Novel Treatments Technical Note28 March 2019
PWTAG Technical notes are updates or new material for the standards and guidance given in the PWTG book, Swimming Pool Water and the PWTAG Code of practice and should be read in association with these publications.
- Subject: Novel treaments – in with the old, out with the new…
- Date: January 2011
Every year apparently new and sometimes interesting water treatment processes hit the swimming pool market – often in response to real or imaginary problems with the standard treatment methods detailed in this book.
PWTAG has endeavoured to assess these processes – not necessarily to give approval – but to protect pool operators against false claims as well as to encourage novel ideas. Sometimes this has involved PWTAG in sponsoring research – and often it involves detailed correspondence, discussions and presentations by those marketing the products. Rarely has PWTAG been able to come to a satisfactory conclusion that pleases all parties.
This is nearly always because these processes are not supported by objective data, independently verified by some recognised independent scientific body. Indeed some marketing information on new products contains misleading or pseudo-scientific data that makes the grain of truth that the process may have difficult to believe. Sometimes PWTAG has been tempted to refer such marketing data to the advertising enforcement agencies where they border on unsafe practices.
Water treatment in pools is crucial to public health – particularly disinfection. Most outbreaks of disease associated with pools are a direct result of poor disinfection processes or badly operated or broken down recommended processes. So it is essential that any process newly introduced to the industry – for public pools – be thoroughly evaluated in a scientific manner.
Simply to install new processes into pools and subjectively report that it smells good, looks good and the manager is happy, is insufficient. PWTAG is happy to advise on independent evaluation – and believes that any good process will find its way into pool water treatment. But as there is no formal regulation of new water treatment processes in the UK, guidance is given below.
What disinfection is – and is not
Disinfection can be either a physical or chemical process or a mixture of both. Physically, disease organisms may be removed, by filtration for example, or destroyed, perhaps by heating or irradiation.
Chemically, organisms can be killed by interference in their vital chemistry or sometimes rendered incapable of reproduction. the problem is that different disease organisms have different kill rates (the product of concentration of disinfectant and time) and that different disinfectants have different kill rates too.
In a pool, speed of kill is paramount to prevent cross contamination between bathers. So new processes need to quantify the rate of kill and detail that against a range of organisms.
We understand the effectiveness of chlorine, bromine (and their compounds), chlorine dioxide, etc. Some are better than others and this can be taken into account as in the preceding chapters.
But there are now many other treatments put forward for disinfection. Pool managers and PWTAG are often sent details and any prospective purchaser searching the internet for new ideas could find processes claiming to satisfy the current desire for chlorine-free disinfection or indeed chemical-free disinfection.
These tend to fall into the categories of oxidative, metal ions, electrolytic and organic compounds, where disinfection is claimed in the pool itself, and all involve chemicals. Magnetism is a physical process.
The main disinfectants are oxidising chemicals. As such they oxidise and remove pollutants including organic compounds and give a fine blue sparkling water – obviously in connection with good filtration. However, that does not mean that good oxidisers are always good disinfectants. Often the disinfection power is linked, in marketing data, to oxidation reduction potential (or Redox) of the substance. This is not necessarily linked.
The higher the position in the Table, the stronger is the oxidant or acceptor of electrons.
Peroxides (hydrogen peroxide, persulphates, etc.) are excellent at ‘removing’ by oxidation bather waste and other organic contamination and can prevent the build up of chloramines when used instead of the more customary (though not recommended by PWTAG) process of shock chlorination. But their disinfection power is poor and in general the concentration required for biocidal activity too great for swimming in.
Even oxygen is promoted as a disinfectant, where large volumes of air is pumped into the water to have a dual function to kill microbes and break down sun tan lotion, body oils, etc., with no need for other chemicals. Caveat emptor.
The generation of silver and/or copper ions has been used to disinfect small, usually domestic pools for some years; in public pools, ions alone have not been recommended, as they are not able to maintain safe bathing. More recently, ions have been used in larger pools, alongside a chlorine or bromine-based disinfectant. Silver has a slow inhibiting effect on bacterial growth.
Copper is an effective algicide, but can give considerable green-black staining problems on tiles, marbling, grout, etc. (It should not exceed 1mg/1 in pool water.) there are claims that ions and halogens together disinfect more effectively than the sum of their disinfectant powers – i.e. that there is synergy between them. There no good evidence for this, and at present the system cannot be recommended for other than domestic pools.
There is also doubt about the microbiological test methods used to support claims for copper/silver/hypochlorite systems. Silver is not inactivated by the thiosulphate normally used when collecting water samples for microbiological analysis from halogen systems. So the silver could continue to affect bacteria in the sample. If sodium thioglycollate neutraliser is not added as well, misleadingly reassuring coliform and plate counts may result.
Several systems are available that claim chlorine-free pool water disinfection. On closer reading these often call for common salt in the water: they actually are hypochlorinators. Bactericidal results may refer to the neat product from electrolyser with a few hundred ppm of chlorine. Others claim to produce oxygen products which act as a disinfectant. The results and effects claimed sometimes border on the metaphysical. it is true that electrolysis involves the excitation of several chemical species and the formation of very active chemicals and radicals.
Undoubtedly some of these are good disinfectants, but the very nature of these transient products means that are difficult to study and are not carried over into the pool itself where disinfection is at its most crucial. For these reasons they can only be classified as chlorine type disinfection for electro chlorinators and as oxygen or peroxide for the others. The residual chlorine so produced in the pool water should be treated the same as other methods of chlorine addition.
They should not be confused with those electrolysers which produce copper or silver from sacrificial anodes – see metal ions.
Often processes combine one disinfection process with another
– e.g. UV and ozone, copper and chlorine, ozone and bromine. Generally it should be assumed that the disinfection achieved is only as good as the better process – unless synergy is definitely and independently verified. Sometimes the reaction of the one process with its mate my be negative. UV will destroy ozone and ozone will produce harmful bromate from bromine present in brominated water.
A number of products have been marketed which incorporate magnets attached to the pool circulation pipe work. The claim is that they help the pool’s normal disinfection. Although some bench-scale experiments seemed to demonstrate an effect, there is no clear theoretical basis for why this should be; results on PWTAG’s pilot- scale pool were inconclusive; and there is no convincing evidence that the systems work in practice. Another product claims to soften swimming pool water and inhibit microorganisms by producing low-frequency electromagnetic radio waves. There is no good evidence for this. The same applies to a product which makes similar claims for an electronic scale eliminator.
In summary, there is no good evidence for disinfection, conflicting evidence on scale removal and water softening, and no good reason to suppose such systems could cope with large volumes.
Most new processes are old ones in new clothes. It makes sense to improve filtration, to lower chlorine residuals and improve oxidation of polluting or interfering by-products. Where operators use proven techniques to put their house in order it is clear that savings can be made on chemicals, and odours reduced. If a pool operator believes that the installer of the new process is simply fine tuning the system and that the miracle cure is irrelevant, then it probably is. Time will show which processes are really novel and become the norm in due course.