TRANSLATION (PART)

DR. LUDWIG WEIL & DR DEITER EICHELSDÖRFER

The water which is used in swimming and bathing pools has loading of continuously changing types of bathers who put heavy demand upon all parts of the swimming pool water treatment system, since the water has to maintain a high quality standard which obviates infection risks.

For this reason, bathing water in public pools and commercially run ones in Germany, is required to at least equal the microbiological examination standards for drinking water (1), and by so doing, to avoid risk of epidemic. Swimming pool water is subjected to search for Pseudomonas aeruginosa, with search for Legionella pneumophila to be soon included.

As at the present state of scientific and technical understanding, fully satisfactory hygienic quality of swimming and bathing water can be attained only by ensuring that the pool-water circulation circuit section performance is fully co-related, stage by stage, so that each stage of water use and treatment is optimised, thus ensuring the maximum effect of cyclic water treatment and disinfection.

Diagram 1: Flow system for water treatment using flocculation + filtration.

The treatment and disinfection of bathing water is done in distinct and identifiable stages (Diagram 1).

The first treatment stage consists of removal of coarse material in suspension in the water, by a sieve, followed by removal of turbidity and minute colloidal matter from the water by flocculation and filtration.

Soluble and organic matter not removed from the water by filtration involves addition of a stage of oxidation to the flocculated and filtered water, and a strong oxidising agent such as chlorine, sodium hypochlorite, or a mixture of chlorine and chlorine dioxide in the ratio of 10:1 is used.

Where pool water is treated with chlorine or a strong oxidising chlorine combination which has a strong disinfection effect, the treatment stages of oxidation and disinfection can be regarded as together.

Separation of the oxidation and disinfection stages can be accomplished, however, but only by additional technical effort, as may be seen by the example of the treatment sequence of:

Legal specifications for microbiological standards of hygiene demand that the disinfection stage has to operate continuously and in the shortest possible time to kill off or to inactivate micro-organisms in the pool water and in all parts of the swimming pool.

Disinfection standards demand the destruction of 99.99% of Pseudomonas aeruginosa, an organism used as control, within thirty seconds.

This condition obtains in properly treated pool water with a pH-value close to neutral, and a chlorine concentration of only a few tenths of a milligram per litre of Cl2.

For bathing pools operated in the public ownership or private commercial sectors, there is as yet no alternative known for the use of chlorination.

To ensure that disinfection protection exists in the water stretch between pool inlet and outlet, a water disinfection method has to be used which has an adequate reserve effect.

For bacteria kill-time demand and oxidation effect, reserve or residual in-pool effect, for simplicity of analysis and recording, for continuous concentration measurement and for concentration-linked automatic metering, chlorine, or as an alternative, the use of chlorine dioxide in combination with chlorine, are the only currently known treatment methods meeting all demands.

For these reasons, in the West of Germany, swimming pool water is chlorinated, and no substitutes for chlorine as a disinfectant can be used.

A well-known disadvantage of the chlorination of water used for bathing, is the reaction of chlorine with material of human origin, and natural material such as organic matter contained in pool-fill and top-up water, which produce undesirable and unhealthy by-products of the compounds nitrogen chloride and carbon chloride through chemical and physiological reactions (Diagram 2).

N Cl C Cl

Nitro-Chloro- Carbon-Chloro-

Diagram 2: Classified byproducts of chlorine during bathing water treatment and disinfection using chlorine.

The resultant nitrogen chloride compound in the pool water, known generally as "combined chlorine" is the cause of sore eyes and the traditional swimming pool smell.

To minimise these effects, German Standard DIN 19 643 on the Treatment and Disinfection of Swimming and Bathing Water is currently under revision with the intention of providing that in the future, the concentration of combined chlorine should be reduced to a maximum of 0.2 mg/1.

Critical physiological state is the determinant upon presence of chloro-organic and bromo-organic compounds as result of chlorination of water of bromide content.

Several organo-halogen compounds, included chloro and bromo-organic compounds, can appear, and these are not recognisable in bathing or swimming pools either by smell or by eye-irritation (2), yet these have changing and cancerous propensities.

Of particular interest in bathing water, are the organo-halogen compounds, the highly volatile trihalomethane (THM) compounds, chloroform, dichlorbromoform, dibromochloroform and bromoform (which come under haloform-classification), since they come from the pool-water surface into the pool-hall air, and from there involuntarily and unavoidably into the bather respiratory system (3,4).

The concentration of THM in the swimming pool circulation system, and its chemical structure, depends primarily upon the level of concentration of natural and human-source organic contamination in the pool make-up and circulated water, upon the volume of chlorine injected, upon the concentration of chlorine in the water following injection of chlorine, upon the bromide concentration in the make-up water or bathing water, and upon characteristics of the particular water treatment system used. (5,6).

Of particular importance is the interference effect of natural matter in fill and make-up water, and in particular that of alkali-soluble organic substances derived from decaying vegetable matter. It is for these reasons, that bathing pools which have similar bather-attendance loading and water treatment plant and procedures, can show quite marked difference, because of (THM) effects.

