Problem 10.9: A water treater increases the dispersant dose

From Chapter 10 Problem Set. Level 3: System Integration.

Question

A water treater increases the dispersant dose in a heavily fouled cooling tower. Within 48 hours, turbidity increases from 20 to 60 NTU and condenser approach temperature actually improves by 1°F. Explain what is happening and whether this is a problem or a success.

Answer

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The dispersant is working. The turbidity spike from 20 to 60 NTU indicates that the dispersant is lifting deposits from heat-exchange surfaces and piping into the water column. The 1°F improvement in condenser approach temperature confirms this - the insulating deposit layer on the condenser tubes has been partially removed, restoring heat transfer. The “worse” turbidity reading is actually showing material that was already in the system but hidden on surfaces, invisible to bulk water monitoring. This is a success. The correct next steps are to increase blowdown temporarily or ensure sidestream filtration is running to capture the suspended material, and to follow with a biocide treatment to kill organisms that were sheltered beneath the deposits and are now exposed.