Sanitisation is a crucial and constantly changing
Sanitisation is a crucial and
constantly changing element of pool maintenance. In this feature, SPLASH! asks
a number of experts about what is tried and true, what is new and exciting, and
what is just around the corner corner.
Sanitisation
occurs in conjunction with filtration and pool cleaning to keep the pool water
clean and free of dangerous organisms. This feature article is largely about
sanitisation in general, and so covers both residential and commercial aspects
of this topic. Industry experts have expressed a number of opinions and
technical viewpoints in this feature.
The case for chlorine
William Bliss of
Wobelea is a water sanitisation expert dealing with swimming pools, air
conditioning towers and food production and export.
Here, he offers some thoughts on the forms of pool sanitisation that are proven
to work and will continue to be accepted as time goes on. His article largely
relates to commercial pools, but is equally relevant to the residential
industry, especially with the move to more heated indoor pools, and the
increasing battle with chloramines.
Dr Tom Lachocki
at the recent Gold Coast Expo did not hesitate to reinforce the position of
chlorine as the most cost effective sanitiser both in commercial and domestic
pool operations. Looking at the list of currently APVMA-registered pool
sanitisers, the vast majority are chlorine-based. A lesser number of
bromine/chlorine products are specifically aimed at the spa pool and
hydrotherapy area. The anti-chlorine lobby are happy to decry chlorine as it
“destroys the ozone layer”. Chlorine as a gas, yes. Chlorine as hypochlorite
does not have an equal level of volatility or chemical clout as the gas. As a
commercial or domestic disinfectant, chlorine gas is no longer used in Australia.
The ozone and
chlorine dioxide promoters are happy to point out that their respective
products are more effective than chlorine against cryptosporidium. “Crypto” is
a very unpleasant and virulent organism capable of making a commercial pool
unusable for up to 24 hours.
Regular slug
doses of chlorine dioxide are suggested by additions of “stabilised chlorine
dioxide”. Ozone units are in general run in combination with a chlorine dosing
system; not so much for crypto control, but to provide a “residual of chlorine
in the pool water” as required under State Health Regulations.
The other facet
is the production of chloramines. Chloramines are formed when chlorine reacts
with organic matter in the form ofhuman waste products such as perspiration,
urine or faeces. If the pool or spa is topped up or filled with surface water
from a dam or creek, then we have even more organic building blocks for other
types of chloramines. The main problem with chloramines is the effect of eye
irritation, odour complaints and structural corrosion.
Currently
chloramine reduction is based on two approaches best described as “dump” or
“thump”. The “dumpers” recommend removing pool water and replacing with fresh
water. The technique uses more water and more energy to heat the cold fresh
water to a comfortable level. The “thumpers” use shock doses of chlorine up to
10ppm in an endeavour to burn out the offending chloramines. While this
approach may work with simple ammonia based chloramines, it is unlikely to
succeed in removing more complicated organics – in fact, it may make the
situation worse.
A rule of
chemistry is based on the square of the concentrations of the reactants. Hence,
if we double the chlorine level, we stand to get four times the yield of
chloramines. This is a good example of “more is not better”. More chlorine =
more chloramine.
What options
exist? Filtration as “flocculation filtration” is effective in reducing the
quantity of long chain organics by trapping these compounds in the filter. To
be effective, it may require filtration speeds of 20-25m/hr, that is, half the
normal speed of high rate sand filters. If space in the plant room permits,
install a second filter to match the existing one. For filtration, split the
existing pump discharge to two filters. Flocculant is introduced on the suction
side of the pump. For backwash, use changeover valves to have all the pump flow
directed to one filter at a time.
Another option
is to oxidise the organics before the chlorine dosing stage. A variety of
oxidisers can be used such as ozone, peroxide, chlorine dioxide and
persulphate.
My own personal
observation of swim schools indicates that the use of chlorine dioxide at
0.2ppm with chlorine at 1ppm is quite effective, and combined with flocculation
filtrations, gives an excellent result. One particular 50,000L pool in a Melbourne bayside suburb
has twin skimmers connected to 2 x 0.7m HRS filters. The swim school operates
six days per week with a bathing load of 100 children below 6 years of age
every day. Following a history of chloramine and clarity problems, we were
asked to develop a treatment program to fix the problems.
