Rethinking pools to boost safety and minimise use of water, energy and chemicals

white paper THE RETHINK WATER NETWORK | RECREATIONAL WATER | MAY 2014 Rethinking pools to boost safety and minimise use of water, energy and chemical...
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Rethinking pools to boost safety and minimise use of water, energy and chemicals Safe pool solutions ensuring high water quality and minimised use of resources

Rethinking pools to boost safety and minimise use of water, energy and chemicals Safe pool solutions ensuring high water quality and minimised use of resources Version 1.0

About this white paper This white paper was developed by the Rethink Water network in Denmark. The work is coordinated by the Danish Water Forum. The Rethink Water network consists of more than 60 technology and consulting companies, water utilities, water organisations and public authorities. It was established to support our partners internationally in developing the highest quality water solutions. Quoting this white paper Please quote this white paper and its articles: “Kristensen, G.H. (Tech. Ed.) & Klee, P. ( C.), 2014. Rethinking pools to boost safety and minimise use of water, energy and chemicals. Safe pool solutions ensuring high water quality and minimised use of resources. The Rethink Water network and Danish Water Forum White Papers, Copenhagen. Available at”

Editor in Chief Pia Klee, kickstarter for the Rethink Water platform [email protected] Technical Editor DHI Gert Holm Kristensen [email protected] DHI Morten Møller Klausen [email protected]

Contributors COWI Torben Schack [email protected] Danish Rootzone Technology Jørgen Løgstrup [email protected] DHI Gert Holm Kristensen [email protected] DHI Morten Møller Klausen [email protected] inBlue Ole Grønborg [email protected] LiqTech Daniel Larsen [email protected] Rambøll Henning Hammerich [email protected]

Language Editor David Lalley, WordDesign

© The Rethink Water Network & Danish Water Forum 2014

Executive summary Walking through the glass door separating our old and our new facility you feel the huge difference between the new and the classic pool system. It really stresses the need for public pools to bring down the level of clearly harmful chlorine by-products

Even if the practical and legal requirements

a day, which is much better than traditional

with regard to the operation of public pools and

systems that only remove pollution a few times

water parks vary widely on a global scale, most

a week, or even less. This filtration is typically

of the technologies used have hardly changed

combined with other technologies to remove

in the last 100 years. For over a century, chlorine

the remaining particles.

Improved water treatment

energy consumption. However, this is not good


The mechanisms controlling the formation of

for the health of those using these pools.

First to embrace new concept, Sweden In Sweden, the Filborna Arena in Helsingborg was the first public swimming facility to embrace new technology concepts that avoid harmful chlorine by-products and thereby improve the indoor environment for swimmers. In 2010, new extended pool facilities, built as a greenfield project, were added to the existing facility. A radically different water treatment concept, combined with an innovative air ventilation­ system, has reduced the level of chlorine­ by-products­to detection limits, pro­ tecting­ people from an intense chlorine odour, itching of the eyes and skin, and respiratory ailments. In addition, the use of water, energy and chemicals were greatly reduced compared to the traditional facility, which is separated from the new by a glass door. In 2012 the Filborna Arena was the proud host of the Swedish swimming championships. (Courtesy: inBlue)

has been the preferred dis­infectant for making sure the water is free of unhealthy bacteria and

Improved ventilation

– due to the lack of alter­­natives – the continued

Much of the remaining by-products are then

use of chlorine is still the most realistic future

removed with a gas stripper, UV technology and

scenario. Yet large quan­tities are not always

other equipment. The chlorinated com­pounds

needed to keep the water safe, and lowering

are also removed at the surface of the pool by

the chlorine content im­proves the water and

new kinds of ventilation. Nowadays most venti-

air, protecting people from the intense chlorine

lation systems in swimming pools are designed

odour and itchy eyes and skin.

to keep the air over the water surface still, in order to cut down evaporation and thus reduce

harm­ ful chlorinated disinfection by-products are very complex and still poorly understood,

Improved overall resource efficiency

but there is a general consensus that the forma-

Another important perspective on the grow-

tion rate increases with higher concentrations

ing pool market is the trends towards larger,

of chlorine. One option, therefore, is to lower

advanced pools that in turn lead to an increased

the pH of the water – a measure that some

use of water, energy and chemicals. The risk

coun­ tries have practised for years. Chlorine

is that operating costs rapidly escalate. There

occurs in a much more active form at a lower pH,

are, of course, physical limits for how efficient a

which means that the same disinfection effect

very resource-intensive facility like a swimming

can be achieved with a lower chlorine content.

pool can become, but the opportunity to bring

Another option is to redesign water treatment

down the consumption of water, chemicals and

systems to remove solid impurities more often

energy is certainly available. This white paper

in order to avoid the chemical breakdown of

provides numerous examples of how owners of

contaminants with chlorine. An optimised water

public pools have reduced their operating costs

flow and drum filters will remove 90 to 95 per

and at the same time achieved a more healthy

cent of solid organic substances up to 200 times


WHITE PAPER - RECREATIONAL WATER | 4 Photo: Kontraframe/City of Copenhagen


In control of wastewater to protect people and ecosystems Efficient solutions for treatment of wastewater

