Problem 9.7: After adding a biodispersant to a cooling

From Chapter 9 Problem Set. Level 2: Applied Thinking.

Question

After adding a biodispersant to a cooling tower, turbidity spikes from 15 to 50 NTU and the ATP reading in the bulk water triples. The operator wants to stop the dispersant because “it made things worse.” Explain what is actually happening and whether this is a problem or a success.

Answer

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The dispersant is working. The turbidity spike and increased ATP in bulk water indicate that the biodispersant is lifting biofilm material from pipe and fill surfaces into the water column - material that was previously hidden from both monitoring and treatment. The “worse” numbers reflect what was already present on the surfaces but invisible to bulk water testing. This is a success: the shelter has been disrupted and the previously protected organisms are now exposed to the biocide program. The correct next step is to follow the dispersant application with a biocide treatment to kill the newly exposed organisms, and to increase blowdown or filtration to remove the suspended biological material from the system.