‘Considering water quality for use in the food industry’10.

Design aspects of storage and distribution in a food manufacturing facility12

Effective microbiological controls include the hygienic design of the water distribution and storage systems. The same general principles should be followed as for food manufacturing equipment, such as dead ends and stagnant areas are avoided, prevention of biofilms and scaling is ensured, and ensuring that the entire system can be cleaned and disinfected as needed on a regular basis. All materials used for fittings, pipes and tanks shall be compatible with the conditions in the system, which includes the resistance of the materials used against cleaning and disinfection agents.

A break at the entry point of the facility should be present to prevent any backflow.

Storage tanks should be enclosed to prevent any contamination by pests or extra – neous matter. Vents should preferably be equipped with an air filter to achieve air filter class F7. At minimum, an insect screen should be installed.

The tank design should allow for full drainability when emptying it and the entire system should preferably be designed such that the maximum residence time of the water does not exceed 24 hours.

Water treatment11

The choice of the most suitable water treatment technique depends on the water source, the design of the system and the intended application of the water.

As indicated above, the water storage and distribution system design should allow for cleaning and disinfection. In reality, this is quite often an issue and cleaning is hardly possible. So typically, the water is treated at the point of entry into a food manufacturing facility and the quality is maintained and monitored within the factory. The microbiological quality of water is monitored at different points in the plant, including last points of pipes, and appropriate treatments are applied. Often a combination of techniques will be necessary to meet the demands.

In Table 1, an overview is given of the most common treatment techniques in relation to the hazards that need to be controlled.

Filtration

With dependence upon the contamination risk, it might be required to pass the incoming water through a filter that retains solids (e.g. for well water).Filtration methods range from porous filters for larger particles to membrane filtration to retain smaller suspended particles and even microorganisms (reverse osmosis). The risk of microbiological growth needs to be considered when filters do not constantly receive water. Therefore, a continuous recirculation of the water is recommended, if no water is consumed.

Chlorination

Chlorination is the most common chemical oxidising method used for disinfection of water systems. It is used as hypochlorite solution (liquid bleach) and chloride dioxide. The advantage is that chlorine is relatively inexpensive and that automated systems and generator do not require a lot of capital investment. A residual concentration of minimum 0.5 mg/l free chlorine for at least 30 minutes (pH<8) should be maintained for an effective disinfection.

Hypochlorite reacts with the nitrogenous component of organic substances. This means it will be used up during this reaction. Automated systems for continuous water chlorination are available. The main disadvantages of hypochlorite are that it is highly corrosive in its undiluted form, may form unwanted byproducts (chloramines, chlorophenol) and will be used up easily by organic matters.

Chloride-dioxide is a very unstable gas and must be generated at the point of use. It has some advantages versus hypochlorite such as being less corrosive. The effectiveness to tackle biofilms is higher compared to hypo – chlorite and thus this is the preferred method for chlorination.

Electrochemically activated water

Recently, treatment with electrochemically activated water has become more and more popular. An electrochemical cell produces a highly oxidised fluid (anode) and a reduced fluid (cathode) using just water and salt. The cell may be separated by a diaphragm. The oxidised fluid has high oxidation-reduction-potential (ORP) of up to +1300mV (chlorine based solutions have up to +800mV). The solution is meta-stable for up to a couple of weeks and like chlorinedioxide generated onsite. The disinfectant contains mainly hypochlorous acid and smaller amounts of chlorine dioxide and ozone and small quantities will be dosed into the water system. It should be noted that manufacturers claim that this is a chemical-free method for water treatment. But in fact it isn’t, even though concentration of chemicals is extremely low and the working principle is rather based on the ORP than on the chemicals.

Ozone

Like chlorine dioxide is not stable and must be generated onsite. It has a very high ORP above + two volts and thus a high capability for disinfection with a broad spectrum of activity, viruses inclusively. Due to its good water solubility, it is very suitable for the disinfection of water systems maintaining a concentration of 0.4 mg/l for five minutes (in the presence of spores 2 mg/l). The main disadvantages are that it will be used up easily by organic matter and the energy costs to produce ozone are fairly high. Ozone should not be used in evaporative cooling systems due to its volatility.

Ultraviolet radiation (UV)

Microorganisms are being inactivated by short wave UV light (UV-C, 100 – 280 nanometre wavelengths). The nucleic acid will of the microorganisms’ cells will be damaged and with it the DNA during the treatment. The UV light source is enclosed in a transparent protective sleeve and installed in a way that water can pass through a flow chamber.

Suspended particles may protect micro – organisms (‘shadow effect’), so the effectiveness of the treatment very much depends on turbidity, adsorption and concentration of particles and organic materials. Otherwise, UV treatment could ensure up to a 4 log reduction, but will never lead to obtain sterile water. Also the removal of biofilms will not be possible, as the treatment is only done at the UV light source, but not throughout the system. The advantages are that this treatment is chemical free and that it has a broad spectrum of activity.

Post water treatment requirements

Some of the treatments above require another step, like neutralisation or adsorption of organic matter or odours using activated carbon.

References

1. Codex Alimentarius – Food Hygiene – Basic Texts – Second Edition, Rome 2001: http://www.fao. org/docrep/005/Y1579E/y1579e00.htm

2. Regulation EC 178/2002

3. WHO, Guidelines for Drinking water quality, 4th Edition, 2011

4. Council Directive 98/83/EC

5. Outbreak of Legionellosis in Spain, Pamplona, 2006 originating from cooling towers www.promedmail.org

6. European Guidelines for Control and prevention of travel associated Legionnaires´disease http://www.hpa.org.uk/webc/HPAwebFile/HPAwe b_C/1274093149925

7. M. Koopmans, E.Duizer “Foodborne viruses: An emerging problem” Int. J. Food Microbiol. 90(1): 23-41 (2004)

8. D. Dawson “Foodborne Protozoan Parasites” Int. J. Food Microbiol. 103(2):207-227 (2005)

9. “Water quality for the food industry: management and microbiological issues” CCFRA Guideline No. 27 (2000)

10. “Considering water quality for use in the food industry” ILSI Report, April 2008

11. EHEDG Guideline 28 “Safe and hygienic water treatment in food factories” (2004)

12. EHEDG Guideline 27 “Safe Storage and Distribution of Water in Food Factories” (2004)