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Which of the following statements are correct pertaining to the value of uniformity coefficient Cu for filter sand? (1) For slow sand filters, Cu = 1.8 to 2.5 (2) For rapid sand filters, Cu = 1.3 to 1.7 (3) For slow sand filters, Cu = 1.3 to 1.7 (4) For rapid sand filters, Cu = 1.8 to 2.5

Which of the following statements are correct pertaining to the value of uniformity coefficient Cu for filter sand? (1) For slow sand filters, Cu = 1.8 to 2.5 (2) For rapid sand filters, Cu = 1.3 to 1.7 (3) For slow sand filters, Cu = 1.3 to 1.7 (4) For rapid sand filters, Cu = 1.8 to 2.5 Correct Answer 1 and 2

Explanation:

Slow sand filter and rapid sand filter

 

Slow sand filter

Rapid sand filter

Pre-treatment

Effluents from plain sedimentation coagulation, not req.

Coagulation, flocculation, and sedimentation is a must.

Filter Sand

D10 b/w 0.2 and 0.4 mm

Cu ⇒ 1.8 to 3.

Gravel: 30-75 cm thick

D10 = 0.35 mm - 0.55 mm

Cu = 1.2 to 1.8

Gravel: 60-90 cm thick

Size of each unit

Large such as 30 m × 60 m.

An area from 100 - 2000 m2.

Less flexible on shock loading

Small 5 m × 8 m.

Area < 100 m2

More flexible on shock loading

Rate of filtration

100 to 200 l/hr/m2

3000 to 6000 l/hr/m2

Efficiency

Very efficient in removing bacteria but less efficient in removing colour.

Less efficient in bacteria (80 - 90 %), very efficient in colour removal.

Post-treatment

Disinfection is not a must. Almost pure water obtained.

Turbidity removal up to 50 ppm

Disinfection is a must.

Turbidity up to 35 ppm.

Method of cleaning

Scrapping and removing the top 1.5 to 3 cm thick layer and washing down by hoses.

Backwashing with or without compressed air.

Qty of wash water req.

0.2 to 0.6 % of total filtered water is req. in every 1 to 3 months

A large amount of total filtered water is req. in every 1 to 3 days (1 - 5 %)

Additional InformationPressure filter

The difference between the rapid sand filters and pressure filter:

  • The flow of water is not under gravity. This implies that water inside the closed chamber is under pressure.
  • The diameter of the tank is 1.5 m - 3 m and the height or length is 3.5 to 8 m.
  • Operation is the same as rapid gravity filter.
  • Rate of filtration is 6000 - 15000 l/m2/hr.

Related Questions

Consider the following statements in respect of slow sand filter and rapid sand filter: 1. The two filters differ in respect of the standards regarding the non-uniformity of the sand used in their filtering media. 2. The two filters do not differ in respect of the effective size of the sand used in them. 3. The two filters differ in respect of their respective under-drainage system. 4. The two filters differ in respect of their respective rate of filtration. Which of the above statements are correct? 
Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters.
Reason R: The sand used in slow sand filters is finer than that in rapid sand filters
Select your answer based on the coding system given below:
Cleaning is done by
(i) Scraping and removal in filters slow sand
(ii) Back washing in slow sand filters
(iii) Scraping and removal in filters rapid sand
(iv) Back washing in rapid sand filters
The correct answer is
Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters.Reason R: The sand used in slow sand filters is finer than that in rapid sand filtersSelect your answer based on the coding system given below:
Cleaning is done by (i) Scraping and removal in filters slow sand (ii) Back washing in slow sand filters (iii) Scraping and removal in filters rapid sand (iv) Back washing in rapid sand filtersThe correct answer is
Consider the following statement. i. The penetration of suspended matter is deep in the slow sand filter ii. The penetration of suspended matter is superficial in the rapid sand filter iii. Coagulation is not required in the slow sand filter Which of the above statement is/are correct?
Consider the following statement. i. Slow sand filter is not flexible in variation in demand ii. The rapid sand filter is flexible in fluctuations in demand iii. The method of cleaning of a slow sand filter involves agitation and back-washing Which of the above statement is/are correct?
Consider the following statement. i. The slow sand filter is not efficient in removing turbidity ii. The slow sand filter has a high initial cost iii. Skilled supervision is required in slow sand filter Which of the above statement is/are correct?
The following are certain operating problems of a rapid sand filter: 1. Sand depth should never be depleted by more than 10 cm. 2. Air binding results due to development of negative head and formation of air bubbles in the filter sand. 3. Water softening with lime-soda leads to incrustation of sand. 4. Bumping of filter bed is caused due to negative head. Which of the above statements are correct?
In the following passage some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of thefour alternatives. _____________ nearly eight decades, the women's movement __________ and debated the desirability and feasibility of a Uniform Civil Code,and has ended up ___________ a simple question — what is the value of uniformity? Is it for the "integrity of the nation" that uniformity in lawsis required, as some judicial pronouncements ___________? If so, who exactly is the beneficiary? Which sections of people benefit from"integrity of the nation", that abstract entity which is not exactly _______ the top of your mind as your husband throws you out on the street? and has ended up ___________ a simple question — what is the value of uniformity?