Cleaning Drinking Water
Until surprisingly recently, there were essentially no set water quality standards for drinking water and water to be used for use in food/drink manufacturing, by the mid – 20th century there was guidance on microbiological quality, using E.coli as an indication organism. The reason this bacteria was used was it was taken that any treatment was deemed inadequate or the water had been contaminated with faecal organisms. Sadly so much of the world’s drinking water still fails this standard, particularly in densely populated areas such as India and South America.
The World Health Organisation (WHO) was instrumental in trying to set standards for drinking water and in turn the European Commission (EC) in 1980 published its first Drinking Water Directive, which was later incorporated into British law in 1988. In 1998 the EC Directive was updated (98/83/EC) and again as the UK legislation was classed as an enabling law, it has also been updated, and incorporated into law by the various governments within the UK. The latest review of the EC, now termed European Union (EU) directive was in June 2011; however no amendments were made to the 1998 directive. Since then in Dec 11, the various UK governments have released a document called ‘Water for Life’ a White Paper on the future of drinking water quality in the UK.
In the UK, unlike other services, such as gas and electricity, a national network does not exist for the distribution of water. Since privatisation of the water companies, is it very unlikely this will ever come to exist, therefore whilst the west of the UK has relatively few problems with its supply of drinking water, doubtless to the east and particularly the south east, where nearly 25% of the entire UK population lives, there will be problems not just with sourcing water, but also cost wise to clean it to acceptable standards, particularly in the so called food counties such as Norfolk, Suffolk and Lincolnshire.
Although new treatment processes are being developed, the basis of water treatment for drinking water and water used in food/drink industries is still fairly similar across the UK
- Coagulation - where the undissolved solids are destabilised, usually with an inorganic coagulant such as Aluminium Sulphate
- Flocculation – a polymer is added to assist the coagulant in blinding the solids together more rapidly
- Solids removal – either by settlement by gravity or by floatation using aeration
- Filtration – Usually sand filtration that polish any remaining solids left by stage 3
- Disinfection – usual a halogen based chemical, such as chlorine gas or sodium hypochlorite, due to their cheapness.
There are important variations to this treatment, mainly to meet local requirements, for quality and depending on the source of the water, for example in the east of England it is not uncommon to see activated carbon (GAC) and Ozone used in the treatment of drinking water, unlike the west and north which has large reservoirs, the water used in the east of the UK is sourced from lowland surface water. The reason therefore that these lowlands waters are more likely to have to incorporate these additional stages, such as Ozone, is that the water source is likely to have come into contact with pesticides and herbicides, which would not be taken out by the general process outlined above. Therefore the addition of these additional stages helps to ensure that the contaminates are removed.
Where high levels of water ‘salts’ or metals might be present in the water table used for extraction, such as iron and magnesium, the older method for removal for these contaminants is to use a combination of filtration and chemicals, such as acid to form insoluble forms of the salts and then disinfection, again normally hypochlorite.
Most of the new systems used mainly by industry using a local water source, will now incorporate systems which incorporate the use of some kind of membrane. The most popular of these would be Reverse Osmosis, (RO) these are usually seen as banks of tubes, which are filled with cartridges of semi-permeable membranes, typically sized at 0.5nano metres (nm), these allow water through but block the impurities from passing through. If producing for some of the major food groups such as Marks & Spencer (M&S) or Tesco, then some sites are required to incorporate even finer filtration, this is normally termed Ultrafiltration, with membranes down to lower than 0.1um; this is to take out bacteria such as Cryptosporidium. There has been some work on cleaning up suspected groundwater, with the use of electro-coagulation and permeable reactive barriers, however their general use in the UK is not that wide-spread and they have proved expensive to use.
There are a limited of situations in the UK where sites recycle water, and there is little doubt that this will develop more as water becomes a more costly commodity, sites where this is being introduced tend to be in towns and cities with limited water supplies and when sites wish to expand they find they are unable to increase their water consumption from the local supplier and have to look at recycling. Most of the current uses for recycled water are in areas that have no direct contact with food/drinks products, such as boilers, cooling systems, vehicle and general wash-down water
Whilst the UK has in the main the plentiful supply of water to use for drinking, there is little doubt that in certain geographical areas, and for certain industries there will continue to be significant investment in water treatment, which might not always deliver a quick Return on Investment (RoI) but do allow companies to remain operational especially during periods of drought.