Water Treatment "Part 16": Slow Sand Filtration.

avatar

One of the earliest techniques for treating water is slow filtration over a layer of fine sand, with particle diameters between 0.2 and 0.6 mm. This technique is a replacement to the use of chemicals when the objective is to remove microorganisms. This approach was utilised in the nineteenth century and is still used today in many purification facilities for weakly contaminated water. In the last step of treatment, slow sand filters are often used, due to the fact that the water at this stage seldom includes impurities, this extends filters lives for a number of years.


Slow sand filter profile

To get the necessary flows, this approach requires large basins. Water moves through filters with one-meter-thick sand layers at a relatively modest rate of 3.5 to 7.5 cubic metres of water per square metre of filter surface in a 24-hour period.

Due to the build-up of a layer of microorganisms on its surface, which serve as a coagulant for colloids, slow filtration offers ideal conditions for the biological treatment of water. The organic substances present in raw water also begin to break down at the same time. In addition, more than 95% of intestinal bacteria are captured by the filter surface. These bacteria can cause a decrease in the flow through the filter if its quantity exceeds a certain limit. In this case, a part of the sand layer must be removed and replaced with new sand.

References:

hive-196387 science ocd palnet stemgeeks proofofbrain ecency water chemistry neoxian
0
0
0.000
0 comments