Since 1976, Austria has had a Bäderhygienegesetzt (BHyg G, Bathing Hygiene Act), which is the basis for providing perfect water quality in all public swimming pools. This makes Austria one of the few countries in the world to regulate hygiene in this area by law.
Efforts of this kind have also been made in Germany, but despite several attempts, no political consensus for a legal regulation has been found to date. Although there is the Infections-Schutzgesetz (IfSG, Infection Protection Act) with relatively general wording and a recommendation of the Bundesumweltamt (UBA, Federal Environment Agency), concrete framework conditions are only defined in a technical guideline of the Deutsche Industrie Norm - DIN (German Industry Standard) 19 643. Technical progress is now developing continuously, naturally also in process engineering, i.e. water treatment. This process must be taken into account within the framework of the generally recognised rules of technology. This is done by means of a cyclical inventory of the defined framework conditions and, where necessary or appropriate, supplementing and/or new processes, for example ultrafiltration in the DIN.
For this reason, the Bäderhygieneverordnung (Bathroom Hygiene Ordinance) came into force on 1 October 2012 in order to achieve a meaningful adaptation to the current state of science and technology. The same aim applies to DIN 19643, Parts 1-4, as of November 2012, which was published almost simultaneously. It is interesting to compare the two sets of regulations across national borders. This is best achieved by comparing the most important chemical and physical requirements for pool water quality.
Without wanting to discuss agreements or deviations in detail, it can generally be said that both the Bäderhygieneverordnung (Bathroom Hygiene Ordinance) and the DIN have a leading position worldwide in comparison with most other countries and meet high demands on the quality of swimming and bathing pool water. This statement is confirmed, among others, by the defined pH ranges and the low guideline and limit values for the most frequently used disinfectant and oxidising agent, chlorine. As a consequence, both the measuring, control and dosing technology and the individual analysis within the scope of self-monitoring are required with a high level of detection accuracy. Using the example of the individual analysis, the following instructions are given for the exact analysis of a representative water sample.
Advices for the precise analysis of pool water in the individual analysis
The Bäderhygieneverordnung (BHyg V, Bathroom Hygiene Ordinance) in Austria (A) and DIN 19 643 in Germany (D) appeared in 2012 and form the basis for the operation and monitoring of public swimming pools. In order to maintain impeccable hygienic and chemical conditions, it is essential that microbiological, physical and chemical auxiliary hygiene parameters are maintained under all operating conditions. For this reason, the operator of a public pool is obliged to carry out self-monitoring as part of traffic safety and must keep an operating journal of the measured data. The following information on the correct use of individual analysis systems and reagents refers explicitly to Lovibond®, but the basic statements can also be adapted to other equipment systems. The task of the individual analysis systems is to check the measuring and control devices installed in the bath for their detection accuracy and perfect functioning, and to determine the water quality in the pool on the basis of the chemical hygiene auxiliary parameters of free, combined total chlorine and the pH value.
Tablet reagents or liquid reagents?
The answer to this question has an almost philosophical character and often leads to controversial discussions. In principle, one obtains consistent results with both dosage forms within the tolerance of the DPD method (diethyl-p-phenylenediamine) if the correct procedure is followed. The basis for the DPD method is the reference procedure DIN EN ISO 7393-2 (Water-Quality-Determination of free chlorine and total chlorine - Colorimetric method). Tablet reagents have the advantage that they are fresh until they are removed from the undamaged aluminium push-through packaging. DPD No. 1 and DPD No. 3 tablets must have a white surface. Grey or brown speckles on the surface indicate premature ageing due to the chemical reaction with atmospheric oxygen and humidity. These tablets are no longer suitable for analysis and must be discarded. Each tablet contains the optimum reagent dosage. The DPD No. 1 tablet contains both the reagent and the pH buffer to adjust the 10 ml water sample to a pH between 6.2 and 6.5. Only in this pH range does the colour development run optimally. Tablet reagents are not subject to special storage conditions. It is quite sufficient to store them under normal environmental conditions. The guaranteed minimum shelf life is ten years from the date of manufacture. Thus tablet reagents, individually sealed in aluminium push-through packaging, are the ideal form for on-site analysis.
