Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

Proper backwashing of a sand filter requires the filter media to expand by what percentage?

1. 10-20%

2. 20-30%

3. 30-50%

4. 50-60%

The correct answer is: 30-50%

Proper backwashing of a sand filter is essential for maintaining its efficiency and effectiveness in treating water. During the backwashing process, water is passed through the filter in the reverse direction to remove accumulated debris, particles, and contaminants from the filter media. The correct expansion percentage of 30-50% during backwashing is critical because it allows for sufficient agitation of the sand particles. This expansion creates gaps between the grains, which helps dislodge trapped materials. If the media does not expand enough, these particles can remain lodged in the filter, reducing its performance and increasing pressure alongside the possibility of breakthrough, where untreated water passes through the filter. Backwashing at the appropriate expansion percentage not only enhances the cleaning process but also helps maintain the structural integrity of the filter media, ensuring a longer lifespan and more consistent water quality output. An expansion that is too low may not effectively clean the filter, while an expansion that is too high can lead to problems with media loss and stability. This is why ensuring a proper expansion of 30-50% during backwashing is optimal for sand filters.