Being aware that
previous actions such as “dumping and thumping” were ineffective, we made
contact with Wapotec in Salzburg,
Austria, for
specific advice. Wapotec listed the following points:
1. Reduce the
filtration speed to 25m/hr;
2. Add a 150mm
bed of anthracite on top of the filter sand;
3. Provide a
flocculant injection before the filter;
4. Combine
simultaneous injection of chlorine dioxide and chlorine.
Since introducing
these changes in 1996, eye irritation and chloramines have been kept at
acceptable levels.
To look at
sanitation as a single chemical based issue is not practical. Filtration issues
must also be incorporated to provide an effective
integrated approach.
Chlorine choices for residential pools
Jayne Rokesky of
Focus Products gives a brief rundown of the different methods of getting
chlorine into a residential pool
Total water
balance ensures that the water is safe and comfortable to swim in. An important
aspect of this is the sanitation of pool water or the production of FAC (free
available chlorine). Residential pools are built in a variety of sizes ranging
from 10,000 litres to 200,000 litres and have finishes as varied as vinyl
liners, fibreglass, pebble and tile. The consumer faces a large task when
deciding which sanitation system is best for them. It is necessary for the pool
professional looking after the customer to know what the bather load is like,
where the pool is located (that is, indoor
or outdoor; heated or not; plus other information).
All these
constituents have an effect on the availability of FAC. A variety of options
are available for the job. A large majority of pools within Australia
operate salt chlorinators. In recent years these have become more advanced with
the introduction of “self cleaning” or reverse polarity cells. A “chlorine
factory” within your pool! Other sanitation options are calcium hypochlorite
(70% available chlorine) which is added to the pool on a daily basis. One of
the drawbacks off this method is the climbing calcium levels that eventually
occur and the high pH of the product causing an acid demand.
Sodium
dichloroisocyanurate also known as stabilised chlorine (60% available chlorine)
which is added to the pool every second day. This is one product that has
minimal effect on the water chemistry due to its pH of 6.5. Sodium
trichlorisocyanurate, also known as pool tablets or once a week tablets (89%
available chlorine), is generally added on a weekly basis depending on size of
pool and bather load etc. These tablets can be added by a floater or an inline
feeder. In some instances these tablets are available with their own disposable
floating dispensers and have the addition of copper for algaestate properties and
clarifier for crystal clear water.
Calcium
hypochlorite tablets are for those people who want the convenience of a tablet
without the addition of stabiliser. This makes them ideal for indoor pools and
water features. Sodium hyresidential
pochlorite
(10%-13% available chlorine) can also be used and automatic feeding systems
have been introduced to make the application a little easier for the consumer -
“set and forget”. The liquids are fed at approx three-minute intervals,
ensuring that the chlorine is monitored and adjusted regularly. It is important
to ensure that the drums have adequate chlorine and hydrochloric acid in them
at all times. In addition to this, it is possible to run ioniser systems which
work on silver (bactericide) and copper
(algaestat) with a minimal dose of additional chlorine. It is also imperative
to remember that unless the other relevant water parametersare correct then
chlorine will not work effectively.
The ideal system
to ensure that the pool user has the safest water possible is to combine their
sanitation program with a preventative algaecide and regular oxidation system.
The filter should be chemically cleaned at least twice a year to remove the
build-up of body fats and oils. This will aid the chemicals in providing safe and
bacteria-free water. A lot of questions will go a long way in ensuring that the
consumer is provided with a system that fills their expectations and looks
after their water.
Salt water pools
Jake Brandish of
Monarch Pool Systems, manufacturer of the Chloromatic salt water chlorinator,
writes about the benefits of salt.
