Bruce E. Beddow, P.E. Harald Kannewischer, dipl. Ing.Normen (DIN) 19643 Treatment and Disinfection of Water for Bathing Wa-ter, and the Swiss, Schweizerischer Ingenieur und Architekten-Verein - [PDF Document] (2024)


    © Reproduction is Prohibited, 1995.

    0. Introduction

    Water treatment process equipment in

    commercial swimming pools is the

    heart of the technical system and re-

    quires special care during the planning

    and arrangement of the selected system

    components. Special attention is also

    required to operate the system success-


    Significant advances in water treatment

    technology have been made over the

    past five years. Many improvements in

    system design and available equipment

    have been developed in Europe because

    of the stringent regulations on public

    swimming pool water quality in Euro-

    pean countries. European design stan-

    dards and equipment, especially from

    Germany, are making their way into the

    American market place. These stan-

    dards have been developed over many

    years as public pools and their use have


    Pools are no longer thought of as simp-

    ly swimming pools. They are classified

    by function, such as hot whirlpools,

    warm water massage pools, therapy

    pools, water attraction (leisure) pools,

    exercise pools, mineral pools, and of

    course swimming pools. Each type of

    pool design should consider, water

    temperature, bather frequency, water

    surface area and specific loading capac-

    ity of the chosen water treatment sys-

    tem process, as well as other criteria

    outlined in this paper.

    Water treatment systems have three

    main components:

    11.. PPooooll HHyyddrraauulliiccss

    Distribution of disinfectant and

    heated pool water return

    Optimal removal of unwanted

    particles present in the pool

    22.. WWaatteerr TTrreeaattmmeenntt SSyysstteemm

    Modern systems contain the following


    Flocculation, filtration and auto-

    matic water balancing

    This provides:

    Removal of impurities and un-

    wanted particles present in the wa-


    Optimum pH-value regulation and


    33.. DDiissiinnffeeccttiioonn

    Modern systems contain one of the

    following disinfectants:

    Hypochlorous acid (HOCL)

    Hypobromous acid (HBrO)

    Ozone w/HOCL or HOBr residual

    in the pool

    These three main components are each

    a functioning unit and must be consi-

    dered together as a total working sys-


    Incorrect conception and design, im-

    proper operation of equipment, impro-

    per maintenance or system failure can

    cause an unsuitable pool water quality

    and allow a possibly unhygienic situa-

    tion to develop.

    Optimization or economical renovation

    of water treatment systems is usually

    performed after identifying one or more

    of the following:

    1. Poorly functioning or defective

    system components.

    2. Poor pool water quality.

    3. High operating costs.

    Improving these conditions is the goal

    for either optimization or economic

    renovation of the system, and should be

    kept in mind while reading this paper.

    This paper looks at current American

    and International pool water quality

    standards and the important considera-

    tions for proper planning,

    design and operation of the individual

    system components, as well as the

    function of the entire system. It identi-

    fies important functions of public

    swimming pool water treatment sys-

    tems and is intended to assist individu-

    als responsible for the safety and opera-

    tion of public swimming pools.

    Additional information concerning

    public swimming pool design can be

    obtained from B2E Consulting Engi-

    neers, PC, Leesburg, VA. An "Availa-

    ble Publications" list is also available.

    1. Considerations for the Design and Renovation of New andExisting

    Pool Water Treatment Systems

    Improper function of individual com-

    ponents or of the entire system can lead

    to unsatisfactory hygienic conditions in

    the pool and increases the personnel

    expenses for service, care and repair.

    Frequently, the unsatisfactory purifying

    effect of such systems are compensated

    for by higher introduction of chemicals

    and fresh water. This diminishes bather

    comfort and increases operating costs.

    1.1 Water Circulation Capacity

    Calculation and sizing of water treat-

    ment equipment requires knowledge of

    the available valid local, national and

    sometimes international standards.

    Local standards, such as adopted by

    state regulating agencies, are usually

    helpful, but do not offer practical in-

    formation concerning the performance

    of a given water treatment process.

    National standards, such as provided by

    the National Spa and Pool Institute

    (NSPI), which is approved by the

    American National Standards Institute,

    Inc. (ANSI), are voluntary standards

    based on consensus agreement. This

    means that use of this standard by regu-

    lating agencies is voluntary and in the

    judgment of the ANSI Board of Stan-

    dard Review, substantial agreement has

    116 N Edwards Ferry Road, NE, Leesburg, VA 20176

    Bruce E. Beddow, P.E.

    Harald Kannewischer, dipl. Ing.


    © Reproduction is Prohibited, 1995.

    been made by directly and materially

    affected interests (or organizations).

    Some international standards, such as

    the German, Deutsches Institut fuer

    Normen (DIN) 19643 Treatment and

    Disinfection of Water for Bathing Wa-

    ter, and the Swiss, Schweizerischer

    Ingenieur und Architekten-Verein

    (SIA) 385/1 Requirements on Water

    and on Water Treatment Systems in

    Community Pools, are national laws

    effective throughout the entire country,

    and they are enforced. They clearly

    define acceptable water treatment

    processes, and accept substitutions to

    these standards only after the system

    has been put into operation, is tested

    and meets the conditions of the stan-

    dard. When a system is inadequately

    designed or falls out of compliance the

    pool is shut down.

    The German DIN Standards are recog-

    nized around the world as one of the

    most comprehensive international stan-

    dards and are available in English.

    Although they are one of the best, the

    requirements can be more difficult to


    For example, the American NSPI Stan-

    dard for whirlpools states that the water

    circulation rate should be sufficient to

    circulate the entire spa water capacity

    at a minimum of once every thirty mi-

    nutes. Since a typical system connected

    to two six person whirlpools contains

    roughly 15 m3 (4,000 gal) of water, the

    required water circulation rate is 30

    m3/h (130 gpm). The German DIN

    Standard bases the water circulation

    rate on bather load and the frequency of

    bathing. Working through the calcula-

    tions yields a circulation rate of 108

    m3/h (475 gpm) and 90 m3/h (400 gpm)

    when ozone is used. This shows a sig-

    nificant difference in required water

    circulation between the two standards.

    This subject will be discussed in more

    detail in subsequent sections of this


    When designing to either the American

    or German standard the following con-

    siderations should be made when plan-

    ning or evaluating special use pools:

    CChhiillddrreenn’’ss'' ssppllaasshh ppoooollss::

    If these water playing areas are fur-

    nished with a variety of special splash

    equipment, then a higher filter capacity

    is required, and should be sized in ac-

    cordance with the number of bathers

    and the higher frequency of bathing.

    Otherwise these pools will maintain a

    lower hygienic quality.

    HHeeaatteedd ppoooollss aanndd mmaassssaaggee ppoooollss::

    These pools typically have smaller

    water surfaces and are frequently over-

    loaded at public facilities. Considera-

    tion of the necessary water surface area

    for the expected number of bathers is

    absolutely necessary. This will reduce

    the possibility for building an under-

    sized pool at an unusually high cost.

    WWaatteerr SSlliiddeess::

    These attractions require a properly

    sized treated water circulation rate

    calculated in accordance with the fre-

    quency of use. For example, 80 people

    enter the slide circuit 10 times per hour

    for a total of 800 runs per hour. This

    would require a treatment capacity of

    160 m3/h (700 gpm) or 0.2 m3/h run

    (0.9 gpm/run).

    HHoott WWhhiirrllppoooollss::

    These pools require special attention

    and are the subject of a separate paper

    by the same author and available

    through B2E Consulting Engineers,

    P.C., Leesburg, VA.

    The performance of the pool

    water treatment system is not

    constant because the water

    flow is not constant over

    time. The flow rate reaches a

    maximum value immediately

    after the backwash cycle,

    and then falls off slowly

    until the filter resistance

    climbs to its maximum value

    before the next backwash


    After the backwash cycle the filter

    resistance across the sand filter

    amounts to roughly 0.1 bar (1.5 psi)

    and climbs until the next backwash

    cycle approximately 0.5 bar (7.3 psi).

    The filter should be equipped with

    pressure measurement gauges, and each

    pool system should have a suitable

    water flow meter. Good flow measure-

    ment devices are:

    Inductive process (expensive,

    precise, reliable)

    Flow meter (rotometer)

    Pitot manometer

    Paddle wheel flow sensor

    An inspection of the total system per-

    formance is also possible by establish-

    ing the pressure difference across the

    main circulation pumps using the ap-

    propriate manufacturer's pumping per-

    formance curve.

