17-12: Current Microbiological Control Techniques in Cooling Tower Water System

Due to the recent out breaks of Legionnaires Disease such as in New York City it was decided to investigate how and why this could have occurred by cooling tower water systems that were chemically treated. Cooling tower water systems are normally treated by the traditional method of applying microbiocides and often monitored with traditional total bacteria monitoring methods. This has prompted a detailed review of the traditional microbiological treatment applications in numerous cooling tower water systems in all types of industry systems to see if there are any reasons that Legionella Bacteria could still be present. The review showed that traditional microbiological control techniques might be incorrect and misleading in controlling Legionella Bacteria due to the way the microbiocides are being applied. Examples are provided that identify what was found in numerous cooling tower water systems. They show some very interesting and revealing information in that the biocides are applied based on the use of microbiological monitoring such as with “dip” slides or ATP tests which may not control Legionella Bacteria. It also shows that the traditional monitoring of total bacteria that has indicated good microbiological control as reported by culture or “dip” slides maybe incorrect and that the guide lines by CTI and others that ten to the 4th or less is good microbiological control is actually incorrect. This study and the results suggest new application and monitoring methods should be adopted.