Owning a
swimming pool or spa brings great enjoyment and health benefits to the owner
and their family, but is a great responsibility. It not only requires understanding of safety
and first aid, but also a basic understanding of chemistry and chemical
treatment of the body of water. Unless this body of
water is safe to swim in, the bather may be in danger of illness. Many people
do not realise that chemicals used in this everyday chore are dangerous and
care should be taken when handling them. These chemicals should never be mixed
together or added in proportions other than those stated by the manufacturer.
Chlorine is the most common sanitiser used in pools. It is a complex chemical
compound, is classed as a
dangerous good, is bulky to transport and store and should be used with extreme
care. This is the contributing factor why the majority of pool
owners have chosen to install a salt water chlorinator on their pools to manage
the daily dosing of chlorine. Chlorine is the globally accepted means by which
water is sanitised for bathing, drinking, etc.
A healthy pool
requires a daily dose of this chemical to control the growth of bacteria and
algae, and therefore prevent higher than acceptable levels of contamination.
Chlorine sanitises the water, the filter then filters out the dead or dormant
particles for removal from the filtration system.
Instead of
adding this chemical manually, a salt water chlorinator will actually
manufacture chlorine from common salt. Salt is added to the pool to achieve a
salt level of around 5,000ppm (parts per million). The ocean has an average
salt level of 38,000ppm, so it can be easily seen that a salt pool is much less
salty than the ocean. Salt usually costs around $7 per 25kg bag and is readily
available from the local pool chemical supplier. The average pool requires
around 200kg of salt on its initial dose. The salt is not ‘consumed’ in the
chlorination process, but is ‘recycled’ for continual production of chlorine.
The salt water chlorinator then electrolyses the chloride element of salt
(sodium chloride) and converts it into
the sanitiser known as chlorine. Salt should then be ‘topped up’ by adding
approximately 1 x 25kg bag per quarter. Salt is only lost by the loss of water
out of the pool, such as backwashing and splashing.
There are many
advantages to this process. Cost effectiveness and convenience are the main
reasons why the majority of pool owners choose salt over any other means of
sanitising their pool. It has been found that a salt water chlorinator will
produce chlorine at around 10% the cost of buying the chemical. Couple this
with the convenience of never having to purchase chlorine, let alone having to
add it to the pool, and it is easy to see why
salt systems are so popular. There are of course ongoing maintenance costs (as
there are in most equipment or machinery) but even then, the pool owner is way
ahead. The prime cost involved with a salt system is the replacement of the
electrode, which starts from a few hundred dollars. This electrode generally
lasts an average of 3-5 years, but if the equipment is maintained and looked
after, this life expectancy can
be easily increased.
The other
advantage of using a salt water chlorinator is the comfort to bathers. The
human body is made up of around 80% fluid – most of which is saline. This makes
a salt pool a perfectly natural environment for the body to be in. The salinity
of saliva or tears ranges from 7,000ppm to 9,000ppm. It is also said that a salt
pools’ water feels softer – this may be due to the nature of the salty
environment the body is in. Installing a salt water chlorinator is a simple
case of mounting the power pack onto the nearest wall or post, and plumbing the
electrolytic cell housing into the return to pool pipe work after the filter.
Most salt water chlorinators incorporate an in-built timer which controls the
main filter pump as well as the chlorinator as the two must run together.
Units are also
available with pool light transformers and even pH monitoring and dosing. These
units make the owner’s maintenance minimal because the pH is directly related
to the effectiveness of the chlorine in the pool. If the salt water chlorinator
can monitor and dose pool acid levels to achieve a constant pH level, the
chlorine will be able to do its job far better than a pH level that is allowed
to fluctuate.
Ozone swimming pool and spa sanitisation
Phillip Green,
director of the Ozone Layer, Australian distributors of the Del Ozone range,
talks about the benefits of ozone systems.
