GATE 2016 CE (CE2) – Question 29
The hardness of a ground water sample was found to be 420 mg/L as CaCO3. A softener containing ion exchange resins was installed to reduce the total hardness to 75 mg/L as CaCO3 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 _________
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Correct answer: 380 to 390
Explanation
Total delivered flow is4·540=2160L/day. A100%-efficient softener produces zero-hardness water, so all hardness in the blend comes from bypassed raw water. Hardness balance gives420Qb=75·2160. Thus **Qb=385.71L/day**; the rest must pass through the resin.