Harbour pool in central Copenhagen, Denmark In natural water environments as rivers, lakes and the sea, the quantities­and flow of water are normally huge, and bacteria that are part of a natural balance break down contaminants­resulting­from people bathing. As a rather unique story, the harbour of Copenhagen has been transformed­from an industrial port to a vibrant cultural and social centre of the city in just a decade. People now swim and enjoy water playgrounds in the city centre in an impressive natural outdoor pool – the harbour itself. The industrial water traffic is gone, so modernising the sewer system and diverting local rainwater improved the water quality so the City of Copenhagen­was able to open this public harbour bath in 2002. Protection against wastewater discharges during heavy rainfall is managed by integrated wastewater strategies and innovative technology. An integrated­bathing water quality forecasting system measures sewer overflows, and hydrodynamic and bacterial models simulate the water quality in the harbour. This system provides real-time information about whether or not the water quality complies with the EU Bathing Water Directive. Download the white paper on wastewater treatment­, which is part of the same series as this white paper on



A technology shift for better health and higher efficiency



Balancing safe water with a healthy pool environment



The full opportunities with an optimised design build from scratch



Upgrading of existing facilities to cut costs and improve water/air



Documenting performance of new water treatment technology



Design of water environments with no use of chemicals


If your goal is water efficiency, Denmark is ready as a partner



Outdoor pool World Expo 2010, China Many architects and designers are attracted and inspired by water and natural water environments. This was also the case when Denmark’s pavilion for the World Expo 2010 in Shanghai was designed by the award-winning Danish architectural firm BIG (Bjarke Ingels Group), and the Little Mermaid statue of Copenhagen was brought on a historic trip to China. The bronze-skinned statue has sat pensively on the edge of the harbour since 1913, created to commemorate the leading character in the 19th-century fairy tale The Little Mermaid by Danish author Hans Christian Andersen. It was brought to the World Expo 2010 as a token of China–Denmark friendship and as a symbol for the unique story of Copenhagen Harbour’s clean water, as explained on the previous page in this white paper. The pavilion was built around an artificial pond whose water represented the sea surrounding the statue at home in Copenhagen harbour. The water was kept clean and safe to take a swim in, using the same technology concept introduced in this white paper. (Courtesy: BIG and inBlue)


1. A technology shift for better health and higher efficiency Having worked most of my life in the facility, it is amazing to see this dramatic change in water and indoor air quality. Changing our Olympic-size pool to a family swimming centre with more pools was a complex project, since all the new equipment had to fit into the existing basement, but we were able to double the water treatment­capacity and still keep water and energy consumption the same

Recreational water facilities are popping up

water and energy rise, the risk is that operating

everywhere in the world, with fun and exotic

costs will go through the roof.


Technology shift in pool water treatment The mechanisms controlling the formation of harmful chlorinated disinfection by-products are very complex and still poorly understood, but there is a general consensus that the for­ma­tion rate increases with higher concen­ trations of chlorine. By removing solid organic conta­mi­nants from the pool water before they dissolve and are broken down by chlorine, the the water quality and indoor air will be considerably­improved and less chlorine is needed. The photo shows a sample of particles, mainly skin cells, collected by a drum filter up to 200 times per day. Imagine how these, if not passed to the sewer as waste, will react inside a sand filter. With hot chlorinated water stressing these particles for 7 days or more the skin cells will be dissolved and then return to the pool creating lots of unnecessary chlorine by-products that swimmers and bathing guests then will inhale. (Courtesy: inBlue)

water environments featuring pools, water slides, river rides, wave surfing, spa relaxation

Attention of politicians important

and so on. These facilities extend from public

Another argument for a technology shift lies

swimming pools for local citizens to major

in the much healthier pool environments. Yet,

waterparks as tourism destinations. Even if the

the pool environment will probably not be a

practical and legal requirements for operat-

big selling­point for most investors even if the

ing public swimming pools vary considerably

many public swimming pools and water parks

throughout the world, most of the technologies

need to distinguish themselves from the many

used in these facilities have hardly changed in

com­pe­titors that will be out there. The market

the last 100 years, no matter where the facility

is highly conservative and competitive, which

is located,. The technologies most commonly

means that the adoption of new technology

used for are sand filtration, activated carbon

concepts requires solid documentation for their

and chlorination, adapted from the purification

economic validity. Attention from politicians

of drinking water.

and public authorities should then help push the pool market towards healthier and greener

Increased resource efficiency

solutions based on relatively strict legislation,

One argument for a technology shift lies in the

which then creates a demand for innovation

potential for reducing the consumption of water,

in the supply chain. In Denmark, the political

energy and chemicals in a resource-intensive

term “innovation promoting legislation” has

sector like swimming pool operations. Reduced

already caught the attention of politicians as

consumption will play an increasingly important

new Danish legislation (Number 623) for pools

role in being able to follow the global trend

strictly limits chlorine by-products and guides

towards larger and more advanced recreational

pool owners towards reducing both pH and free

water environments with more visitors, higher

chlorine. It also requires automated measure-

temperatures and other features that make a

ment of key parameters combined with daily

facility even more resource-intensive. If the

manual measurements by staff and frequent

costs of increasingly scarce resources such as

monitoring checks by an accredited laboratory.