    It is possible that during operation the

    water flow can drop-off. The cause can

    be one or more of the following:

    Corrosion in the prefilter causing

    restricted flow

    Packing of the filter bed

    Corrosion of the pump impeller or


    Calcium build-up in the heat ex-


    Build-up of dirt, scale, etc.

    When evaluating a system the meas-

    ured water circulation flow rate should

    be obtained. According to the sizing

    requirements the proper circulation

    capacity is measured immediately be-

    fore the backwash cycle, and this min-

    imum flow rate should also be provided

    when a filter is clogged. After the

    backwash cycle a higher water flow

    rate will be pumped to the pool water

    distribution system. (See Figure 1)

    1.2 Pool Water Overflow and Return

    Even the best treatment systems are

    ineffective if the treated pool water

    return is inadequately distributed

    throughout the entire pool volume. An

    exact water distribution provides even

    mixing of disinfectant within 5 to 8

    minutes. Fast mixing of the total water

    volume and efficient removal of sur-

    face debris and impurities are important

    considerations for optimal system oper-



    © Reproduction is Prohibited, 1995.

    Pool water overflow should be hydros-

    tatically balanced using a pool over-

    flow rim/gutter. Pool rims/gutters of

    various architectural designs are an

    important component of the hydraulic

    system, and should be engineered. This

    ensures that the pool water displace-

    ment and overflow will be channeled to

    the balance tank. (See Figure 2)

    1.3 Prefilter/Fiber Screen

    A mesh fiber screen is required to catch

    large particles before the circulating

    pumps. A prefilter is especially impor-

    tant with outdoor pools where large

    quantities of foliage and similar impuri-

    ties are expected. It is frequently rec-

    ommended for outdoor pools to install

    a large filter element before the balance

    tank. Specially designed pool pumps

    should be considered for ease of main-

    tenance. (See Figure 3)

    Figure 3: Compact pool water circula-

    tion pump with built-in suction strainer.

    1.4 Flocculation

    Flocculation at the sand filter alone is

    unreliable, and can be helped using a

    flocculating agent, such as aluminum

    sulfate, iron (+3) chloride or more re-

    cently polyaluminum chloride (AlCl3)

    or (PAC). These flocculates

    only work between a limited pH range

    and require a certain reaction time.

    Aluminum sulfate is effective between

    the range of pH-6.8 to 7.2. With higher

    pH-values the flocculation will be de-

    layed and leads to cloudy water in the

    pool. Flocculation will not be achieved

    with a pH level above 7.4. Today PAC

    is predominantly used because it is less

    pH sensitive and provides better water


    Dosage levels are typically from 0.3 to

    1.5 g/h per m3/h (6.8 - 9.5 g/h per 100

    gpm) of the required water circulation


    It is important that the relationship

    between pool water loading and floccu-

    late injection is given. Flocculation for

    outdoor pools is dependent on both the

    weather and the number of bathers. For

    example, rainy days usually require 0.3

    g/h per m3/h (6.8 g/h per 100 gpm) and

    peak days 1.0-1.5 g/h per m3/h (23 - 34

    g/h per 100 gpm). This is likewise true

    for indoor pools where the number of

    visitors is changing from day to day.

    The injection point should be chosen

    near the pump discharge, so that optim-

    al mixing is achieved. The injection

    coupling should be fixed in the center

    of the flow area of the piping and

    should have a nozzle to distribute the

    flocculating agent.

    1.5 Filter

    A pressurized sand filter functions only

    as well as the backwash can provide the

    proper cleaning effect. Backwash is

    usually performed as a function of the

    pressure drop across the filter. This

    normally occurs every 1 to 5 days. The

    filter must be backwashed at least once

    per week, even when the pressure

    gauges indicate that the filter medium

    is not completely filled.

    Example of a semi-automatic backwash


    1. Drain the filter to the sand level

    2. Clean air washing for 5 minutes

    3. Mixed water/air washing from 7-

    10 minutes

    4. Clean water washing from 3-5


    5. Filling the filter vessel

    6. First filtrate directed into the sani-

    tary sewer (2-3 minutes)

    Air washing is an important considera-

    tion because it fluidizes the sand bed.

    The air lifts the sand and the grains

    rotate and move against one another.

    This action allows dirt fixed to the

    grains of sand to be washed out.

    The washing process, lifting the sand

    bed and actual fluidization, should be

    inspected with open filters. Under these

    conditions it is also possible to use a


    © Reproduction is Prohibited, 1995.

    stick (sounding rod) to determine

    whether the sand bed is clogged. With

    open filters it is certain that uneven or

    unsymmetrical air/water patterns can be


    Figure 3

    1. Casing

    2. Impellar

    3. Rear Wall

    7. Motor

    11. Casing Seal

    12. Drain Plug

    13. Impellar Nut

    17. Mechanical Shaft Seal

    18. Filter Housing

    19. Strainer

    20. Cover

    21. Blockage Check Point

    22. Manometer Connection

    23. Casing Seal

    24. O-Ring

    25. Casing Seal Ring

    26. Star Handle

    During the filter backwash seven

    valves service each filter controlled by

    an exact time program. The exact regu-

    lation of the projected backwash pro-

    gram and regulation of the seven valves

    can only be accomplished using an

    automatic control system.

    (See Figure 4)

    It is especially important to be aware

    that during the operation adjustments

    cannot be made. Because of the low

    back pressures during backwash, it is

    important to have good throttling of the

    valves. The system is then able to oper-

    ate with reduced pumping capacity.

    With high back pressures during the

    air/water backwash there will be little

    or no air in the filter, which is undesir-


    For this reason backwash without back

    pressure is required. This means that

    with an open inspection port the back-

    wash must operate perfectly. A high

    water drain connection is therefore not


    It is likely that long operating cycles

    will allow calcium build-up in the filter

    media with hard water or pools with

    high pH-values. This can be such a

    problem that the media (sand) must be

    broken-up with a compressor. Addi-

    tional calcification of the filter can

    result in water bypass through channels

    in the media, and result in insufficient


    The filter bottom is basically a baffle

    (60-70 holes/m2 or 6-7 holes/SF). The

    holes or nozzles provide an even flow

    of filtrate and backwash water. The

    main supply connections and filter

    distribution network should be de-

    signed to distribute the water and air

    evenly. If the internal filter distribution

    is designed poorly a portion of the me-

    dia will be backwashed with air and

    another with water.

    1.6 Rim/Gutter Overflow Control

    During Pool Deck Cleaning

    A redirection of the pool overflow wa-

    ter is necessary when cleaning fluid is

    not permitted in the filter. Cleaning

    fluid introduced into the filter leads to

    mud (slime) build-up during the back-

    wash cycle. The problem occurs when

    cleaning fluid is held in the filter vessel

    after the backwash cycle, because the

    dissolved dirt will be pumped into the

    pool. It is best to generously redirect

    the channeled water containing clean-

    ing agents automatically to the sanitary

    sewer. (See Figure 5)

    1.7 Important Chemical Parameters

    for Water Treatment

    General knowledge of the water analy-

    sis of the available drinking water,

    available from the local water authori-

    ty, is needed for the planning, renova-

    tion and operation of pool water treat-

    ment systems.

    1.7.1 Water Hardness

    The three different measures of water

    hardness are:

    Calcium Hardness (Temporary


    Non-calcium Hardness (Other


    Total Dissolved Sol-

    ids (TDS)

    TDS is the sum of calcium and

    non-calcium hardness.

    The calcium hardness is the

    most interesting value of water

    hardness for swimming pool

    applications. Calcium hardness

    consists of both carbonate and

    bicarbonate ions.

    In nature carbonic acid rich

    water combines with calcium

    carbonate (lime) as shown by

    the following reaction:

    CaCO3 + H2CO3 Calcium Carbonate Carbonic Acid

    Ca(HCO3)2 Calcium Bicarbonate

    Calcium or magnesium are practically

    insoluble in pure water. The calcium

    hardness is therefore dependent upon

    the carbonic acid content of water.

    The stability of calcium carbonate and

    carbonic acid in water is both tempera-

    ture and pressure dependent.