Production of trihalomethane, (THM), by chlorine and organic matter happens much less in water in the pool, than in the water treatment plants.

(THM) production can be expected in areas of highest chlorine concentration, as for example, the point of injection of chlorine into the circulating water, the dosing point for introduction of chlorine solution to the pool water, and in the water-flow line between the chlorine injection point and the pool inlet.

Areas of high concentration of organic interference material also cause production of trihalomethane.

For this reason, the organic material retained in the sand filter, under attack by unused chlorine returning from the pool, also gives rise to the production of trihalomethane.

Between 80 and 90 percent of the byproducts in the pool-hall air, which result from chlorination of swimming pool water in covered swimming pools, is trihalomethane (THM).

In many cases, the trihalomethane concentration can be several hundred micrograms per cubic metre of air, and an instance is known where a concentration of one thousand micrograms of trihalomethane per cubic metre of swimming pool air was recorded.

There is as yet no concrete proof of danger to health to bring about a conclusive assessment of risk, but when chlorofom and other trihalomethanes are in bathing pool water and in the air of covered swimming pools, the presence of these (THM) with all other organohalogen-compounds has to be regarded with acute apprehension and be considered as user-unfriendly and highly undesirable.

Currently, Standard DIN 19 643 is being revised, and it looks as though for the first time there will soon be a limitation of haloform concentration in bathing water down to a maximum of ten micrograms per litre.

There is no doubt that Authorities and commercial concerns will in the future have to ensure that there water analysis laboratories pay particular attention to the analysis and presence of highly volatile organohalogen compounds.

Organic compounds, capable of production of (THM) in presence of chlorine or bromine, come often from quite natural sources, and can appear in water supplies, and in the public water supply.

These waters frequently contain fundamental substances, alkali-soluble organic substances derived from decaying vegetable matter, and higher molecular substances of biogenic origin, for example from moorland earth and earth rich in fundamental substances, the content of which may not be exactly known. Depending upon matrix and molecule size, the substances may be colloidal or go into solution in the supply water.

Tests of chlorine reaction, for example with acid solutions of fundamental matter have shown a variety of results. It has appeared that acid fundamental matter and other fundamental matter of different origins, has shown differing (THM) production characteristics, so that in any individual case, without prior knowledge of nature and surroundings no prediction of reaction can be made.

Important factors are the fundamental substances in he supply water, organic matter and matter of human origin and the largely indeterminate structure of trihalomethane.

Impurities introduced by bathers comes from washing of the skin surface and removal of water-soluble matter out of the skin, as well as by urination and material from the nasal passages.

The appearance that swimming pool water which is treated by chlorine, can also produce (THM), can be traced back to a large or small bromide content in the supply water.

Bromide exists quite naturally in many waters, and can expect to be found in sea and mineral source waters, but traces can also be found in many public supply waters.

Production of chloro- and bromo-trihalomethane in bathing waters containing bromide is illustrated below:

Chlorine + Bromide + THM-indication

Chloro-Bromo-Trihalomethane

The commonly accepted production of bromo - (THM), even with trace-existence of bromide in one milligram per litre Br. and in lesser concentration, has been explained to be due, that to begin with, bromide ions already in the water were oxidised to bromine through effect of chlorine. The bromine thus formed along with chlorine reacted with the trihalomethane existing to form chloroform (CHC13), bromoform (CHr3), or chloro-bromo-trihalomethane dichlorbrommethane (CHC12Br) and dibromchloromethane (CHBr2C1), so that trihalomethane with chlorine and bromine atoms existed in the same molecule (Direct forming).

Chemical reaction (7) shows an indirect means of formation of bromo-trihalogenmethane through over-chlorination of the produced trihalomethane in volume comparable to that of chlororoform.

This indirect method of production, which can be taken as a reaction of chloroform with bromide ions, comes from the primary chloroform, which changes to trichloromethylanion and ends up as dichlorcarbon, as shown:

_ H_

k2

Since chlorine is capable of forming a higher concentration in solution with water than bromine, and is therefore less reactive, the electrophilic dichlorcarbon reacts with the nucleophilic bromide to form bromo-trihalogenmethane:

The production of bromo-trihalogenmethane, can be done using an intermedially changed dihalogencarbon, as shown:

The trihalogenmethyl - anion so produced is more stable than the original, because the brom-atom, to accommodate its negative ions, offers its ‘d’-orbit for use. In the same reaction process, a further exchange of chlorine and bromine atoms can be done.

Trihalogenmethylanion reaction with a proton results in production of trihalogenmethane.

In this way the sequence of change is chloroform, trihalogenmethane, bromine atom, molecule.

The direct and indirect ways of production should not be regarded as separate, but they run parallel to one another, only at differing speeds. Whichever way happens in any particular case, depends upon the characteristics of the water, and upon the chlorine reaction with what is in the water.

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The taking of samples for THMs is a task that should be carefully considered. Liaison with the Analyst is critical as is the analytical procedure for the testing.

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