2. Balancing safe water with a healthy pool environment Lowering a pool’s chlorine concentration is a three-step concept. First, the water flow is optimised to remove organic contaminants in a mechanical instead of a chemical process. Secondly, the pH is lowered to make the chlorine more active and thirdly the ventilation­ flow is designed to remove chlorine by-products­from the water surface GERT HOLM KRISTENSEN Head of Innovation DHI

Spending time in water is fun and gives numer-

the steep rise in childhood asthma observed

ous health benefits, but the moist, chlorine-

over the past decades. In Germany, parents

scented air is often part of the experience. For

are therefore now advised to refrain from

over a century, chlorine has been the preferred

baby swimming with children aged 0–2 years

disinfectant to ensure the water is free of

if allergies­often occur in their family. Another

unhealthy bacteria and – due to the lack of

important sign of problems with chlorine is the

alternatives – the continued use of chlorine is

health of elite swimmers. Even though they

still the most realistic future scenario. However,

live a more healthy life than ordinary people,

large quantities of chlorine are not always

research shows that they are diagnosed with

needed to keep the water safe and free of

asthma or asthma-like symptoms nearly twice

bacteria, and lowering the chlorine content

as often. So even if all elite athletes have an

protects people from the intense chlorine odour

increased risk of asthma, regardless of the type

and itching of the eyes and skin.

of exercise taken, research has shown that elite swimmers have a 50 per cent greater risk of

Chlorine has negative health impacts

asthma than tennis players, for instance.

When chlorine reacts with organic and inorganic matter like sweat, saliva, urine and skin resi-

Harmful by-products hanging in the air

dues released from people, it forms disinfection

The air in swimming pools may be the cause,

by-products (DBP) that either remain in the

as swimmers are often exposed to high levels

water or evaporate into the air. The chlorine

of trichloramines, which are by-products

itself does not smell – the smell stems from

formed when chlorine breaks down organic

the by-products formed when the chlorine

materials. Trichloramine has a damaging effect

breaks down the impurities. Unfortunately,

on the lungs, and Scandinavian researchers

a great deal of studies support that these

suggest that this may be one of the causes of

chlorinated by-products – especially chloroform

the increased incidence of asthma for elite

and chloramines – are more harmful than

swimmers­— The World Health Organization­

previously believed. The hypothesis laid down

WHO set a trichloramine limit of 500 micro-

by some researchers is even that the chlorine

grams per cubic metre, as any higher level gives

compounds contaminating the air of indoor

the risk of acute injuries, but the researchers

swimming pools are at least a partial cause of

measured­levels that are 8–10 times this figure.

Saline pools, Denmark Saltwater treatment is known to relieve certain types of skin diseases and is also known to have a natural disinfecting effect. These features are used in a very unique wellness centre on the island of Læsø, which is a former church converted into this modern wellness centre, supported by architects and engineers. In this part of Denmark, the highly saline groundwater concentrations have been mined since the Middle Ages and are a landmark of the island. This water is now used for the highly saline pools with concentrations of 30 per cent salt. However, the use of dissolved salt as an alternative to chlorine is not allowed by the current Danish legislation, but the facility has been able to get dispensation to operate the pools at a lower chlorine concentration than required by this legislation. (Courtesy: COWI)


Heated indoor pool in hospital, Australia Recreational use of water can deliver important benefits to health and wellbeing. Yet, there may also be adverse health effects associated with recreational use if the levels of chlorine by-products in the water and air is too high. This is why the Hyrondelle private hospital in Sydney in Australia decided to opt for a new technology concept in its heated indoor pool. The pool is part of the hospital’s hydrotherapy facilities, which are used for graduated exercising and treatment and allow physiotherapists to target specific muscle groups effectively, because warm water and buoyancy assist movement and encourage pain relief. (Courtesy: inBlue and Aquazure)

Changing air ventilation streams

Changing water treatment systems

Higher disinfection effect with lower pH

Most ventilation systems in swimming pools are

Another way to improve pool environments

Another issue is to lower the pH of the pool

designed to keep the air over the water surface

is by redesigning water treatment systems. A

water, which countries such as Germany and

still, in order to cut down evaporation and thus

new technology concept has proved it possible

Austria have practised for years. Chlorine occurs

reduce energy consumption. As a result, one

to improve the water quality and at the same

in a much more active form at a lower pH, which

way to improve the indoor environment is

time reduce the use of chlorine. The key is to

means that the same disinfection effect can

to redesign the air flow for faster removal of

remove solid impurities to avoid the chemical

be achieved with a lower chlorine content.

chlorine by-products. Scientific studies of the

breakdown by chlorine. An optimised water

Lowering the pH to the recommended level of

three-dimensional air flows in swimming pools

flow removes the organic matter as fast as

6.5–7.0 makes it necessary to add a little more

have led to the development of a new design

possible, with drum filters removing 90–95 per

of the hydrochloric acid that is normally added.

of the ventilation systems that draw away the

cent of solid organic substances­up to 200 times

Further improvement of the water environ-

air just above the water surface. This reduces

a day (test by NSF, the Public Health and Safety

ment might be possible, either through direct

not only the swimmers’ exposure to potentially

Organization in USA). This is much better than

removal of chlorine by-products from the water

harmful chlorine by-products, but also signifi-

traditional systems­that only remove pollution

or by removal of the so-called precursors for

cantly improves the indoor air environment of

a few times a week or even less. This rapid

by-product formation – for instance by avoiding

the entire pool facility, which benefits the staff.

removal will maintain a lower chlorine concen-

accumulation of particulate organic matters in

However, changing existing ventilation systems

tration because the chlorine no longer has to

the filters of the water system.

into the new design is often difficult.

degrade the organic materials.