    As water containing carbonic acid is

    heated carbon dioxide off-gases and the

    Ca(HCO3)2 CO2 + H2O + CaCO3 HEAT


    © Reproduction is Prohibited, 1995.

    calcium hardness rises, as shown by the

    following reaction:

    Carbon dioxide also off-gasses when

    heating pool water and the pH-value

    begins to rise. As a result calcium car-

    bonate can precipitate out of solution,

    which is evident as the water quickly

    becomes turbid. Continuous pH correc-

    tion, usually with muraitic acid (diluted

    hydrochloric acid) or hydrochloric acid,

    is necessary.

    In order to reduce the amount of cal-

    cium precipitate and to regulate the pH-

    value, hydrochloric acid is normally

    injected into the pool water return. The

    hydrochloric acid, which is a stronger

    base than carbonic acid, displaces the

    carbonic acid according to the follow-

    ing reactions:

    The resulting carbonic acid disasso-

    ciates into,

    and the resulting calcium chloride

    (CaCl2) is very soluble in water and

    will not precipitate out of solution.

    Hard water requires pH regulation with


    Soft water requires special attention to

    determine whether to regulate with

    calcium bicarbonate (soda ash), phos-

    phates or with marble chips.

    During chlorination injecting free hy-

    drochloric acid in water requires suffi-

    cient acid capacity (water hardness),

    otherwise the pH-value may fall-off

    sharply to values below pH-7.

    Sodium hypochlorite can be an appro-

    priate choice as the disinfectant in

    pools with soft water.

    1.7.2 pH-Value

    The pH-value is the measure of the

    hydrogen ion concentration in water

    solutions. It is the negative exponent of

    the hydrogen ion concentration as

    shown by the following equation:

    PH = log [H+] = log (1 / [H + ]) Where,

    [H + ] = concentration of hydrogen

    ions [moles/liter ]

    The pH-value is a significant factor for

    proper water quality and influences the


    The germ destruction rate (ORP)

    The effectiveness of the flocculation


    Calcification and corrosion in the


    Reduction of combined chlorine

    The normal pH-range should lie be-

    tween pH-6.8 and 7.4. The ideal value

    is pH-7.2.

    Careful attention of the pH-value is not

    only necessary for stabilization of the

    water hardness, but also to achieve

    optimal effectiveness of chlorine disin-


    The effectiveness of chlorine as a disin-

    fectant in water is strongly dependent

    upon the pH-value of the water.

    (See Figure 6)

    pH-6 With chlorine gas injection,

    resulting in 97 % hypochlorous

    acid (free chlorine, HOCl) and 3

    % hypochlorite ion, which is less


    pH-7 Results in only 78 % hy-

    pochlorous acid (HOCl).

    pH-8 Results in only 24 % hy

    pochlorous acid (HOCl).

    Therefore, it can be seen that as the pH-

    value climbs, significantly greater

    quantities of chlorine are necessary to

    maintain proper chlorine residuals in

    the pool water.

    Ca(HCO3)2 + 2 HCl CaCl2 + 2 H2CO3


    CaCO3 + 2 HCl CaCl2 + H2CO3

    H2CO3 CO2 + H2O


    © Reproduction is Prohibited, 1995.

    If the pH-regulation system is not func-

    tioning properly high concentrations of

    acidic or soft water can be pumped into

    the pool. This can result in corrosion

    and cause cracking of the pool surface


    In addition, it is important to notice that

    acid vapor in the area of chemical in-

    jection equipment will cause immediate

    corrosion. Therefore, chemical rooms

    should be closed and ventilated.

    1.7.3 pH-Value Regulation with Car-

    bon Dioxide

    Private hotel pools and sometimes

    thermal pools are well served by carbon

    dioxide (CO2) for pH-regulation.

    Therefore, the solubility of CO2 in

    water must be examined.

    Hard water treatment systems with high

    circulation rates require higher con-sumption of CO2. Theinjection must

    occur in regions of high water pressure.

    Good injection points are immediately

    before or after the filter. The sizing and

    arrangement of the injectors is very

    important for an even distribution. The

    injection should be continuous and in

    small quantities. Carbon dioxide pH-

    regulation is very expensive for public

    pools. The advantage, however, is that

    chlorine concentrations in the pool

    water tend not to increase and remain

    more stable than with use of hydroch-

    loric acid (HCl).

    Highly loaded pools with hard water,

    for example, hot whirlpools or massage

    pools, which are treated with chlorine

    gas can maintain pH-values 7 without

    the addition of muraitic acid (diluted

    hydrochloric acid). This is conditional,

    however, on the additional disinfectant

    required to maintain the desired resi-

    dual hypochlorous acid concentration.

    In this case, where pH-value measure-

    ments, with for example phyenol red,

    indicate falling pH-6.8, the fresh water

    intake will be increased or a marble

    tower will be built into the design.

    The acid consumption in hard water

    climbs faster with attractions like wa-

    terfalls and slides. This creates an un-

    favorable, higher concentration of acid

    in the balance tank. In addition, acid

    consumption increases through unne-

    cessarily high temperatures at the sur-

    face of the heat exchanger.

    1.7.4 Oxidation Potential

    The concentration of reductant (organic

    impurities) in the pool water can be

    measured as the potassium permanga-

    nate (KMnO4) consumption of the wa-

    ter tested. Permanganate ion (MnO4-), a

    deep purple solution, is used to meas-

    ure oxidation of these organic impuri-

    ties which maintain a residual concen-

    tration in pool water. The permanga-

    nate solution is added to the sample and

    is reduced. When the sample turns

    purple the reductants have been oxi-

    dized and the permanganate consump-

    tion is measured. The following half

    reaction shows the reduction of per-

    manganate ion:

    MnO4 - (aq) Mn + 2 (aq)

    Each bather brings a certain quantity of

    impurities into the pool water. This has

    been documented as 0.8-1.0g combined

    nitrogen compounds, measured as

    NH4+, which could be either from urine

    or sweat. It has also been shown that

    each bather brings approximately 50-70

    ml of urine into the pool, and that a

    residual concentration of 0.5-1.0 mg/l

    (ppm) of urine can be found in pool

    water. The German Standard, DIN

    19643 quantifies this amount to corres-

    pond to a potassium permanganate

    consumption of approximately 2-6 g


    The higher value is valid for pools with

    higher temperature and increased water

    movement, such as in hot whirlpools.

    The standard impurity concentration is

    formulated in the German, DIN 19643


    "The average amount of impurity

    brought into the pool by one person

    during the length of stay is characte-


    © Reproduction is Prohibited, 1995.

    rized by the reduction potential as

    measured with potassium permanga-

    nate consumption in grams of oxygen

    per person, where 1 g O2 ( 4 g

    KMnO4) is the basis."

    The potassium permanganate consump-

    tion is measured at the pool water over-

    flow rim/gutter and at the pool water

    return, basically before and after the

    sand filter. The difference in the

    KMnO4 consumption required to oxid-

    ize the reductant of water before and

    after the filter is used to calculate the

    specific loading capacity of the water

    treatment system, where each water

    treatment process has an associated

    specific loading capacity. This equation

    is shown below:

    Ox V= E P (1)


    Ox Difference in the reduction of Mn

    VII II from overload and return water [g/m3 (ppm)]

    V Treated water volume [m3 ]

    E Standard impurity quantity [g]

    P Number of bathers

    The specific loading capacity (loading

    factor), b-value, per person for a specif-

    ic water treatment process can be ob-

    tained as follows:

    b = Ox / E = P / V [1/m3] or per-

    sons/m3] (2)

    where, the standard impurity quantity


    1 g O2 ( 4 g KMnO4)

    For example:

    An existing pool water treatment sys-

    tem has a measured overflow water

    KMnO4 consumption value, Ox, ow =

    6 g/m3 (ppm) and a return water con-

    sumption of, Ox,Rw = 4 g/m3 (ppm).

    The loading capacity of the water

    treatment system is:

    Ox = Ox,Ow - Ox,Rw KMnO4 [g/m3


    E = 4 g KMnO4

    b = 2 g/m3 / 4 g b = 0.5 1/m3

    This specific loading capacity (loading

    factor) will be used in Section 4.0 of

    this text to determine the proper water

    circulation rate of the water treatment


    The b-values for several water treat-

    ment processes have been determined

    empirically with the following results:

    1. b = 0.5 1/m3

    flocculation + filtration + chlorination (3-step process).

