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Pump little filthy (gray) water up from a container to filter down a growth bed for plants. A cloth strip runs in a closed loop, soaking up water and filth. that is squeezed out at the top.

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Idea on paper Fivefold reduction of cost Applicable within poverty Health Comfort Urban

A gray dirty water filter like Green Walls needs a tiny but continuous feed of the waste water of one family. This quantity can be estimated as 200 liters per day (5 persons, using 40 liters each) and has to be brought up to the filter evenly spread over a day. Apart from the gray water, It should also bring up sludge that collects on the surface and on the bottom of the gray water tank.
This sludge pump should be affordable in urban slums. A small solar panel should be sufficient to drive it. It should be reliable and easy to maintain.

A narrow strip of cloth, its ends connected into a loop, can run around over a roller in the top of the loop. From there it hangs down, with its lower end hanging in the gray water tank, just touching its bottom. The cloth loop runs around when the top roller is driven by a small solar panel. Water with sludge is soaked up in the tank. This water is presses out at the top by a second roller, running with some pressure against the first roller. The roller that squizes out the water is placed in such a position to hte driving roller, that the water squized out can not run back along the strip of cloth. Instead it is guided to the filter bed.

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sludge pump, low lift pump, dirty water pump, ....