Question

The cleaning of slow sand filter is done by

• A. reversing the direction of flow of water
• B. Scraping off top layers of sand and admitting water
• C. Passing air through the filter
• D. Passing a solution of alum and lime through the filter

Answer 1

The correct option is B Scraping off top layers of sand and admitting water

(d) The cleaning of slow sand filters is not done by backwashing as is done for rapid gravity filters, but is done by scrapping and removing the 1.5 to 3 cm of top sand layer. The top surface is finally racked, roughened, cleaned and washed with good water.