# Environmental Engineering Questions and Answers – Slow Sand Filter

This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Slow Sand Filter”.

1. The depth of an enclosed tank of a slow sand filter lies in the range of ______
a) 1-2m
b) 2.5-4m
c) 2-5m
d) 3-5m

Explanation: The depth of an enclosed tank of a slow sand filter lies in the range of 2.5-4m and its surface area lies between 50-1000m2.

2. When the fineness of sand increases __________
a) The bacterial efficiency increases
b) The rate of filtration increases
c) The rate of filtration first decrease, then increase
d) The bacterial efficiency remains constant

Explanation: When the fineness of sand increases, the bacterial efficiency increases, but rate of filtration decreases. Fine sand is preferred when high bacteria and turbidity removal efficiency is desired.

3. The thickness of the base material on which filter media are supported is __________
a) 10-100cm
b) 20-80cm
c) 30-75cm
d) 10-30cm

Explanation: The base material consists of 30-75 cm thick gravel bed which is laid in layers of 15 cm with finer topmost layer and coarser bottom layer.

4. The minimum number of filter beds in the slow sand filter is __________
a) 1
b) 2
c) 3
d) 3

Explanation: The minimum number of filter beds provided in the slow sand filter is 2 where one unit is provided as stand by for an area of 20m2.

5. The area of the filter is 1500. What is the number of beds to be provided?
a) 1
b) 2
c) 3
d) 6

Explanation: The area of filter is 1500 which lies between 1201-2000m2. So, the number of beds to be provided is 6.

6. The slow sand filter is able to remove ______ % of bacteria in water.
a) 90
b) 95
c) 98-99
d) 100

Explanation: The slow sand filters are highly efficient in the removal of bacteria and can remove around 98-99% of bacteria present in water.

7. The slow sand filter is efficient in removing turbidity of water.
a) True
b) False

Explanation: The slow sand filter is not efficient in removing turbidity of water and is not capable of removing turbidity over 50ppm.

8. The maximum daily demand of a city is 24*105 and the rate of filtration is 100 per litre per hour per m2. What is the area of the filter?
a) 10
b) 100
c) 1000
d) 1500

Explanation: Maximum daily demand = 24*105
Rate of filtration = 100
Area of filter=Maximum daily demand/Rate of filtration=24*105/(100*24)
=1000m2.

9. The slow sand filter is designed for _____________
a) Maximum daily demand
b) Maximum yearly demand
c) Average daily demand
d) Maximum weekly demand

Explanation: The slow sand filter is designed for maximum daily demand, which is 1.8 times the average daily demand.

10. What is the frequency of cleaning of a slow sand filter?
a) 1 week
b) 1-3 months
c) 2-3 days
d) 2-3 weeks

Explanation: The slow sand filter requires cleaning, depending upon the impurities present in water and normally it is done after 1-3 months.

11. What is the maximum filter head up to which slow sand filters are worked upon?
a) 25cm
b) 50cm
c) 75cm
d) 100cm

Explanation: Initially the filter head is only 10-15cm but it increases as suspended matter is arrested. When the filtration head reaches the maximum permissible value of 75cm, the filter requires cleaning.

Sanfoundry Global Education & Learning Series – Environmental Engineering.

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