Is there a mimimum diameter for slow sand filters?
Probably. If filter tanks are too small in diameter, the ratio of filter bed to side wall surface area reaches a point where slipstreaming may occur down the sidwall, avoiding the biolayer entirely. As a rule of thumb, Blue Future Filters are never less than 18″ diameter for safety. We know of “filters” that have been deployed without concern for diameter or flow rate that have resulted in cases of Cholera.