The DPD liquid reagents available on the market do not generally comply with DIN EN ISO 7393-2. They are "stabilised" by the suppliers on the market in order to guarantee use over a longer period of time. Shelf life specifications of between twelve and 24 months are usual, but only if the reagents are stored optimally. Since liquid reagents age very quickly under sunlight or heat (e.g. storage on a radiator), regardless of the manufacturer, it is recommended that they be stored under refrigerator conditions at approx. +6 ℃ to +10 ℃ when not in use. In contrast to the DPD No. 1 tablet, two bottles with different contents are required to determine free chlorine. The first bottle contains the buffer for adjusting the pH value of the water sample, the second bottle contains the DPD No. 1 reagent. Both have to be stored separately because they react with each other in liquid form and would be unusable for analysis within a very short time. Important for the sample preparation is the sequence of reagent addition as well as the exact number and uniform size of the drops. After use, the bottles must be closed immediately with the corresponding lids, as otherwise contact with atmospheric oxygen and humidity and premature ageing may occur. The lids must not be mixed up to avoid contamination of the indicators.
With the DPD No. 1 tablet, the free chlorine is first determined: A clean cell is rinsed with the water to be analysed. A few drops are left in the cuvette. Add one DPD No. 1 tablet and crush the tablet using a clean stirring rod. Fill the vial to the 10 ml mark, replace the cap, swirl several times to mix the contents and swirl several times to mix the contents. Using the DPD No. 3 tablet, determine the total chlorine content. After determining the measurement result (free chlorine), add one DPD No. 3 tablet to the already coloured sample, crush the tablet using a clean stirring rod, replace the cap, swirl the sample to mix and read the result 2 minutes after addition of the DPD No. 3 tablet (total chlorine). Subtracting the value for free chlorine from the total chlorine gives the content of combined chlorine.
The DPD No. 3 tablet contains potassium iodide, which enables the total chlorine to be determined even in the smallest concentration. For this reason, it is absolutely necessary to thoroughly clean the cell, the lid and the stirring rod under tap water after determining the total chlorine. If no attention is paid to this procedure, traces of potassium iodide - DPD No. 3 - may appear to be present when free chlorine is subsequently measured in the same cell. In other words, one involuntarily measures the total chlorine from the outset and believes it to be free chlorine. The Lovibond® liquid reagents for the determination of free chlorine consist of two components, which are added to the sample drop by drop. Similar to the determination of total chlorine with a tablet, a third component is added in drop form when liquid reagents are used. In addition, make sure that the cuvette used (the same of course applies to the lid and the stirring rod) is free of chlorine consumption. Some household cleaners and dishwashing detergents contain reducing substances. These cause a chlorine depletion in the sample and therefore too low measured values. The simplest way to obtain chlorine-depleting cells is to store them in water containing chlorine when not in use. Before use, they are then simply rinsed several times with the sample.
pH value measurement
Although electrochemical measurement with a measuring tolerance of maximum +/-0.1 units is mentioned in the regulations, in practice photometric measurement is often carried out with the indicator phenol red. The electrometric determination has the advantage of greater accuracy over the entire range of 0-14 pH, but the disadvantage of regular calibration using technical buffer solutions to compensate for the drift (ageing) of the pH electrode. Modern photometers also achieve an accuracy of +/-0.1 pH units. The disadvantage is that the phenol red indicator can only detect the limited range between pH 6.5-8.4. pH values in the acidic and alkaline range outside of 6.5-8.4 cannot be determined.
This paper is intended to give you advice and suggestions for the proper assessment of swimming and bathing pool water using the most common auxiliary hygiene parameters, the differentiated determination of chlorine and the determination of pH values.