Problem 10.4: A closed chilled water loop shows brown turbid

From Chapter 10 Problem Set. Level 1: Conceptual Mastery.

Question

A closed chilled water loop shows brown, turbid water at 45 NTU despite having been in operation for two years. Is this a suspended solids problem or something else? What would you investigate first?

Answer

Show answer

In a closed system that has been operating for two years, 45 NTU is a suspended-solids problem, but the source is probably corrosion rather than external dirt. Closed systems are not continuously exposed to atmospheric dust, but they can still accumulate solids from makeup water, construction debris, maintenance activities, process leaks, line breaks, and internal corrosion. In this case, the brown, turbid water most likely indicates iron oxide generated by active corrosion of carbon-steel piping. Investigate first: (a) check the corrosion inhibitor residual: is the treatment program being fed consistently? (b) filter a sample and examine the particulate: brown/red suggests iron oxide, black suggests magnetite or SRB activity, green suggests copper corrosion products. (c) check whether the system was properly flushed after construction: construction debris from two years ago can continue circulating indefinitely.