State-of-the-art aquapark, Sweden Around fifty swimming pools have so far embraced the new standardised concept and the new Hyllie Waterpark currently under construction in Malmö in Sweden is one of them. When opening in 2015, the facility will be among the largest water parks in Scandinavia, with seven water treatment systems based on the new concept operating in the basement. This state-of-the-art facility will feature an indoor environment that is free of chlorine by-products and probably the most energy and water-efficient water park in the world. If compared to conventional systems in Sweden, the consumption of water and energy is reduced to just half. The facility is just 25 kilometres from Copenhagen, making it an attractive excursion destination for Danes. too. (Courtesy: inBlue)


3. The full opportunities with an optimised design build from scratch We started working with scientists 10 years ago to rethink water treatment and ventilation of public swimming pools. Three years later, our first full working pool was in place reducing the use of chlorine by up to 80 per cent. New facilities, like the new Hyllie water park in Sweden, are the final result of optimising design and construction in over 50 projects. This will be the ultimate experience, with the lowest possible utility costs

A collaboration involving scientists­, owners of

such as skin cells, urine, sweat, cosmetics and

public swimming pools, a technology provider

other impurities. If they are efficiently removed,

and a research institute has resulted in the

the chlorine compounds in the air above the

entire water treatment and ventilation concept

basins are almost eliminated, and, in addition,

of public swimming pools being rethought and

much less chlorine is needed for disinfection.


Flow modelling The circulation of water must be optimised to remove the impurities as swiftly as possible. Flow modelling has three advantages over using standard construction design with standard fittings. 1. Particles are quickly transported to the cleaning system before dissolving 2. Treated water returns can be designed with a 90 per cent reduced head loss compared to standard returns, contributing to the overall reduced energy consumption. 3. Chlorine distribution is aligned perfectly with each unique pool design. The CFD model illustrated is from the design of the pool with the Little Mermaid in section one. (Courtesy: inBlue)

optimised into a standardised concept. This rethinking extends from the way in which the

The new concept

contaminated water circulates in the pool over

The new concept is divided into three steps.

the many water filtration steps to the design

Firstly, 3D computer modelling is used to

of the air ventilation set-up. More than 50

improve the circulation of water in the pool in

public pools in Denmark, Sweden, Australia and

order to remove the impurities as swiftly as pos-

Germany have implemented the concept so far

sible. Secondly, the filter system is completely

– many as greenfield projects, which gives the

altered. In the usual sand filters, chlorinated by-

advantage of implementing the full concept.

products are constantly generated when warm chlorinated water dissolves the impurities

Radical thinking

captured by the filter over a period of a week

The optimised water treatment and ventilation

or two. With the new filter system, a drum filter

set-up is a radical new concept, and there is

equipped with a filter screen makes sure 90–95

almost none of the traditional equipment in the

per cent of the impurities released from the

technical spaces. The investment is the same as

bathers are washed to the sewer within hours.

for a conventional high-quality system and the

To remove the last 5–10 per cent of particles,

financial gains are certainly there as the use of

the drum filtration is normally combined with

water and energy are halved compared to the

part-flow flocculant-enhanced sand filtration.

most ideal design using classic technology such

Many of the chlorine by-products are removed

as sand or DE-filter based systems. When start-

with an air stripper, UV technology and other

ing out in the development phase, the scientists

equipment. Thirdly, new innovatie ventilation

adopted a big-picture perspective by consider-

principles are used to deal with any remaining

ing the origins of the contaminants. Avoiding

volatile chlorinated compounds at the water

these contaminants is impossible, but would

surface of the pool.

it be possible to avoid the harmful substances resulting from chlorine breaking down such

Using gravity instead of pumping

contaminants? This led to the basic idea that

The ideal way to achieve the lowest pos-

chlorine is only used to ensure that people do

sible operating costs, and the safest and

not infect each other, not to break down waste

most healthy environment, is when the water


Reducing energy consumption by 25 percent, Denmark The ideal way to ensure the best possible environment and lowest possible consumption of energy, water and chemicals is to design the system on a green-field basis, fully integrated with the overall design of the building. This was the opportunity open to the Valby Water Culture Centre, owned by the City of Copenhagen, which was built from greenfield. The building challenges the visitor’s senses with its irregular angles and inclined walls. From a water playground, the visitor enters a water world with entertaining water staircases, water tunnels, counter-current canals, caves, a large wellness area with hot water basins, etc. Working together, the technical consultant and architects were able to create a pool facility that uses 25 per cent less energy compared to other Danish public swimming pools using classic technology. (Courtesy: Rambøll)


