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Gota de Esperança - Areia e Cascalho

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Optional: Download English BioSand Filter PowerPoint - 'Find Sand and Gravel'

Stage B: Find Sand and Gravel

Selecting and preparing the filtration sand and gravel is very important for the treatment efficiency of the BioSand filter. While not complicated, the steps in preparing the filtration sand must be followed exactly as presented. Poor selection and preparation of the filtration sand could lead to poor performance and a lot more work to fix the problem.

What kind of sand do I need?

Where can I find sand?

#1 ROCK CRUSHER

Sand and gravel from a rock crushing machine is called crushed rock. Crushed rock has a good mixture of grain sizes, which is important for proper functioning of the filter. It is also less likely to be contaminated by pathogens or organic matter.

Crushed rock is the BEST sand and gravel to use for inside the filter. You can also use it for the concrete.

#2 SAND QUARRY

If crushed rock is absolutely not available, the next choice is sand from a sand quarry or pit. Sometimes you can get gravel there too. It is usually not as clean as crushed rock - it may be contaminated with pathogens or organic matter. Check to make sure the sand has a variety of grain sizes and that it is clean.

#3 . RIVER

The sand and gravel from a river are not clean. They have dirt, leaves and sticks, and pathogens in them. If you use river sand, it takes more work to make it clean. You can use river sand to make the concrete filter container. River sand is not good sand for inside the filter.

Crushed rock makes the best filtration sand. It may be hard to find and it may be more expensive than river sand. But you should use crushed rock! If crushed rock is very expensive, buy crushed rock to use only for the sand and gravel inside the filter. You can buy river sand and construction gravel to make the concrete filter container.

Things to Look for when Selecting Sand for Inside the Filter

When you pick up a handful of the sand, you should be able to feel the coarseness of the grains.

You should be able to clearly see the individual grains, and the grains should be of different sizes and shapes.
When you squeeze a handful of dry sand and then you open your hand, the sand should all pour smoothly out of your hand.
If you are buying mixed sand and gravel, it should have a lot of gravel pieces up to 12 mm (½") in diameter.
It should NOT contain any organic material (e.g. leaves, grass, sticks, loam, dirt).
It should NOT contain possible microbiological contamination.
It should NOT be from an area that has been used a lot by people or animals.
It should NOT be very fine sand nor sand that is mostly silt and clay.
When you squeeze a handful of dry sand, it should NOT ball up in your hand or stick to your hand. If it does, it probably contains a lot of dirt or clay.
It should NOT have much gravel larger than 12 mm (½"). Any gravel larger than 12 mm (½") is waste and will not be used inside the filter or in the concrete.

Dry the sand and gravel

When the sand and gravel is delivered, you need to dry it and store it until you are ready to sieve it.

If the sand is wet, dry it.
Spread the sand very thinly on a platform or table that is up above the ground. Turn it with a shovel sometimes so it all gets very dry.

Be careful the sand does not get dirty. Dirt and leaves can blow into the sand while it is drying.
Store the dry sand where it will stay dry and clean.