The Adenosine Triphosphate (ATP) technology can be used as a measurement of the total living biomass. However, care must be exercised in its application and its interpretation. The use of this technique on samples from cooling water systems clearly indicate that there are three distinct pools of ATP, classified as bacterial ATP, free ATP and total ATP, the latter being the sum of the free ATP and bacterial ATP. The mode of action of certain biocidal agents is by disruption of cell membranes, a process which does not decrease the pool of total ATP, but does move ATP from the bacterial ATP pool to the free ATP pool. As a consequence, it is important that for a realistic interpretation to be made, it is necessary to know which biocidal agents are being used and to fully understand their mode of action.
Keywords: ATP (Adenosine Triphosphate), free ATP, biological control, biocides, open recirculating cooling system.