SLOW SAND FILTER



Slow sand filters are the least complex type of granular media filter. They are typically housed in reinforced concrete structures, with a basin with a bed of relatively fine sand placed over support gravel (0.3–0.6 m in depth) and under drain piping up to 0.9–1.5 m in length.

 A slow sand filter consists basically of three different layers within a filter box. These layers are from bottom to top: the under drainage system, the gravel layer and the sand.

It is only the sand which plays any part in the treatment process. The gravel layer Is arranged in four graded levels.

What is the biggest advantage of slow sand filtration?

A slow sand filtration system—properly designed, operated and maintained—will successfully remove disease-causing organisms like Giardia, Cryptosporidium, bacteria, and viruses.

Where is slow sand filter suitable?

Slow sand filters are typically used to treat surface water sources, such as lakes, rivers, and streams. They are not recommended for use with groundwater sources, as they may not remove certain contaminants.

What are the 2 types of sand filters?

Rapid (gravity) sand filters

Rapid (pressure) sand bed filters.

What is the slow sand method?

Slow sand filtration is a simple and reliable process. They are relatively inexpensive to build, but do require highly skilled operators. The process percolates untreated water slowly through a bed of porous sand, with the influent water introduced over the surface of the filter, and then drained from the bottom.

The slow sand filter has many advantages and disadvantages, including:

·         Simplicity of its design and operation.

·         Low maintenance cost.

·         Low overall cost.

·         Its ability to remove small-sized dirt (20-40 microns) and debris.

·         Requires no pre-treatment or extensive factory control.

·         It does not require a lot of energy to run

What is the efficiency of sand filter?

Depending on the sand effective size, the sand filter achieved turbidity reductions of between 59.6 and 85.4% and dissolved oxygen recoveries from 4.5 to 15.7%. During the experiment the filter ripening period was 15 min.

 How thick is a slow sand filter?

Detailed Solution

Item

Slow Sand Filter

Filter sand Effective size Uniformity coefficient The thickness of sand bed

0.2 to 0.4 mm 1.8 - 3 90 to 110 cm

Under drainage system

Open jointed pipes or drains covered with perforated blocks

Size of each unit

50 to 200 sq.m

Rate of filtration

100 to 200 Lph/sq.m

 


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