GATE 2018 CE (CE2) – Question 61
A water-treatment plant has 4 filters with filtration and backwashing rates 200 and 1000 m³/day/m². Backwashing takes 15 min/day, and maturation after cleaning takes 30 min. If water wasted during washing and maturation is recovered, the percentage increase in filtered-water production, to two decimals, is ______%.
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Correct answer: 7.75 to 7.95
Explanation
Per square metre, filtration runs 1425 min/day, producing $200(1425)/1440=197.9167$ m³. Maturation wastes $200(30)/1440=4.1667$ m³; washing uses $1000(15)/1440=10.4167$ m³. Current net production is 183.3333 m³, and recovery is 14.5833 m³. Increase is $100(14.5833)/183.3333=7.9545\%$, rounded to 7.95%.