⟵ 11 The Pillars of Water Treatment (Engineering Notes) · Contents · 11 The Pillars of Water Treatment (Answer Key) ⟶
The Pillars of Water Treatment: 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
- A cooling tower suddenly shows higher conductivity, higher pH, and weaker oxidant residual. Before adjusting any feed pump, list:
- what may have changed in what enters?
- what may have changed in what leaves?
- what may now be accumulating?
- and what transformations may be occurring faster than before?
- For each of the following components, write one sentence defining the system boundary and two likely inputs and outputs:
- cooling tower basin
- condenser tube
- feedwater tank
- dead leg in a chilled water system
- For each case, identify the primary pillar and the most likely amplifier:
- Deep pitting beneath brown tubercles on mild steel
- White mineral deposit on a warm tube with soft slime beneath it
- Rapid oxidant demand increase after weeks of poor filtration
- Stable bulk chemistry but increasing condenser approach temperature
Level 2: Applied Thinking
- A feedwater tank normally receives 80% condensate return at 180°F and 20% makeup at 65°F. Suddenly the condensate return drops to 35%, while total flow remains unchanged.
Explain qualitatively what happens to:
- feedwater temperature
- conductivity
- dissolved oxygen load
- sulfite demand
Then explain why increasing sulfite feed alone may not solve the problem.
- A condenser tube receives tower water at 4 cycles, pH 8.3, calcium hardness 220 mg/L as CaCO₃ in the makeup, visible suspended solids, and intermittent oxidant feed.
Write a free body diagram that includes:
- system boundary
- inputs
- outputs
- accumulations
- transformations
- likely surface conditions not captured by the bulk water tests
Then identify which pillar you would address first
- A valved-off 4-inch branch line has been stagnant for 2 years in a nitrite-treated chilled water loop.
Using the four questions, predict:
- what no longer enters,
- what no longer leaves,
- what may have accumulated,
- what chemical and biological transformations likely occurred
Then identify the dominant failure mode.
- A facility reports:
- rising condenser approach
- higher coupon corrosion rates
- higher biocide demand
- visible silt in the tower basin
Use the free body diagram approach to identify the most likely root cause and explain how one problem can create all four symptoms.
Level 3: System Integration
- A cooling tower has high calcium hardness and a phosphate-based corrosion inhibitor. Scale pressure is rising. Lowering pH would help with CaCO₃ control, but may destabilize other parts of the treatment strategy.
Give two alternative responses besides simply feeding more acid. For each, explain the consequences across all four pillars.
- A condenser system shows:
- inhibitor residual on target
- pH in range
- conductivity in range
- biocide schedule maintained
- no visible heavy scale
But corrosion coupons show 6.5 MPY.
Explain at least two ways this can happen using the distinction between bulk-water chemistry and surface conditions.
- Design a 6-step first-visit walkthrough for a cooling tower system using the logic of this chapter. For each stop, state:
- what component you are evaluating
- what you are looking for
- which of the four questions you are answering
- which pillar(s) you are primarily evaluating
Problem notes
Each problem as its own linked note.
11.1 · 11.2 · 11.3 · 11.4 · 11.5 · 11.6 · 11.7 · 11.8 · 11.9 · 11.10
⟵ 11 The Pillars of Water Treatment (Engineering Notes) · Contents · 11 The Pillars of Water Treatment (Answer Key) ⟶