    2. b = 0.6 1/m3 flocculation + filtration + ozonation + ac-

    tivated charcoal filtration + chlorination

    (5-step process).

    3. b = 0.5 1/m3

    adsorption to activated charcoal powder + diatomaceous earthfiltration w/ activated

    charcoal powder + chlorination.

    In addition, it should be pointed out

    that the measured potassium perman-

    ganate consumption of the pool water

    return, Ox, Rw, should not exceed a

    value greater than 3 g/m3 above the

    fresh water (potable water) supplied by

    the local water treatment plant.

    1.7.5 Oxidation Reduction Potential

    The oxidation reduction potential is the

    measurement of the germ killing veloc-

    ity of the treated pool return water and

    is influenced by the pH-value, the free

    chlorine content, the fresh water intake

    as well as the concentration of reduc-

    tant. The oxidation reduction potential

    is therefore a parameter for overall

    judgment of the water quality.

    Correct values for good water quality

    with water treatment systems using

    chlorine as the disinfectant, measured

    with a mercury chloride (Hg2Cl2) elec-

    trode and a pH-range between 6.5-7.5

    should be > 700 mV.

    The oxidation reduction potential

    should not be used to control disinfec-

    tant injection, but should be measured

    and registered and serves as a confir-

    mation of proper pool water quality.

    1.7.6 Chlorination

    When using chlorine gas it should be

    mixed into the pool water return using

    an injector located in the injector by-

    pass piping, whereby in acidic and

    neutral pH-ranges hypochlorous acid is

    formed. When the pH-value is too high

    hypochlorous acid concentration re-

    mains low and hypochlorite ion, which

    is significantly less effective as a disin-

    fectant, may dominate.

    Injection of chlorine in water results in

    the disassociation of elemental chlorine

    into hydrochloric acid and hypochlor-

    ous acid as shown below:

    Cl2 + H2O + HCl + HOCl

    Cl2 = Chlorine H2O = Water

    HCl = Hydrochloric Acid

    HOCl = Hypochlorous Acid

    or reaction in the presence of calcium

    bicarbonate into hypochlorous acid,

    calcium chloride and carbon dioxide as

    shown below:

    2Cl2 + Ca (HCO3)2 2HOCl + CaCl2 + 2 CO2

    2Cl2 = Chlorine

    Ca (HCO3)2 = Calcium Bicarbonate

    2HOCl = Hypochlorous Acid CaCl2 = Calcium Chloride

    2 CO2 = Carbon Dioxide

    When chlorine gas is used a full va-

    cuum pressure regulator and venturi

    injector system is recommended. This

    ensures, that in the event of a chlorine

    gas line break, air will be drawn into

    the distribution line preventing chlorine

    from escaping. The regulator will au-

    tomatically shut-off upon sensing rela-

    tive overpressure.

    The minimum residual concentration of

    active (free) chlorine in pool water for

    normal use pools should not fall below

    0.3 mg/liter (ppm). This value is sub-

    ject to locally adopted codes and regu-


    The germ killing velocity of chlorine as

    a disinfectant in water is very good,

    much faster than with bromine. The

    residual free chlorine concentration in

    pool water should be sufficient to kill

    99.9% of E. Coli within 30 seconds.

    Combined chlorine and the byproducts

    of breakpoint chlorination are oxidized

    products, and cannot be completely

    removed from the pool water. For this

    reason a constant supply of fresh water

    (fresh water intake) is recommended. Free Chlorine

    Hypochlorous acid (HOCl) or “free

    chlorine” is a very weak acid and dis-

    sociates quickly as pH rises above 6 as

    shown below:

    HOCl H+ + OCl-

    HOCl = Hypochlorous Acid

    H+ = Hydrogen Ion


    © Reproduction is Prohibited, 1995.

    OCl- = Hypochlorite Ion

    Hypochlorous acid is a much stronger

    oxidant than hypochlorite ion and is the

    desired disinfectant in chlorinated

    swimming pool water. In order to op-

    timize the disinfection effect in pool

    water a pH - 7.0 - 7.4 is recommended.

    (See Figure 6) Combined Chlorine

    Upon introduction of ammonia (NH3)

    into the pool water from bather or am-

    monia laden make-up (fill) water, or-

    ganic amines are formed through the

    following reactions:

    NH3 + H2O NH4OH NH3 = Ammonia

    H2O = Water

    NH4OH = Ammonia Hydroxide

    NH4OH + HOCl NH4OCl + H2O

    NH4OH = Ammonium Hydroxide HOCl = Hypochlorous Acid

    NH4OCl = Ammonium Hypochlorite H2O = Water

    The ammonium hypochlorite is, as with

    most salts, a weak acid and disasso-

    ciates into water and monochloramine.

    NH4OCl NH2Cl + H2O

    NH4OCl = Ammonium Hypochlorite

    NH2Cl = Monochloramine H2O = Water

    The hypochlorous acid (free chlorine)

    reacts with the unwanted monochlor-

    amine to create dichloramine.

    NH2Cl + HOCl NHCl2 + H2O NH2Cl = Monochloramine

    HOCl = Hypochlorous Acid NHCl2 = Dichloramine H2O = Water

    In swimming pool applications (pH - 7

    to 8) monochloramine (96%) predomi-

    nates over dichloramine (4%). Breakpoint Chlorination

    When the combined chlorine concen-

    tration in the pool water climbs above ~

    1.0 mg/liter (ppm) breakpoint chlorina-

    tion is required to oxidize or “burn-up”

    the combined chlorine in the pool thus

    removing the chloramines. Breakpoint

    chlorination or “superchlorination” is

    performed by chlorinating the pool

    water to approximately 10 to 12 times

    the normally balanced residual free

    chlorine concentration. Destruction of

    combined chlorine, monochloramine

    and dichloramine, occurs rapidly be-

    tween pH - 7 and 8 according to the

    following reactions:

    2 NH2Cl + HOCl N2 + H2O + 3 HCL

    2 NH2Cl = Monochloramine

    HOCl = Hypochlorous Acid

    N2 = Nitrogen H2O = Water

    3 HCL = HydrochloricAcid


    NH2Cl + NHCl2 N2 + 3 HCl

    NH2Cl = Monochloramine

    NHCl2 = Dichloramine

    N2 = Nitrogen 3 HCl = Hydrochloric Acid

    Once breakpoint chlorination is

    achieved the free chlorine residual

    remains high and a chlorine neutralizer

    such as sodium bisulfate must be added

    to bring the residual free chlorine con-

    centration back to an acceptable level

    for bathing. Care must be taken not to

    overcompensate during neutralization,

    which would reduce the free chlorine

    residual below the required safe limits.

    If this occurs pool water chlorination

    must be accelerated to bring the resi-

    dual disinfectant concentration into

    compliance before bathers may enter

    the pool. (See Figure 7)

    17.6.4 Fresh Water Intake

    If the fresh water, provided by the local

    water authority, is of suitable quality

    then a constant supply of fresh water

    can be introduced into the pool to dilute

    the combined chlorine and byproducts

    of breakpoint chlorination. This will

    extend the period of time between

    which breakpoint chlorination is re-

    quired. In addition, it will reduce the

    concentration of dissolved salts in the

    pool, renewing the water, and make

    swimming more comfortable for the

    bathers. Providing fresh water helps to

    maintain the pool water balance and to

    prevent the build-up of unwanted com-

    pounds as shown in the table below:


    Max. Concentration

    Iron (Fe)

    Manganese (Mn)

    Ammonium (NH4+)

    < 0.1 mg/l (ppm)

    < 0.05 mg/l (ppm)

    < 2.0 mg/l (ppm)


    © Reproduction is Prohibited, 1995.

    Table Enrichment of the

    Pool Water in Salts, their Origin and

    Potential for Damage

    If the fresh water, provided by the local

    water authority, is not of suitable quali-

    ty, as shown in the table below, then

    either one of or a combination of the

    following may be necessary:

    1. Providing fresh water intake from an

    unpolluted on-site well. (Well water

    analysis required).

    2. Pretreating the fresh water with an

    activated charcoal powder/high rate

    sand filtration system.