Despite it
having been used to purify water since the 1800s, there are still many
misconceptions regarding ozone as a sanitiser. Let’s look at a few questions
that are commonly asked about ozone and its effectiveness. What is Ozone? Ozone
is active oxygen, O3. It occurs naturally in the earth’s
atmosphere to protect us from the sun’s harmful rays. Ozone is created in
nature by the combination of oxygen in the air and ultraviolet rays of the sun
or by the corona discharge during a lightning storm. Oxygen molecules (O2) are
split by adding energy, resulting in two individual oxygen atoms (O1); they
unite with other oxygen molecules (O2) to produce (O3). (O1) + (O2) = (O3). The
third oxygen atom is held by a very week single bond and an oxidation reaction
occurs upon any collision between an ozone molecule and a molecule of an
oxidisable substance. The weak bond splits off leaving oxygen as a by-product
and during the oxidation reaction, organic molecules are changed, dissolved metals
are no longer soluble and chloramines and other chemical by-products are broken
down.
How is Ozone
produced for Swimming Pools & Spas? Ultraviolet (UV) light and Corona
Discharge (CD) are the two methods. For UV, a special lamp gives off a specific
wavelength of ultraviolet light which converts oxygen (O2) molecules into ozone
(O3) molecules by splitting the oxygen molecules into individual oxygen atoms
(O1) which then recombine with oxygen to form ozone. This all occurs instantly
inside the ozone chamber in the
ozone generator. With CD, ozone is produced by passing air through a high
voltage discharge, or corona. Air or concentrated oxygen dried to
a minimum of -60C dew point passes through the corona which causes the O2 bond
to split, freeing two (O1) atoms which then collide with other (O2) molecules
to create ozone. CD systems generally produce about 3-5 times more concentrate
than UV units.
What does Ozone
do? Ozone is the most powerful oxidizer and disinfectant that can be used
safely to purify air and water. In fact, it is one of the most powerful
alternatives to chemical sanitation. Compared to chlorine, the most common
water disinfection chemical, ozone is a more than 50% stronger oxidizer and
acts over 3,000 times faster. Any pathogen or contaminant that can be
disinfected, altered or removed via an oxidation process will be affected by
ozone. Ozone has been scientifically proven as an affective broad-spectrum
antimicrobial agent in deactivating bacteria, viruses, molds, spores, cysts,
yeast, mildew and fungi. Ozone oxidizes iron, sulphur, manganese, hydrogen
sulfate, and eliminates oils and other contaminants in the water.
This is why
ozone is used by water bottling plants, is used to clean waste water and toxic
waste, is used to purify air in hotel rooms and why all Olympic Games
Competition Pools have been purified by ozone since 1984. Ozone is pH neural
and will not adversely affectthe pH.
Does a swimming
pool or spa still need chemicals with ozone? The answer is yes. Ozone will
handle the bulk of sanitising requirements. However, due to the short life of
ozone, a small amount of sanitiser will be required to provide a residual in
the water. Because residual levels are so low there is no detectable taste or
odour. Normal residual levels are around 0.5ppm to 1ppm, thus reducing normal
chemical usage by up to 90%. Ozone also works with mineral systems and salt
chlorinators and reduces their consumable consumption.
Other methods
There are a
variety of other methods including ionisation, electrolysis and mineral
systems, which operate either alone or in combination with chemical sanitisers.
The trace-element system Nature2, for example, claims to reduce the need for
chlorine to just 0.5ppm. Anti Bio technology uses low frequency sound waves and
electromagnetic fi elds to assist in the removal of impurities from water and
to reduce the amount of chemicals required. The Aquabrite System is an
environmentally friendly, simple, efficacious non-chlorine disinfection system
that has been tried and proven for more than 14 years. It uses the natural
disinfection qualities of copper and silver, through electrolysis, with a
proprietary oxidising agent
known as Aquabrite. The synergistic effect of the copper and silver ions and
the oxidising agent disinfects the pool and spa water without creating
irritants.
Is magnesium chloride the new salt?
Poolrite has
launched a new product called Magna Blu, which is designed to work with their
crushed glass Diamond Kleen filter media to form the Magna Pool System. The big
difference between Magna Blu and existing salt chlorinators is that, rather
than using sodium chloride to effect sanitisation, it uses other salts, in
particular magnesium chloride and potassium chloride. Poolrite says this makes
the water healthier, and importantly makes the water recyclable – as the sodium
levels are a current impediment to using backwashed water for other purposes,
such as watering gardens. Poolrite believes this backwashed water could even be
diverted and used to flush household toilets – saving mains water which is
currently used for that task.