Upgrading of existing facilities, Denmark When Greve Swim Centre was renovated, the new water treatment concept was imple­mented­ to provide a more healthy indoor environment­. The renovation project has turned this classic­ facility with an Olympic-size pool into a family centre with several pools instead. The project was a complex project because all new equipment­had to fit into the existing basement­, but it has paid off as the post-renovation water and energy consumption is on the same level as the old system, while the capacity of the water treatment system for the new – higher loaded – pools has been doubled, in accordance with the Danish national regulations. (Courtesy: inBlue)

All our students swim at school, and many of our elite swimmers had respiratory problems. We therefore chose to be part of a threeyear research project and are now very proud to be able to tell new students­ that we offer them the most healthy pool in Denmark

treatment system is an integrated part of the

of energy is consumed by the pool sector, so

building’s design and as much water as possible

increasing­the energy efficiency should be

flows by gravity rather than by pumping. In a

a priority. In many countries, the incentives

building designed for best effect, it is possible

to reduce energy consumption are big, and

to achieve a total headloss, of less than one

in Denmark­, which has some of the highest

metre (3 feet) through the entire system,

energy rates in the world, the need to reduce

from pool surface through equipment in the

energy consumption has fuelled architects

basement and back through the treated water

and engineers­to come up with a variety of

return. A traditional sand or DE-filter system

innovative many interesting projects. Besides

needs at least 10 metres (30 feet) of head, or 10

minimising the evaporation from the pools,

times more. Dramatic­reductions in energy use

efficient heat recovery from ventilation systems

will be needed to meet forthcoming demands

is important as is optimising the buildings for

for reduced environmental impacts and sustain-

the use of both active and passive solar heating.

ability of swimming pools and water parks.

Energy consumption for lighting system can be

Energy-efficient buildings

A design with a more natural ventilation during


Besides an energy-efficient design of technical

the summer months saves heat and electricity

installations for ventilation and water treat-

for ventilation systems. Also heat recovery

ment, it is important to have energy-efficient

through heat exchangers for transfer of heat

swimming pool buildings. Designing everything­

from used shower water to heating the new

from scratch is an interesting challenge and

shower water is a common feature in public

important opportunity for innovation. A lot

pools and water parks.

Elite swimmers dropping asthma medicine The first development stage of the concept of improved water treatment and air ventilation was carried out at the Bernstorffsminde Private Continuation School in Denmark. The school serves young people as well as young elite swimmers. When the development project was kicked off, six of the 20 swimmers attending the school had asthma, but shortly after the new concept was implemented all of them stopped using asthma medication. This was also the case at other public pools with elite swimmers, which have also reported swimmers being able to dispense with their asthma medication. The photo shows Sabine Devantier Christensen explaining in Danish national news how her asthma problems disappeared when training for competitions in the Bernstorffsminde pool.

greatly reduced by using the latest LED fixtures.

WHITE PAPER - RECREATIONAL WATER | 8 Solving challenges expanding outdoor facilities, Denmark The tropical holiday and activity centre Lalandia located in the southern part of Denmark faced a set of challenges when expanding its outdoor facilities, as the load is extremely heavy in warm and sunny holiday seasons. The extension included a new children’s pool, a large spa pool and a new water slide able to handle 2,600 people per hour, corresponding to 20 times the capacity of the traditional water slide. Water treatment must always be dimensioned to a pool’s maximum bathing load and installing a drum filter before conventional sand filters proved to be a solution able to handle this intense load. In addition­, 3,000 tons of water (800,000 US gallons) were saved as the backwash water of both membrane filters and sand filters is regenerated and reused for the basins as well as for backwash of the sand filters. (Courtesy: Rambøll)


4. Upgrading of existing facilities to cut costs and improve water/air There are physical limits for how efficient you can be when renovating a very resource-intensive facility like a swimming pool, but the opportunity to bring down the consumption of water, chemicals and energy is certainly there HENNING HAMMERICH Senior Consultant RAMBØLL

The market for swimming pools and water parks

in water consumption might play a bigger role

is trending towards larger, more advanced pools

then as they are much more significant. Rede-

with higher temperatures and more resource-

signing water treatment systems typically give

intensive features, leading to an increased use

50-60 per cent savings in water consumption

of water, energy and chemicals. This involves

compared to traditional systems. These are for

a risk that operating costs go through the roof

instance achieved by reusing the regenerated

when energy and water prices are not stable.

backwash water from the sand filters. A differ-

However, investing in increased capacity goes

ent and more radical step in the renovation pro-

hand in hand with a more resource-efficient

cess would be to swap most of the sand filters­

system design. The potential to improve pool

for water- and energy-saving drum filters. Such

environments and at the same time reduce the

a solution might save more than 50 per cent in

use of resources certainly also exists for existing­

water consumption.

pools. The best time to look into this is when an overall renovation is coming up. The limited

Significant savings in energy consumption

space available for technical installations in

Upgrading water treatment systems also leads

current facilities is rarely a limitation, because

to energy savings. Typically 20-30 percent

modular and highly engineered designs make it

savings in electricity consumption and 15-20

easy to fit new technology elements into space-

percent savings in heat consumption can be

constrained facilities.

achieved. Savings might also be found by replacing old recirculation pumps with mordern