    3. Continuously injecting activated

    charcoal powder into the pool water

    pumped discharge before the high

    rate sand filter to continually remove

    combined chlorine from the pool.

    (See Figure 8).

    4. Providing a corona discharge ozona-

    tor in either the 5-step, complex

    ozone or combi-block process ar-


    Table Requirements of the

    Fresh (Fill) Water Halomethanes

    Carcinogenic compounds are formed

    by the reaction of chlorine and bromine

    in swimming pool water. These com-

    pounds, halomethanes, are created by

    reaction of the disinfectant with bro-

    mides and organic impurities brought

    into the pool by the pool guests.

    The recommended maximum

    exposure to halomethanes in pool

    water is 10 g/liter (ppb). This

    value is taken from the

    “Deutsches Institut für Normung

    (DIN) 19643 Standard”.

    The common halomethanes are

    trichloromethane or “chlorform”

    (CHCl3), bromodichloromethan

    (CHBrCl2), dibromochloromethan

    (CHClBr2) and tribromomethane

    or “bromoform” (CHBr3).

    The following table shows the

    potential build-up of chlorine and

    bromine containing haloforms in

    chlorinated water with varying

    concentrations of typical organic

    impurities (bromide and organics).

    Table1.7.6.5 Halomethane Concen-

    trations in Pool Water with 2-3

    mg/liter (ppm) residual Cl2

    1 Normal bather load with guest showers before enteringpool.

    2 Normal bather load without guest

    showers before entering pool. 3 Insufficient pool watercircula-

    tion rate. (Does not meet DIN

    19643 Standard).

    Use of bromine instead of chlorine as

    the residual disinfectant increases ha-

    lomethane concentrations in the pool


    1.8 Removal of Impurities Found in Pool Water

    The following types of impurities exist

    in pool water:

    1. Suspended impurities (hard particles

    which are floating, such as hair, tex-

    tile fibers, dead skin, etc.)

    2. Dissolved colloidal impurities (se-

    cretions from the throat, nose, ears,

    fat from the skin, cosmetics, etc.)

    3. Completely dissolved impurities

    (sweat and urine)

    All of the aforementioned impurities

    are brought into the pool over the water

    surface. An intensive concentration of

    these impurities can be found in the

    uppermost 10-20 cm (4-8") of water

    depth. This is exactly where the bather

    is moving about with the most sensitive

    areas of the body, like the nose, ears

    and mouth.

    In spite of proper treated water distribu-

    tion and mixing and a large portion of

    the water lead to the overflow

    rim/gutter, denser particulate matter

    will sink to the bottom. This cannot be


    Figure 9 shows the general distribution

    of impurities and particulate matter in

    cross section through a typical pool.

    The problem exists and should be rec-

    ognized and considered during the

    design of the treated water return outlet


    The pool water distribution system is

    an important component in the water

    treatment system. In order to disinfect

    the pool evenly and thoroughly either a

    vertical or horizontal distribution

    should be used. If proper mixing of the

    residual disinfectant is not achieved

    dead zones can develop reducing pool

    water quality and causing an increase in

    the disinfectant injection rate and there-

    fore an increase in chemical consump-

















    1003 2003



    1.3 1.7



    1.2 1.6



    6.3 5.8



    7.7 5.3



    16.5 14.4


    Chloride Ion

    Corrosion of metal above

    ~ 150 mg/l (ppm) Cl-

    - All chlorine containing


    - Iron-III Chloride, Aluminum

    Chloride and Aluminum

    HydroChloride fluoculant

    hydrochloric acid


    Corrosion of concrete

    above ~ 150 mg/l SO42-

    - Aluminum-Sulfate (Floculant)

    - Sulfuric acid (pH-Regulation)

    - Sodium bisulfate


    Health risks from 20 mg/l

    (ppm) above the NO3-

    content of the freshwater

    - Oxidized destruction of urine

    and other nitrogen containing

    impurities (ie. Ammonium)


    Cloudy water and scaling,

    calcification of the filter

    media above ~ 70 mg/l

    - Dolomite filter material used for

    pH- stabilization

    - Leaching of mortar in tiled pools

    - Calcium hypochlorite disinfect-



    © Reproduction is Prohibited, 1995.

    Removal of the aforementioned impuri-

    ties is achieved in the following steps:

    Mechanical Filtration

    Flocculation and filtration



    1.8.1 Suspended Impurities

    These hard, floating particles should be

    mechanically filtered on the basis of the

    strainer effect, electrostatic effect and

    the wedge effect. The mechanical ef-

    fects of filtration are only effective for

    larger sized particles.

    1.8.2 Dissolved Colloidal Particles

    These dissolved colloidal impurities are

    negatively charged and repel one

    another. Flocculation allows these par-

    ticles to coalesce by aligning the

    charged particles whereby the colloids

    tend to ball-up forming larger particles.

    This effect increases the average size of

    the particles, therefore increasing the

    filtration efficiency of the system.

    These impurities can be effectively

    removed either by flocculation or ad-

    sorption on activated charcoal media.

    1.8.3 Completely Dissolved Impurities

    These completely dissolved organic

    impurities are primarily oxidized using

    chlorine or ozone. The oxidation

    process is incomplete in pool water

    which contains especially high concen-

    trations of organic matter. A small

    portion of these impurities are removed

    with direct contact with other flocculat-

    ing particles and are held in the filter


    These impurities can be effectively

    removed after flocculation by activated

    charcoal powder.

    A portion of these impurities and com-

    pounds are only able to be diluted with

    fresh water to the proper hygienic con-


    The fresh water intake is dependent

    upon the pool guests' frequency of

    bathing and on the water treatment

    process used.

    1.8.4 Special Conditions for Outdoor


    The impurities in outdoor pools are

    brought in partly due to the bathers and

    partly due to the atmosphere. The pool

    guests use the pool, unlike with indoor

    pools, without properly cleansing

    themselves before entering the water

    and usually more frequently. There will

    be a large quantity of sun cream, cos-

    metics, sweat and other impurities car-

    ried into the pool.

    Additionally, in the absence of small

    walk-thru pools at the entrance to the

    pool deck organic impurities from the

    sun bathing areas will be carried into

    the pool.

    Outdoor pools, contrary to indoor

    pools, will experience a very different

    number of bathers in relation to the

    number of fair and foul weather days. It

    is almost unavoidable to have an exces-

    sive number of bathers on beautiful


    The surrounding area and the pool will

    also be dirtied from wind and storms.

    Special problems frequently arise from

    trees planted near the pools.

    1.9 Heating

    The heat exchanger used to heat the

    pool water should be manufactured

    from series 316 stainless steel or better

    and be easily cleanable. A plate frame

    heat exchanger is recommended.

    In order to minimize carbonic acid off-

    gassing, a low primary hot water tem-

    perature should be supplied. The pool

    water can be heated using a bypass

    configuration with a bypass pump. This

    reduces energy consumption as well as

    the size of the heat exchanger. With

    this arrangement care must be taken not

    to heat the pool water above 45 C

    (115 F).

    For example, sizing for a primary

    hot water temperature of 50/35 C

    (120/95 F) with a pool water tempera-

    ture of 27/32 C (80/90 F).

    Lower primary water temperature re-

    quires greater heat exchange surface

    area, however, reduction of acid con-

    sumption required for neutralization

    of the pool water leads to an improve-

    ment of pool water quality for the bath-


    1.10 Balance Tank

    A balance tank is required for holding

    pool overflow water due to bather dis-

    placement and wave motion as well as

    backwash water. This tank requires the

    same hygienic conditions as the pool.

    That means, the tank should be tiled or

    surface coated, have a light and portal

    for inspection and have a proper means

    of entrance for cleaning.


    © Reproduction is Prohibited, 1995.

    A regular inspection and cleaning of

    the balance tank is necessary.

    The entrance to the balance tank,

    whether it be manhole or submarine

    door, must prevent the escape of vapor

    into the technical/filter room to protect

    equipment against corrosion.

    In addition, a vent is required to the


    The pool water overflow piping run-

    ning back to the balance tank should be

    provided with an open tee connection

    as shown in Figure 10. This helps to

    reduce the acid concentration as well as

    scale build-up in the balance tank by

    allowing CO2 to off-gas by the reaction

    of hydrochloric acid with calcium car-

    bonate and calcium bicarbonate in the

    pool water overflow piping.

