Study on the hygienic safety of point-of-entry treatment devices finished
Within the European standardization and especially during the development of the European Acceptance Scheme the German standards for treatment devices will be under discussion.
To guarantee that the high hygienic quality level of these devices can be held for Europe it was necessary to evaluate the experiences with DIN 19636 (water softeners) under a microbiological point of view. Moreover, a literature study and an evaluation of case studies were necessary to check the relevance of the possibility of a microbial contamination of water softeners. A microbial contamination may lead to growth of potentially pathogenic bacteria in these devices, representing a permanent threat to the consumers" health.
The phenomenon of bacterial growth in water softeners is well known for years. In the 1980s a German DIN Standard 19636 for water softeners was developed to guarantee the hygienic safety of consumers. The DIN Standard 19636 assures on the one hand that the distribution system is not contaminated by these devices and on the other hand that the drinking water used in the household still meets the microbiological quality according to the German drinking water guidelines (HPC below 100 CFU/mL). Moreover, the DIN standard 19636 specifies to test the disinfection effi-ciency of a softener during the regeneration phase, after being contaminated with Pseudomonas aeruginosa. This is possible by sanitizing the resin bed by chlorine production during regeneration.
Pseudomonas aeruginosa is used as an indicator for potentially pathogenic bacteria being able to grow also in low nutrient conditions which normally prevail in drinking water. Like HPC, also the numbers of Pseudomonas aeruginosa increase rapidly as soon as stagnation occurs.
The results of 10 years (1992-2001) of testing water softeners according to DIN 19636 show, that it is possible to produce water softeners that comply with that stan-dard. In this period, 24 different models were tested from which 17 were accepted. Also from those which were accepted about 53% (HPC) respectively 63% (Pseu-domonas aeruginosa) did not fulfill the criteria on the first run.
Of course, Pseudomonas aeruginosa is normally not present in the distributed drinking water. But under certain conditions Pseudomonas aeruginosa can be introduced into the drinking water distribution system, for instance during construction work. The occurrence of Pseudomonas aeruginosa was shown in different cases in treatment plants, public drinking water systems and in house installations.
The compliance with DIN 19636 guarantees, that a water softener will not be a constant source of contamination, even if it is once inoculated with a potentially pathogenic bacterium like Pseudomonas aeruginosa.
