# A village has a population of 200 with an average rate of water demand as 100 litre per capita per day. A rapid sand filter having an average filtration rate of 100 litre/hour/m2 is to be designed for water treatment. The area of rapid sand filter required is: (Take the ratio of maximum demand to average demand as 1.5)

A village has a population of 200 with an average rate of water demand as 100 litre per capita per day. A rapid sand filter having an average filtration rate of 100 litre/hour/m2 is to be designed for water treatment. The area of rapid sand filter required is: (Take the ratio of maximum demand to average demand as 1.5)

### Right Answer is: 12.50 m2

#### SOLUTION

Filtration is a physical operation that is used for the separation of solids from fluids (liquids or gases). The mixture flows through a porous bed through which only the fluid can pass.

In the plant, rapid sand filters containing relatively coarse sand and other granular media are used to remove the particulate matter. In addition to the particulate matter, it can also remove flocs. Flocs are formed using flocculating agents which are typically salts of aluminum or iron. They have impurities trapped in them.

Given,

Rate of filtration = 100 l/h/m2

Population = 200

Average water demand = 100 l/day/head

Filter bed utilization = 24 h/day

Average daily demand = population × per capita demand = 200 × 100 = 20000 l/day

Maximum daily demand = 1.5 × Average daily demand = 1.5 × 20000l/day =30000l/day

Water demand per hour = 30000 / 24 = 1250  l/h

Total surface area of filters required = Water demand / Rate of filtration

Surface area = (1250) / 100 = 12.5 m2

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