    1.11 Water Distribution in Hidden


    Pool water return outlets under me-

    chanical floors, submerged pool covers,

    etc. are required to eliminate build-up

    of debris. It is usual to open the valves

    to these outlets during night setback

    mode for an hour to wash out these

    hidden spaces.

    2. Water Treatment System

    As mentioned in the introduction to this

    paper, the entire water treatment system

    is made up of the following compo-


    Pool Hydraulics

    Treatment System (with floccula-

    tion, filtration, and oxidation)


    When designing a pool water treatment

    system these three components must be

    thought of collectively in order to affect

    a well integrated and properly working


    2.1 Water Treatment

    Modern outdoor pools and lightly

    loaded indoor pools are usually well

    served by the 3-step water treatment

    process: Flocculation-Sand Filtration-

    Chlorination. The specific loading ca-

    pacity (loading factor) of this process

    is, b=0.5 1/m3. (See Figure 11)

    Highly loaded indoor pools, warm

    pools, hot whirlpools and therapy pools

    require the 5-step water treatment

    process: Flocculation-Sand Filtration-

    ozonation-activated Charcoal Filtra-

    tion-Chlorination. The loading factor

    for this process is, b=0.6 1/m3. (See

    Figure 12)

    The 5-step (Incl. Ozone) system may

    also be suitable for indoor training and

    competition pools in order to maintain

    good water quality, because of conti-

    nual high loading of the pool water

    throughout the day. This system offers

    better control and reduces the required

    flow of fresh water entering the pool.

    Three reliable ozone pool water treat-

    ment processes are the 5-step, Complex

    Ozone and Combi-Block arrangements.

    These systems can be essential in eli-

    minating “Hyper-Sensitivity Pneumoni-

    tis” a bronchial disorder caused by

    breathing aerosols containing endotox-

    ins (dead micro-organisms). This con-

    dition can occur in indoor swimming

    pools when the water temperatures are

    greater than 86 F or if the pool has


    © Reproduction is Prohibited, 1995.

    built-in attractions which agitate the


    Committing to one of the water treat-

    ment processes is one of the significant

    responsibilities of the consulting engi-

    neer. The influential factors to consider


    Indoor swimming pool

    Outdoor swimming pool

    Bather frequency

    Pool water temperature and use

    Potable water quality

    Potable water and waste water


    Operating costs

    Safety related items

    First Cost


    2.2 Disinfection

    Classic disinfection and oxidation is

    achieved using pressurized chlorine

    gas. Chlorine gas is usually delivered in

    65 kg (150 lb) steel bottles.

    The disinfection process may require

    chlorine gas or hydrochloric acid deli-

    very and storage which should be con-

    sidered in the planning and design

    phase of any project.

    The chlorine gas injection system is

    arranged with a bypass flow of pool

    water pumped across a low flow, high

    pressure pump. The water flows

    through a venture injector creating a

    vacuum on the connected chlorine gas

    distribution piping (flexible hose). The

    chlorine is drawn into the venturi and is

    mixed with the pool bypass water. The

    chlorine gas immediately disassociates

    into hypochlorous acid and hypochlo-

    rite ion. The relative concentrations are

    dependent upon the pH-value of the


    In addition, hydrochloric acid is

    present, which is usually ideal for water

    with average to high carbonate hard-

    ness, and serves to maintaining the pH-


    5-step systems use ozone for the oxida-

    tion process and chlorine as the residual


    Chlorine gas distribution technology

    has improved and allows engineers to

    design a full vacuum system. This type

    of system significantly improves the

    level of safety associated with chlorine

    gas distribution. These systems also

    provide automatic switching from an

    empty to a full bottle while the system

    is in operation.

    The danger of such systems is greatly

    reduced, and hangs solely on the chlo-

    rine gas bottle and valve itself. The

    weak points are the shut-off valve and

    the valve seal on the bottle. Of course,

    the pressure reducing valve and hous-

    ing of the vacuum regulator must be

    manufactured to handle the high pres-

    sure of full gas bottles.

    The following chlorine products can be

    used as alternatives to chlorine gas:

    Sodium hypochlorite:

    Delivered as a liquid


    © Reproduction is Prohibited, 1995.

    Contains ~ 150-170 g/liter (570-

    645 g/gal) active chlorine

    Strong alkaline solution, pH-10 to



    Well suited with soft water

    Simpler and less dangerous to

    handle than Chlorine gas


    Active chlorine concentration

    decays ~ 1 % per day or 3.8 g/gal

    day (be aware when storing for

    long periods)

    Sodium hypochlorite by electrolysis:

    Manufactured on site through

    electrolytic reaction with sodium

    chloride (NaCl, cooking salt) solu-


    Resulting solution contains ~ 2-5

    g/liter (8-20 g/gal) active chlorine

    3-4 kg (6.6-8.8 lb) of sodium chlo-

    ride and 5-6 kWh of electricity are

    required to manufacture 1 kg (2.2

    lb) of sodium hypochlorite


    Only NaCl (cooking salt) is re-

    quired which can be easily stored

    and handled

    Same as with delivered sodium

    hypochlorite for soft water appli-



    Sodium hypochlorite solution

    generated by the reaction of chlo-

    rine gas and hydroxyl ions in wa-

    ter must be stored in a large distri-

    bution tank

    Problematic with hard water, in-

    creased HCl consumption

    Chlorine gas detectors and alarm

    system required

    Chlorine gas by electrolysis with

    hydrochloric acid solution:

    Manufactured on site through

    electrolytic reaction with hydroch-

    loric acid (HCl)

    Electrolysis products are chlorine

    gas and hydrogen

    3.3 kg (12.5 gal) of 33 % hydroch-

    loric acid and 2-2.5 kWh of elec-

    tricity are required to manufacture

    1 kg (2.2 lb) of chlorine gas


    Produces the same effect as chlo-

    rine gas

    Eliminates chlorine gas bottle

    storage, safer operation.

    Chlorine gas is directly dissolved

    into the pool water return.

    Hydrochloric acid for both electro-

    lysis and pH-neutralization can be

    stored in one large acid storage



    Chlorine detectors and alarm sys-

    tem required.



    Delivered as solid

    Contains both bromine and chlo-


    Strong acid, pH-4


    Active hypobromous acid concen-

    tration remains stable over fluctua-

    tions in pH. At pH - 7.2: 96% ac-

    tive bromine concentration vs 66%

    active chlorine.

    Indoor/outdoor pools/spas can be

    switched over from bromine to

    chlorine for outdoor season.


    Cost 2 to 3 times higher than with chlorine.

    Disinfection slower (slower germ killing velocity) thanchlorine,

    therefore required residual con-

    centrations twice as high as with

    chlorine. Residual HOBr = 2 - 4


    Bromine cannot be stabilized in outdoor pools/spas against UVde-


    Bromine pools must be breakpoint chlorinated more often thanwith

    chlorine to eliminate algae growth

    and organic contaminants.

    Halomethane concentration in pool water higher with bromineas

    compared to chlorine.

    3. Pool Water Distribution and Over

    Overflow Rim/Gutter Arrange-


    The best water treatment systems are of

    little use when the pool water distribu-

    tion system functions unsatisfactorily.

    A perfect water distribution system will

    provide an even distribution of the

    treated water within 5-8 minutes. In

    addition to proper pool water return

    distribution, an even, simultaneous

    overflow at the pool surface water is

    also necessary. In order to achieve

    optimal surface water quality with low-

    er impurity concentrations, modern

    pools are provided with and balanced

    for 100 % pool water overflow at the

    overflow rim/gutter.

    Existing pools under consideration for

    renovation should be provided with 100

    % pool water overflow systems when-

    ever possible.

    Figures 2 and 9 show how the pool

    water return distribution and overflow

    rim/gutter can be renovated to provide

    a better cleaning effect at the pool wa-

    ter surface. The pool water return is

    delivered through low-lying nozzles

    located on the pool walls (horizontal

    distribution) with 100 % of the surface

    water flowing over the rim/gutter and

    into the collection channel. The col-

    lected pool water is then channeled

    directly back to the balance tank.

    Reusing existing floor outlets is also

    possible when dye tests indicate ac-

    ceptable distribution and mixing.

