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(Environmental Science) a layer of sand or gravel used to expose sewage effluent, in its final stages, to air and the action of microorganisms. Compare filter bed1
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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|Noun||1.||bacteria bed - layer of sand or gravel used to expose sewage effluent to air and the action of microorganisms|
filter - device that removes something from whatever passes through it
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