GATE CE 2016 Set 2 — Question 29
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Environmental Engineering → Drinking Water Treatment → Softening
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Question
The hardness of a ground water sample was found to be 420 mg/L as CaCO. A softener containing ion exchange resins was installed to reduce the total hardness to 75 mg/L as CaCO before supplying to 4 households. Each household gets treated water at a rate of 540 L/day. If the efficiency of the softener is 100%, the bypass flow rate (expressed in L/day) is _________
Correct answer
380 to 390
Solution
Total water demand for 4 households is calculated as:
Given:
Applying the mass balance for hardness:
The bypass flow rate is approximately 385.71 L/day, which falls within the specified range of 380 to 390.
Given:
- Initial hardness () = 420 mg/L as CaCO
- Desired final hardness () = 75 mg/L as CaCO
- Softener efficiency = 100%, so hardness of softened water () = 0 mg/L
Applying the mass balance for hardness:
The bypass flow rate is approximately 385.71 L/day, which falls within the specified range of 380 to 390.
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