In the video it is correct that water and air help clean the sand, but there is a multiple step process. First it is air by itself, then air and a little water flow, and then air is usually shut off when there is more water flow. If air and a big flow were used in the backwash then too much of the sand would be taken with it and thrown away. It's better that the sand be kept and used over and over.
Ilham Andreansyah - FTI UJ Thank you very much for the explanation, on this occasion I learned a lot in this video about step by step the backwash process for water filters. Backwash is important for maintaning the quality of process.
Usually it's a sand put through screens to make a certain grain size. But sometimes granulated carbon is used instead of sand, or maybe a combination. The backwash makes the heavier material (sand) go to the bottom layer and the carbon would be the upper layers.
Thousands, maybe 10 thousand for that one filter, but usually the one shown in the video is one of a string of filters, maybe 5 or six. The filtered water can also be estimated by the surface area. But the backwash uses about 5 - 10% of the water filtered. We can't tell from the video.
Too many sand and effort if we use for small quantity water cleaning, if asked to choose, i prefer make many layer of sand and rock and then run dirtywater pass into sand and rock
This is a "rapid sand filter" that uses chemicals to group together the dirt in the water, then it clings to the sand until the cleaning you saw in the video. It has lots of pumps, chemicals, energy, valves, and needs to be operated by trained technicians. There's another kind called "slow sand filtration" that is much slower to filter, takes more space, but does not required chemicals and is easy to use. This kind can be used in a house or for a village or even a city if there is space for it. Slow sand filtration uses a biological film over the sand that does the work. It was used in Europe in the late 1800's and then world wide, and is still in use, but for large cities it takes too much space and is too slow.
