⟵ 09 Microbiology (Engineering Notes) · Contents · 09 Microbiology (Answer Key) ⟶
Microbiology: Problem Set
“These are only provided to reinforce understanding. The Engineering Notes contain some of the information that will be required. Make sure to employ dimensional analysis for all unit conversions.”
Level 1: Conceptual Mastery
-
In two sentences, explain why biological control requires fundamentally different thinking than scale or corrosion control.
-
A mature biofilm on a condenser tube is treated with a high dose of chlorine. Planktonic counts drop to near zero within 30 minutes. Two days later, counts are back to pre-treatment levels. Explain what happened using the concepts of EPS, diffusion limitation, and survivor repopulation.
-
Using the oxygen differential cell from the Corrosion chapter, explain how a biofilm creates the same corrosion mechanism as a deposit – but sustains it continuously.
-
A cooling tower operates at pH 8.3 with a free chlorine residual of 0.5 mg/L. Using the chlorine/pH table, estimate the percentage of chlorine present as HOCl. Is this adequate for biological control?
Level 2: Applied Thinking
-
A 4-inch branch off a cooling tower recirculation loop has been valved off for 6 months. The water inside is at 85°F. No biocide reaches it. Describe the biological progression you would expect from month 1 through month 6, and explain why this dead leg is a Legionella risk.
-
A facility has used the same non-oxidizing biocide (isothiazolone) on a weekly slug-dose schedule for 18 months. Biological counts have been rising steadily for the last 6 months despite consistent dosing. Explain what is likely happening and propose a modified program.
-
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.
Level 3: System Integration
-
A cooling tower loses its biocide feed pump on Friday. It will not be repaired until Monday. Using the biofilm lifecycle, the amplifier effect from the Suspended Solids chapter, and the condenser free body diagram from the Pillars chapter, describe the likely sequence of events over 72 hours across all four pillars.
-
A hospital cooling tower has excellent bulk water chemistry: chlorine at 0.5 mg/L, conductivity in range, coupons acceptable, no visible scaling. Legionella culture comes back at 1,000 CFU/mL. Explain how this is possible in a “well-treated” system. Identify at least three potential harboring locations.
-
You are treating a cooling tower with no sidestream filtration, inconsistent biocide feed, and visible biofilm on fill media. The customer asks you to “double the biocide.” Write a 4–6 sentence explanation of why this approach alone will not work, and what additional steps are required. Reference access, shelter, and at least one pillar interaction.
Problem notes
Each problem as its own linked note.
9.1 · 9.2 · 9.3 · 9.4 · 9.5 · 9.6 · 9.7 · 9.8 · 9.9 · 9.10
⟵ 09 Microbiology (Engineering Notes) · Contents · 09 Microbiology (Answer Key) ⟶