A colony of 50 people is served by a septic tank. The rate of water supply is 90 lpcd in the colony and 40% of it is going to the septic tank. The retention period of the tank

Q. A colony of 50 people is served by a septic tank. The rate of water supply is 90 lpcd in the colony and 40% of it is going to the septic tank. The retention period of the tank is 24 hours. The length of the septic tank is___________________meter (rounded off to two decimal places).

Assume, storage capacity/person = 0.085m³ (3 years) Space for digestion = 0.0425 m³/person

Depth of tank = 1.4 m Length: Width = 2:1

A. 34.2

B. 3.42

C. 342

D. 0.342

Ans: 3.42

Water in septic tank = 50 × 90 × 1 × 0.4 = 1.8 cu. m (40% of total consumption)

Storage volume of septic tank = 0.085 × 50 = 4.25 cu. m

Digestion volume of septic tank = 0.0425 × 50 = 2.125 cu. m

Total volume = 1.8 + 4.25 + 2.125 = 8.175 cu. M