New high-tech
electrode could revolutionise sanitisation
Alan Lewis, pool
consultant from Aquazure, explains a new Swiss electrochemical technology which
could have far reaching effects in the pool industry
In 1994 when
Philip Barlow was technical director of Watertec Engineering in Brisbane, he produced a
publication extolling the virtues of ozone as a disinfectant in swimming pools.
In the opening paragraphs he compared the oxidising potential of various
oxidising reagents in the following interesting table:
Oxidising Reagent . . . . .
. . . . . . . . . . . . . . . . . .Oxidising Potential (V)
Fluorine . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.06
Hydroxyl free radicals . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.80
Atomic Oxygen . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.42
Ozone . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.07
Permanganate . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67
Hypobromous acid . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.59
Chlorine dioxide . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.50
Hypochlorous acid . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.49
Chlorine . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.36
Oxygen . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.23
Bromine . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.09
Hypochlorite . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.94
Note that hydroxyl free
radicals are second highest on the table – even higher than ozone.
Barlow’s comment was that
“with a short life of microseconds they do not play a major part in achieving
disinfection”. In fact, ozone does have a longer life in water than hydroxyl
free radicals. However, if we compare continuous production of both reagents in
a slip stream of the pool circulation, surely we could then say that the former
will be more effective than the later. This is where the DiaCell has brought a
new dimension to the challenge of disinfection. How? Because it has been made
possible by the development of a very special electrode, and unlike ozone it
also makes hypochlorite
which can survive in the pool as long as the electrolysis continues to generate
the disinfectants. The Boron Doped Diamond (BDD) electrode is produced in a
similar fashion to the production of artificial diamonds in a process called
Chemical Vapour Deposition (CVD), in which it deposits a thin film of
polycrystalline diamond on a substrate of silicon. The crystals are formed from
raw graphite under high temperature and pressures. The result is a highly
efficient electrode which can generate a powerful mix of chlorine; peroxydisulphate;
peroxydicarboate; ozone; hydrogen peroxide; and other hydroxyl radicals,
simultaneously in the electrolytic cell. Those chemical species with longer life are continuously
swept into the pool by the slip stream until a steady state of Free Chlorine
residual is created.
Once the initial dose of
salt(s) has been introduced to the pool to a maximum residual of 1000ppm (or
mg/L) – there is no further need to add chemicals with the exception of
occasional replenishment of salt lost to splash or backwash. The doped diamond
has excellent stability under varying pH and temperature and in the presence of
other aggressive chemicals. Low fouling is sustained by phased reversal of the
polarity on the electrodes. Compared with other electrodes the BDD has a much
greater potential (> 4 volts) resulting in a faster inactivation of the
pathogens in the water. The net result of this system is dreamlike for
operators with minimum handling of chemicals; low running costs and very low
maintenance of the equipment.
The design of the cell is
versatile and can be assembled in various combinations so as to ensure the
minimum residuals required by the local health authorities. After three years
of trials, the DiaCell has now been approved for use in public pools by the Swiss
Health Department and will shortly receive similar accreditation from the
French health authorities. Neither should it present a problem for health
authorities in any of Australia’s
states and territories, because of the fl exibility in design and assembly. The
DiaCell removes the need for chemicals and makes the water easier to recycle. It
will be particularly appropriate for remote areas where transport of chemicals
presents a prohibitive factor in running pools in outback areas with small
populations. There are no storage or OH&S problems of any substance
relating to handling of chemicals, and no concentrations of
disinfectants likely to present issues of corrosion in plant or the pool and
its surrounds, because of the low residuals involved in the processes.
The DiaCell described here
applies primarily to large commercial pools, but Adamant Technologies also has
a domestic product using the same technology called the Oxineo. For more
information email Alan Lewis on aquazure@bigpond.net.au
Extract from December 2006/January 2007 edition of SPLASH
pool & spa industry magazine
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