Waiting Period After Cleaning a Slow Sand Filter
(A) Up to 6 hours
(B) 6 hours to 12 hours
(C) 12 hours to 24 hours
(D) 24 hours to 48 hours
Explanation
A slow sand filter relies on a biological layer called the schmutzdecke, which forms on the surface of the sand bed and is critical for effective filtration. This layer consists of microorganisms that trap and break down impurities in the water. When a slow sand filter is cleaned, the schmutzdecke is disrupted or removed, and it requires time to reform and regain its filtration efficiency.
Water filtered immediately after cleaning may not meet required purity standards due to the absence of a fully functional schmutzdecke. Therefore, it is standard practice to discard or bypass the filtered water for 24 to 48 hours until the biological layer is re-established and effective filtration is restored.
Key Aspects of Slow Sand Filter Cleaning
| Aspect | Description |
|---|---|
| Schmutzdecke | Biological layer of microorganisms on the sand surface that traps and degrades impurities. |
| Cleaning Process | Involves scraping off the top layer of sand (including the schmutzdecke) to remove accumulated debris. |
| Reformation Time | Takes 24 to 48 hours for the schmutzdecke to reform and restore filtration efficiency. |
| Post-Cleaning Action | Filtered water is discarded or diverted until the biological layer is effective again. |
Key Notes
- The schmutzdecke is essential for the slow sand filter’s ability to remove pathogens and impurities.
- The 24-to-48-hour waiting period ensures that the filtered water meets safety and quality standards.
- Slow sand filters are widely used in water treatment for their simplicity and effectiveness in small-scale and rural settings.
- Regular maintenance and proper post-cleaning protocols are critical for the reliable operation of slow sand filters.
Note: Proper management of slow sand filters, including allowing sufficient time for the schmutzdecke to reform after cleaning, is essential for ensuring safe and clean drinking water in environmental engineering.
More solved questions of APSC WRD AE 2019, HERE
For APSC Water Resources Civil 2019 Question Paper, Click Here
For APSC Previous Year AE Question Paper, Click Here
For APSC Previous Year JE Question Paper, Click Here