Reduced use of chlorine and water

energy-efficient pumps. This can be combined

Besides ensuring much fewer harmful chlorine

with redesign and replacement of the piping,

by-products, a shift to new techno­logy provides

Upgrading public swimming pool, Denmark When the public swim centre in Køge was renovated and upgraded to a new capacity of 300,000 visitors per year, it involved renovation of the roof, steel structures, ventilation, plumbing, electrical systems and a new water treatment system. The water flow within the existing technical areas was increased by almost 60 per cent, thereby improving the water quality in the pools, baby pool and hot tub. This technical solution includes drum filters, which remove larger particles, and polymer membrane filters for removing the fine particles that make up 10–15 per cent of the organic mass. Regenerated water is reused for priming and backwashing the membrane system. The total savings achieved are a reduction of energy consumption by 20 per cent and water consumption by 55 per cent. (Courtesy: Rambøll)

aiming towards reduced headloss for the large

up to 30 per cent savings in chlorine. This may

recirculation flows and with new intelligent

not make a great difference in the overall cost

control of the recirculation flow adapting to the

picture, but for most operators it is still a benefit

actual number of pool users, and operating with

to reduce chlorine consumption. The savings

a reduced flow during the night.

WHITE PAPER - RECREATIONAL WATER | 10 Photo courtesy:: Danish Arthritis Society

Online monitoring reveals potential for system optimisation Detailed online monitoring­of water quality has helped the public swimming centre in Gladsaxe, Denmark reduce its electricity­consumption for pumping by 40 per cent, because the water flow is now automatically­adjusted according to the numbers of pool users. In addition, the online monitoring has been used to test and comprehensively document four different UV-based technologies­for reducing the level of combined chlorine. The efficiency of the technologies as well as the financial picture involved in installation and operation were then evaluated on the basis of these results. The test proved that using these technologies to their full potential is possible­when combined with on-line monitoring of combined chlorine, as they can be operated­in energy-saving mode. (Courtesy: DHI)


5. Documenting performance of new water treatment technology To push technology change, the performance testing and documentation of new water treatment technology should include solid data for the response of the entire pool system. We have documented huge temporal variations in water quality using advanced online monitoring techniques MORTEN MØLLER KLAUSEN Senior Process Research Engineer DHI

Positive health effects and an increased

technology, combined with comprehensive

need for resource efficiency in recreational


facilities can push the pool and water park

not only help to fine-tune the technology. It

markets towards new water quality standards.

also provides an important support in setting

However, any radically change of basic water

new standards for water quality and water

treatment concepts is indeed a challenge

treatment­systems in swimming pools.



because in most places the pool market is both highly conservative­and very competitive. Solid

Testing response of the entire system

documentation­for the performance of new

Temporal variations in water quality parameters­

water treatment technology is therefore crucial

make the testing and documentation of tech­ for a market breakthrough, since investors­ nology performance difficult. This is due to are normally positive with regard to using the complex interaction between bather load, technology­suppliers as a source of information.

chlorine reaction chemistry, circulation and treatment of water, which together govern

Supporting market breakthroughs

the water quality in recirculated pool systems.

Pool facilities are often operated in accordance

This complexity makes it insufficient to test

with relevant national legislation, and this is


the market situation that technology suppliers

the efficiency of the addition or removal of

have to address. The day-to-day checking of

specific components. The testing must include

water quality is a low-frequent grab sampling

a monitoring of the response of the entire

and analysis, and online data from the plant

pool system, which is further complicated

control system is not used to check and optimise­

because the water quality parameters are low

the pool system. This means pool owners

in concentration and difficult to measure. This

and technical­staff do not normally have any

then means the testing­and documenting of

extensive­knowledge and understanding about

new water treatment technology requires that

the workings of their systems. They often

comprehensive in-depth monitoring of water

only rely on documentation from technology

quality is conducted using both frequent off-

suppliers­ . As a result, a supplier’s in-depth

line measurements as well as online monitoring

know­ ledge of the underlying fundamental

of the most relevant parameters.

physico-­chemical mode of action of a particular

New filter technology saving water For the new public swim centre in Randers in Denmark, investment in new filter technology was good business. The centre’s hot water pools and a 50-metre Olympic pool will be kept clean with a new filter technology called ceramic membrane filtration in the six water treatment systems. This technology replaces the classic sand filters. For this facility, flushing these sand filters would have required up to 100 cubic metres of water per week. Instead, the ceramic filters fitted with a membrane made of silicium carbide are automatically cleaned with air and just a small amount of fresh water. This reduces the water consumption by as much as 90 per cent, which for a large Danish facility like this amounts to annual savings of 30,000 euros. (Courtesy: Provital Solutions and Liqtech)








THM reduced when chlorine is reduced Trihalomethanes (THM) are unwanted volatile components formed in pool water as a result of the reactions between the chlorine and the pollution caused by the bathers. The figure shows the impact on THM formation at two different chlorine concentrations in a warm pool. At the low chlorine level of 0.4 mg/litre, the THM in the pool water is around 20 µl/litre while at the higher chlorine level of 1.5 mg/litre the THM level is 40–50 µl/litre. This leads to the conclusions that pools should be operated at the very lowest level of chlorine possible, just ensuring the hygienic quality of the pool water. (Courtesy: DHI)

