Miljøprojekt, 1105 – Opstilling af forsøgsprotokol til vurdering af mikrobiel vækst i forbindelse med VA-godkendelse af større vandbehandlingsanlæg

Opstilling af forsøgsprotokol til vurdering af mikrobiel vækst i forbindelse med VA-godkendelse af større vandbehandlingsanlæg

Summary and conclusions

This report includes a detailed protocol on the microbiological testing of water treatment units for which VA godkendelse^[1] is requireda demand prior to introduction to the Danish market of private housing.

The objective of a microbiological test is to document that when used for its purpose, a water treatment units does not cause microbial growth in the unit and thereby affect the microbiological quality of the treated water.

A protocol is designed for cold water units for removal of undesirable matter and/or taste and smell and a protocol is designed for hot water units for removal of Legionella. The protocol for cold water units must furthermore be used for drinking water coolers.

As a starting point the above units will be tested microbiologically for 6 weeks, including inoculation of a cultivated mixture of the bacteria present in the tap water of the installation tested, and regular sampling. The test of the hot water units will furthermore include inoculation with Legionella bacteria. During the entire test period normal consumption will be simulated at the unit including tapping several times a day on working days, and the plants being left idle for short period of times during weekends.

The protocol, which has been tested in practice on 3 separate cold water units and 1 hot water unit, has shown that with the technologies used for water treatment today it is sufficiently flexible and at the same time robust enough for the purpose. The protocol has also been designed for implementation on an accredited microbiological laboratory.

As an acceptance criterion slightly increased numbers of aerobic count are acceptable at the introduction of a water treatment unit, however, max. 5 times higher in the treated drinking water or domestic hot water. This criterion is in line with criteria laid down by international institutions, including NSF and DWI. As another criterion no selection of microorganisms should occur in the units in question when they are used for their purpose. It is therefore a requirement that the CFU at 37 degrees centigrade does not gradually or systematically increase for the 6 weeks of testing, and that there are no signs of any development of a bacterial culture in the cold water units.

In hot water units a reduction of the Legionella bacteria inoculated must be detected.

Fodnoter

^[1] VA godkendelse = approval of Water and Sewage system by Danish authorities.