    4. Sizing the Water Treatment


    The calculation of the water circulation

    capacity of a public swimming pool is

    of significant importance for good wa-

    ter quality.

    In the United States the water flow rate

    through a pool is based on turnover

    rate, which is the number of hours to

    circulate the pool water volume one

    time. This method does not account for

    higher impurity concentrations at the

    pool water surface, bather frequency or

    the specific loading capacity of the

    water treatment process. Two frequent-

    ly used public pool water treatment

    standards are the National Spa and Pool

    Institute (NSPI) and the American Pub-

    lic Health Association (APHA) stan-

    dards. The required pool water circula-

    tion rates are shown below:


    © Reproduction is Prohibited, 1995.

    NSPI = Turnover of 8 [1 volume/8


    APHA = Turnover of 6 [1 vo-

    lume/6 hours]

    The German, Swiss and Austrian, as

    well as many other northern European

    pool water quality standards, incorpo-

    rate bather loading and pool water sur-

    face area and the water treatment

    process into the calculation.

    The calculation for sizing the water

    circulation rate in accordance with the

    German Standard DIN 19643 is as


    V = A x n / a x b [m3/h]


    V = water flow rate of the treated water

    (pool water return) [m3/h]

    A = water surface area of the pool [m2]

    a = water surface area per person [m2]

    n = specific bather frequency per per-

    son [1/h]

    b = specific loading capacity per person


    The appropriate values for "n" and "a"

    according to the DIN standard are

    shown below:

    as given previously by equation (1),

    then if a water treatment process is

    used with b=0.5, each person should

    have 2.0 m3 (530 gal) of treated water

    volume available in which to bathe. (P

    = 1 person).

    There are, however, special cases,

    which require closer consideration:

    Wading/ Children’s attraction pools

    Warm massage/attraction pools

    Water sides

    Thermal/Mineral pools

    Hot Whirlpools

    5. Improvement of the Water Quality

    Even if no complaints about pool water

    hygiene are made, improvements can

    be made to increase bather comfort.

    An improvement of the water treatment

    is frequently found when the fresh wa-

    ter intake can be reduced. Inadequate

    water quality can be the result of prob-

    lems with the system due to higher

    bather loads than the system is able to

    handle. These problems exist, for ex-

    ample, when the following has oc-


    Subsequent construction on site

    Construction of additional attrac-tions

    Increase of the water temperature setpoint.

    Pools which are not designed for high bather loads and must beadjusted

    later to meet the latest operational re-

    quirements. For example, with hot

    whirlpools and massage pools or chil-

    drens’ areas.

    The following parameters indicate

    a need for improvement of the

    pool water treatment system:

    Burning sensation in the eyes

    Higher concentration of combined chlorine

    Higher portion of the oxidiz-ing chemicals, which is

    measured as the potassium

    permanganate (KMnO4) con-

    sumption, over 3 mg/liter


    Urine (NH3) concentration, over 1 mg/liter


    Under such conditions a remedy is

    to control the total chemical

    treatment system and to adjust the

    entire water balance. The procedure in

    such cases is represented by the follow-

    ing check list:

    CChheecckk LLiisstt ffoorr tthhee PPrroocceedduurree ffoorrOOppttii--

    mmiizziinngg tthhee WWaatteerr TTrreeaattmmeenntt

    1. Analysis of the Existing Conditions

    Determination of the load

    Fresh water consumption

    Measured water circulation capac-ity

    Necessary circulation capacity

    KMnO4 consumption before and after the sand filter

    Evaluation of the chemical and bacteriological analysis

    2. Causes of Improper Operation

    (things to look for)

    Proper operation of the pressu-rized sand filter

    Swimming filter, change filter media, injection correction,

    change activated charcoal

    Test the injection

    Observe the operation

    Analyze the operation procedure

    3. Operation Manual for Optimization of the Existing System

    Correcting the established defect

    Optimization of system operation

    Repeated measurements

    4. System Completion

    System completion: Planning for additional installations

    5. Commissioning

    Testing for improved water quality with reductions in freshwater


    Development of a carefully planned inspection table for de-

    tailed analysis of the entire system

    It is necessary to consider, after the

    detailed analysis of the improvements

    to the water treatment system, whether

    the water circulation rate should be

    increases or whether it is meaningful to

    develop a more intensive treatment


    The graph shown in Figure 13 shows

    and example of this problem. (See fig-

    ure 13)

    Type of


    Pool Depth





    n [1/h]




    a [1/m2]

    Diver Pool


    ( 11.0 ft)



    (48 sf)



    > 1.35

    (> 4.5 ft)



    (48 sf)




    0.6 to 1.35

    (2 to 4.5 ft)



    (30 sf)



    **** V = 2 turnovers/h ****

    (Turnover = 0.5)


    b = P/V [1/m3]


    © Reproduction is Prohibited, 1995.

    The curve shows the concentration of

    dirt in the rim/gutter overflow water as

    a function of the pool water circulation

    rate. The dashed lines represent possi-

    ble water conditions in the pool, once

    with a lower circulation rate of 33 m3/h

    (145 gpm) and once with a higher rate

    of 100 m3/h (440 gpm). The dashed

    parallel lines represent shifts in water

    quality using a more intensive water

    treatment process. It is generally true

    that greater improvements in water

    quality can be achieved by providing

    higher pool water circulation rates, than

    with the costlier methods associated

    with improving the water treatment


    The results of this graph can be record-

    ed and verified by measuring the con-

    centration of oxidant in pool water is

    indicated and measured by the con-

    sumption of potassium permanganate

    (KMnO4) across the water treatment


    When the circulation rate is increased

    additional filters are usually necessary.

    Improvements to the water treatment

    system capacity can be achieved by

    addition of activated charcoal filters.

    The activated charcoal acts as a separa-

    tion between oxidation and disinfec-

    tion. Where the treatment system can

    be arranged for disinfection with chlo-

    rine or with the ozone/chlorine process.

    A further advantage of the installation

    of activated charcoal filters exists by

    the reduction of chloroform byproduct.

    The Federal Health Office in Berlin,

    Germany has studied the use of acti-

    vated charcoal powder injection before

    the sand filter for use in hot whirlpool

    applications with very favorable re-


    Further possibilities for the improve-

    ment of water treatment processes exist

    by installation of equipment to reduce

    the concentration of combined chlorine

    either by innovative use of activated

    charcoal or by UV-radiation.

    EExxaammpplleess ooff IInnssuuffffiicciieenntt WWaatteerrQQuuaalliittyy

    The temperature of the wad-ing/children’s attraction poolhas

    been raised. Additional attractions

    were built, whereby loading at the

    filters substantially increased and

    is overloading the water treatment


    Corrective measures:

    Daily backwash

    Change Floculant and/or increase injection rate

    Increase fresh water intake

    Addition or improvement of a foot wash pool

    Raise chlorine concentration from 0.3 mg/l (ppm) to 0.5 mg/l(ppm)

    (Subject to local code)

    6. Optimization of Energy Savings

    A frequent goal of most renovation and

    improvement projects for water treat-

    ment systems is reduction of operating


    6.1 Pool Water Heating

    Outdoor pools can be heated with sun

    absorbers. The required absorber sur-

    face is approximately 50% of the pool

    water surface area. If a solar absorber

    is not possible, because of limited free

    area for construction, then a heat pump

    should be recommended. Heating out-

    door pools with oil or gas is usually no

    longer considered.

    Indoor pools can be heated by the heat

    of rejection from a dehumidification

    heat pump in the ventilation unit, the

    waste heat from considering boiler

    exhaust gas or by geothermal heat

    pump systems.

    6.2 Heat Recovery

    The heat recovery from the constant

    pool water effluent offset by the fresh

    water intake can be economically re-

    covered in indoor swimming pools.

    The efficiency of the heat exchanger

    process using a shell and tube or plate

    frame heat exchanger is between 85

    and 90%. This process uses no addi-

    tional electric energy for the heat trans-

    fer between the warm effluent and cool

    fresh water.

    The fresh water can be heated up to

    between 2 and 4 F of the pool water

    temperature reducing the fresh water

    intake heating load considerably.

    The plate frame heat exchanger usually

    has a simple payback period of 2 years.

    In addition a waste water heat recovery

    unit, incorporating both recuperative

    heat exchange as well as heat pump

    technology, can be installed. These

    systems are self-cleaning and usually

    pay for themselves within 6 years.