Huge variations in water quality over time

water quality. In addition, a better insight into

the pool water quality and operations. A

Research in pool water chemistry over the

the parameters of importance to the pool water

better understanding of the link between

last decade using advanced online monitoring

quality has shown that the traditional direct

the dynamics­of the water quality with the

techniques has shown that the concentrations­

coupling between the circulation of pool water

variations­in treatment plant and system

of disinfection­by-products and related water

for chlorine distribution and the treatment­ operation­as well as bather load is needed,

quality­parameters are highly variable both

for maintaining the pool water quality­is

and can be accomplished with comprehensive

within a single hour and from day to day.



monitoring. This monitoring­should include

Observed by-products are trihalomethanes

the actual processes taking place in the pool

using online monitoring­and frequent off-line

(THM) and combined chlorine, which are

water will therefore open up new possibilities

measurements and registrations of bather load,

both regulated normally, and water quality

for optimised­technology/system design with

thus establishing the data required for system

parameters­dissolved organic carbon (DOC).

reduced energy consumption combined with

analysis and documentation. Based on such

Observations have clearly shown that plant

improved water quality.

data, improvement options can be identified



and prioritised based on their cost and ease

operation – as well as the interpretation of experimental results – may be misleading

Potential improvements in pool operations

of implementation. The effect is normally­

and unable to show correlations between the

Many facilities therefore have unexploited


performance of processes/technologies and

potential with regard to significantly improving­


Huge variations in pool water quality Many pool facilities have unexploited potential for significantly improving both the water quality­ and pool treatment operations through a better understanding of how the dynamics of the water quality interact with variations in treatment plant concept, system operation and bathing load. The figure illustrates the daily and day-to-day monitoring in trihalomethane concentrations in a warm water pool measured during technology assessments using advanced online monitoring technology. (Courtesy: DHI)





Water playground used in all seasons, Denmark Water is often used to enhance the urban environment and this is also the overall idea for a new water-activity playground in one of the parks in central Copenhagen, the capital of Denmark. In this playground the universal story of water is paired with the story of the city for children and youngsters to get a playful and natural understanding of water and how it plays a key role in day-to-day life, both in history and in the present day. They get a unique opportunity­to combine play and exercise, and also cool off in the hot summer months. It is built as a city and shows the water flowing from clouds via the city’s rivers and sewers and into the ocean. While some activities run automatically, other activities require physical activity to work. The playground works both with and without water, and will therefore also be used as an ordinary playground outside the summer season. The water used is – for health reasons – clean drinking water delivered by the city’s water supply and the plant is emptied every day after use. (Courtesy: Force4 Architects)


6. Design of water environments with no use of chemicals For recreational water facilities designed without

In many cities, recreational water is an

it is still important to ensure the water is of a

increasingly important element of the city’s

sufficient quality and safe, not placing people’s

development, in urban planning and in land-

health at risk.

chlorine disinfection, it is essential to always carry

scaping. The inhabitants in urban areas often value water highly and in many different ways

Designing safe solutions

because it influences – for instance – local

Ensuring and checking the water quality should

out a proper quantitative microbial risk analysis. This ensures that the water is kept safe and pathogens do not spread to an unacceptable extent, which would make many people sick

climate, humidity, air pollution and health.

therefore always be a core element in recreational

In addition, the sound and view of water are

water designs. The required water quality always

always a pleasure for people – both adults and

depends on what it is to be used for. For instance,

children alike. Along with this, the increasing

an acceptable level of microbial organisms in an

risk of extreme weather events and heavy

aquarium is higher (poorer water quality) than

rainfall causing damage in urban areas can be

the acceptable level of microbial organisms in an

tackled with integrated solutions that both

outdoor city swimming facility, where bathers

deal with the water and provide citizens with

may ingest the water. In the design of water

recreational value at the same time.

environments­ , an assessment of health risks

HANS-JØRGEN ALBRECHTSEN Professor, Department of Environmental Engineering TECHNICAL UNIVERSITY OF DENMARK

Rootzone treatment, Netherlands The open-air swimming pool in Amersfoort in the Netherlands uses local groundwater and each day 3–15 cubic metres (800-4,000 US gallons) of fresh water is pumped into the pool, depending on the levels of evaporation and other kinds of water loss. Dimensioned for the needs of 2,500 visitors a day, the water is circulated­and treated in a constant flow around a 300-square metres rootzone island. The volume of the pool is 5,000 cubic metres (1.3 million US gallons) and each day 150–600 cubic metres of water (40,000-160,000 US gallons) is filtered and treated by the rootzone filter constructed with a high content­of hard lime sand. The rootzone is covered with reeds – Phragmetis Australis – and is part of the natural wetland. (Courtesy: Transform Danish Rootzone Technology)

should therefore always be conducted to define an Ensuring safe water always important

acceptable level of safety and a correspondingly­

Builders, architects, landscapers, engineers

acceptable level of water quality. An acceptable

and artists are thus integrating water

risk could be equal to the risk accepted in the

as a key feature in urban environments.

European Bathing Water Directive. Such a risk

Recreational­water extends from fountains,

assessment comprises a hazard identification

water sculptures­, aquariums and park lakes

(what are the relevant pathogens), evaluation of

over swimming pools and wellness centres

exposure (pathogen dose) and calculation of the

to outdoor city baths and beaches. Many try

risk of infection. Any requirements for treatment

to avoid the use of chemicals because of their

efficiency to the applied treatment systems are

many negative aspects, but in all recreational

thus determined by comparing the acceptable

situations where people are exposed to water

quality with the quality of the available water.


