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Factors Affecting Sand Filter Operation and Handling Anomalies

  1. Filtration Rate: The filtration rate of a sand filter should not be excessively slow. A slow filtration rate reduces the water treatment per unit filter area. To achieve a specific water output, the filtration area must be increased, leading to higher investment. Conversely, if the filtration rate is too fast, it increases head loss, shortens the filtration cycle, and compromises the quality and quantity of the treated water. A general filtration rate is around 10-12m/h.

Shallow Sand Filter
  1. Backwashing: Backwashing is essential for removing mud and restoring the filtering capability of the filter bed. To clean the mud thoroughly, a specific backwashing speed and duration are required, depending on factors such as the size and relative density of the filter material, expansion rate, and water temperature. The backwashing intensity for quartz sand is typically 15L/(2.s). During backwashing, the bed expands by 25%-50%, and the backwashing time is 5-6 minutes. Effective backwashing ensures optimal sand filter operation.

  2. Uniform Flow: Whether during operation or backwashing, it is crucial to have a uniform flow distribution across all sections. This is primarily dependent on a well-designed drainage system. Uniform flow is essential for achieving effective filtration.

  3. Backwashing Period: To maintain filtration effectiveness, backwashing is typically performed every 2-3 days.

Anomalies and Remedial Measures in Sand Filter Operation:

Common Anomalies:

  1. Periodic reduction in water quantity during the filtration cycle.

Possible Causes:

  1. Clumping of filter sand with suspended solids.
  2. Insufficient backwashing intensity or incomplete backwashing.
  3. Extended backwashing cycle.
  4. Malfunction in the distribution or drainage system causing uneven flow.
  5. Filter bed height too low, resulting in sudden turbidity in the raw water.
  6. Sudden turbidity in the raw water.

Remedial Measures:

  1. Intensify backwashing and clarify water quality.
  2. Adjust water pressure and flow rate.
  3. Increase backwashing frequency and shorten the backwashing cycle as needed.
  4. Inspect the distribution or drainage system.
  5. Adjust the filter bed height appropriately.
  6. Strengthen the analysis and clarification of raw water quality.

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