    6.3 Electrical Energy

    During night setback operation main

    circulating pumps can be switched-off

    saving energy. Therefore, it is recom-

    mended to equip each water treatment

    system with a minimum of two circu-

    lating pumps, whereby reduction of the

    water flow rate is possible. Leaving

    one of two pumps piped in parallel in

    operation provides approximately 70%

    of the circulation capacity

    while saving 75% of the unoccupied


    © Reproduction is Prohibited, 1995.

    mode pumping energy. (Applicability

    is dependent on the resulting pool water

    quality, however, is usually not a prob-


    In indoor swimming pools with long

    operating hours the under water light-

    ing system can have a significant influ-

    ence on the electrical energy and oper-

    ating costs. A 25-meter, 8 lane pool

    could have a $5,000 per year difference

    in operating cost by lighting the pool

    during the day. (Electricity cost, lamp

    replacement cost and labor costs). It is

    always recommended to provide ade-

    quate daylighting and reduce the oper-

    ating time of the underwater lighting


    Adequate lighting during the day is

    necessary to improve pool use safety.

    6.4 Fresh Water Consumption

    The fresh water consumption in a

    swimming pool is dependent upon the

    number of visitors to the facility. In

    indoor swimming pools the entrance

    counter sales are the measure of the

    number of visitors and can also be used

    to adjust the fresh water intake.

    In outdoor pools the entrance counter

    sales are not as reliable because the

    visitors come and go as they please

    over the course of the day. A good

    value to use is twice the number of

    counter sales. The best method for

    estimating the number of visitors and

    therefore, balancing the fresh water

    intake, is by counting them from time

    to time throughout the day.

    In wading/children’s attraction areas

    the fresh water intake should be calcu-

    lated using a bather frequency of 2, that

    is each child uses the pool twice each

    hour. For example, with an average of

    25 children in the area during the day a

    specific bather frequency of 50 children

    per hour is used. Then if the children’s

    area is open for 8 hours per day, 400

    bathers are used for the fresh water

    intake calculations. Accordingly the

    minimum recommended fresh water

    intake is 400 x 30 l/P = 12 m3/Day =

    0.5 m3/h ( 2 gpm).

    Normally the fresh water intake for

    each pool will be divided during initial

    balancing of the system according to

    the filter capacity (main pool water

    circulation rate). This works because

    the water circulation rate for each pool

    connected on one filter system has been

    sized for the expected loading at that

    particular pool.

    During operation variations in water

    quality between pools on the same filter

    (water treatment) system may be de-

    tected, and at this time a correction of

    the fresh water distribution to be differ-

    ent pools is necessary.

    6.5 Automatic Control and Regula-tions

    Modern public swimming pools are

    equipped with direct digital control

    (DDC) systems. The house energy

    management system (EMS) is usually

    capable of controlling and managing

    operation schedules for many building

    components in addition to the pool

    water treatment systems. These com-

    ponents, whether mechanical or elec-

    trical, are initially balanced and pro-

    grammed during system start-up


    It is important to adjust all automatical-

    ly controlled equipment for economical

    optimization of operation. Water

    treatment systems can be adjusted to

    minimize electrical energy consump-

    tion of electricity driven motors as well

    as by limiting backwash schedules

    through time valuing by programming

    proper operational schedules.

    Other water treatment equipment have

    integral stand-alone controls and must

    be adjusted individually, such as pH-

    neutralization and disinfection set-

    points. These components can only be

    optimized to minimize chemical usage

    if accurate log sheets are maintained by

    operating personnel which can be used

    by engineers and technicians to under-

    stand how the systems are being oper-

    ated. Log sheets can be obtained by

    contacting B2E Consulting Engineers,

    Leesburg, VA.

    7. Final Remarks

    It has been shown that to improve the

    water treatment process an examination

    of all of the appending components and

    their combined effects is necessary.

    Experience shows that the following

    list recognizes problems which occur in

    many installations:

    Examples of Common Problems:

    Automatic pool water balance regulation system test probewa-

    ter removal near the floor or from

    main drain piping.

    Automatic pool water balance regulation system test probewa-

    ter removal position next to a

    massage jet.

    Automatic pool water balance regulation system test probewa-

    ter removed from an unloaded

    area of the pool.

    Regulation ineffective because the chlorine injection systemca-

    pacity is undersized.

    Fresh water intake and disinfec-tant injection improperlycalcu-


    Back pressure in the filter back-wash drain which inhibitsan

    even backwash across the filter


    Undersized backwash fluidiza-tion air compressor which isuna-

    ble to generate proper fluidiza-

    tion of the filter media.

    Filter short-circuiting from clogged and calcified filtermedia

    (sand filter).

    Increased acid consumption from various causes, such asincreased

    evaporation at water attractions

    or high heat exchanger surface


    Germ growth in the activated charcoal, primarily due to low

    chlorination in the backwash wa-


    8. Bibliography

    * Beddow, B., 1995. Planning, Construction and Operation of

    Whirlpools, Leesburg, VA.

    Beddow, B., 1995. Ventilation in Natatoria, Leesburg, VA.

    * Deutsches Institut für Normung (DIN 19643), 1993.

    Aufbereitung von Schwimmund

    Badebeckenwasser. Berlin,


    Eichelsdorfer, D. Jandik, J., Weil, L. Volume 5, 1981. Bildungund

    Vorkommen von organischen

    Halogenverbindung im

    Schwimmbeckenwasser. Archiv

    des Badewesens. Wiesbaden,


    * Herschman, W., 1980. Aufbereitung von


    © Reproduction is Prohibited, 1995.

    Schwimmbadwasser. Krammer-

    Verlag. Düsseldorf, Germany.

    Kannewischer, B. Volume 1, 1993. Badewasserdes infection

    mit Chlorgas und mögliche

    Alternativen. Umwelttechnik.

    Zürich, Switzerland.

    Kannewischer, B., 1988. Optimieruug der

    Wasseraufbereitung in

    öffentlichen Hallen – und

    Freibädern, Umwelttechnik. Aug


    Kannewischer, B., 1979. Badewasseraufbereitung für

    öffentliche Bäder. BAG Brunner

    Verlag. Zurich, Switzerland.

    Kurzmann, A., 1978. Schwimmbeckenwasser

    aufbereitung mit oder ohne Ozon.

    Beratungsbüro und

    Laboratorium für Ozon - und

    Wasser - Technologie. Walldorf,


    McGregor, R., Walenczak, W., Rogers, R., Magnetti, L. Volume

    2, 1993. Case Study: Ozone-

    Based Water Treatment for High

    - Quality Air and Water in a Mu-

    nicipal Swimming Center. Pro-

    ceedings: Eleventh Ozone World

    Congress. San Francisco, CA.

    Mood, E.W., 1981. Public Swimming Pools: Recommend-

    ed Regulations for Design and

    Construction, Operation and

    Maintenance. American Public

    Health Association. Washington,


    Pacik, D. Volume 4, 1992. Trihalogenmethanein neues

    Problem? Archiv des

    Badewesens. Wiesbaden,


    Pitrak, P.J., Rennell, D.S. Second Edition, 1992. Basic

    Pool & Spa Technology. Na-

    tional Spa and Pool Institute.

    Alexandria, VA.

    Primarvesi, C.A., Althaus, M., 1980. Wert Bestimmung für das


    durchgeführt durch das Hygiene-

    Institute des Ruhrgebiets,

    Gelsenkirchen. Hygiene-Institute.

    Gelsenkirchen. Germany.

    Roeske, W., 1980. Schwimmbeckenwasser

    Anforderungen – Aufbereitung –

    Untersrchung; Verlag otto Haase,

    Lübeck, Germany.

    Saun, C., 1989. Planung von Schwimmbä dern, Bau und

    Betricb von privaten und

    öffentlichen Hallen – Sowie

    Freibäern einschlie Blich

    Whirlpools and Medizinische

    Bäder, Krammer – Verlag,

    Düsseldorf, Germany

Bruce E. Beddow, P.E. Harald Kannewischer, dipl. Ing.Normen (DIN) 19643 Treatment and Disinfection of Water for Bathing Wa-ter, and the Swiss, Schweizerischer Ingenieur und Architekten-Verein - [PDF Document] (2024)
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