Independent advisor ensuring best technical solution, Denmark In some cases it is of great value to not just rely on technology providers, but to hire an independent advisor to help decide on the best technical solution. The Blue Planet in Copenhagen, which is currently northern Europe’s largest and most modern aquarium, used an independent consulting­company when designing what is today the most advanced – but also most cost-effective – water treatment system for aquariums. The many advanced recirculation solutions and different types of water to be treated fill the basement of the aquarium with 4,500 square metres (nearly 50,000 square feet) of advanced technology. The tender documents and the associated technical requirements were prepared by a Danish consulting company with the main goal of minimising the energy and water consumption. Each of the 12 recycled water treatment plants was thus systematically described and the potential resource savings were defined. For instance, to save energy, emphasis was placed on placing each water treatment plant at the same height as the actual aquariums, and on using pipework with a low pressure drop. The contractor was also asked to establish drives for pumps and use energy-saving pumps. To save water, for instance, the salt water aquariums take in water from the sea at a depth of 10 metres and 1,600 metres in the sea when the salinity is high enough, the water for plants in the Amazon and freshwater aquariums are collected rainwater. The backwash water from all the filtration steps is passed to a shared tank where it is cleaned and then reused. (Courtesy: COWI)


If your goal is water efficiency, Denmark is ready as a partner

Danish water companies have shown their courage and drive by working with their competitors in order to create the Rethink Water platform. They are showing the world that Denmark is ready to take responsibility and contribute to finding solutions to the major water challenges the world faces KIRSTEN BROSBØL Minister for the Environment DENMARK

Denmark is surrounded by water, yet freshwater

For mutual benefit

is still a scarce resource for us. For 30 years,

As a country, we see great opportunity for

we have been rethinking water and building

mutual benefit in the transfer of knowledge

expertise within water efficiency. Today, our tap

and the growth in both partners’ business.

water is as pure as the finest spring water and

Our expertise is in assisting customers and

the water in the harbour of Copenhagen, our

stakeholders reach safe and effective water

capital, is so clean that people swim in it.

solutions, while developing their ability to profit from that knowledge. In our work we maintain

Denmark knows water

a healthy respect for different perspectives and

The knowledge we have about water resources,

agendas, as well as for the environment.

water security and water efficiency is no coincidence. Successive governments have

Rethinking water together

addressed our country’s limited natural resourc-

Rethink Water is a global network specialising in

es, concentrating on using them efficiently, and

water efficiency. So far, we are over 60 consult-

as a nation we strive to provide a safe, pleasant

ing companies, technology providers, utilities,

and healthy environment for people to live in.

research institutes and governmental bodies. The network brings together an unusually

Knowledge transfer

diverse and valuable mix of clients, consultants,

Denmark is not physically powerful, but know-

researchers, technology experts and govern-

ledge is power. Long ago we as Vikings spread

mental bodies. We have joined forces to share

fear across the seas. Today, we want to spread

knowledge and create even better water

something entirely different: knowledge and

solutions, in Denmark and around the world.

collaboration on how to globally protect water

We invite you in to collaborate on solving your

resources and improve water efficiency. Water

water challenges and to explore our expertise

is an increasingly scarce resource in most parts


of the world. We need to rethink how we use it. Technology companies

Customers and their stakeholders worldwide

Solutions for water efficiency

Research organisations

Export credit agency Consulting companies

Government and Public authorities

Organisations Water utilities


Find more white papers, learn more about the Rethink Water network and get in touch with us at:

Consulting companies Alectia Bonnerup Consult COWI EnviDan Gromtmij Moe & Brødsgaard Orbicon NIRAS Rambøll TREDJE NATUR Øllgaard

Technology companies Adept Water Technology AKVA group Denmark Aquaporin AVK Billund Aquaculture Biokube Blue Control Danfoss Danish Rootzone Technology EcoBeta Envotherm Freewater Grundfos HOH BWT I -GIS Kamstrup LiqTech International MJK Automation Mycometer NOV Flexibles Novozymes OxyGuard International PROAGRIA Environment RK Plast Scandinavian No-Dig Centre Siemens Silhorko-Eurowater SkyTEM Surveys Sorbisense Stjernholm UltraAqua Wavin Aarhus Geophysics Per Aarsleff Research institutes & demonstration projects Danish Technological Institute DHI Geological Surveys of Denmark and Greenland Kalundborg Industrial Water Demonstration Site Water utilities Greater Copenhagen Utility VCS Denmark North Water Aarhus Water Organisations related to water Association of Waterworks in Denmark AquaCircle aquacircle .org Copenhagen Cleantech Cluster Confederation of Danish Industry Danish Water Technology Group Danish Water and Wastewater Association Danish Water Forum Danish Water Services State of Green Consortium Water In Urban Areas Network

BW Negative Logo / State of Green Grey C - M 0 - Y - K 10 Dark C0-M0-Y0-K0

Governmental bodies & other sponsors City of Copenhagen Capital Region of Denmark Danish Trade Council Danish Ministry of the Environment Danish Nature Agency The Branding Denmark Fund

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