schmutzdecke

n. a naturally occurring gelatinous layer of living biological matter on a sand-based water filter, for which it provides additional filtration. Subjects: German, Environment

Editorial Note: Occasionally spelled in English as “schmutzedecke” or “smutzdecke.” Etymological Note: German schmutz ‘dirt’ + decke ‘covering.’

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Citations: 1894 Report of the Secretary of War (Washington, D.C.) vol. II, part 6, p. 3249: After the filter has been operated for some time a gelatinous layer (Schmutzdecke of Piefke) is formed of such imperviousness that each square meter of surface will no longer furnish as much as 3 cubic meters (800 gallons) of water in twenty-four hours.…Whenever the demand for the filter is not too great it is allowed to rest after cleaning for some time, in the belief that those particles of the dirt deposit (Schmutzdecke) which have penetrated unto the lower layers will be oxidized under prolonged contact with the air. 1917 Amory Prescott Folwell Water-supply Engineering: The Designing and Constructing of Water-supply Systems (New York) p. 82: Most of this gelatinous growth and of the deposited sediment collects in the top half-inch or so of the bed, and combined form what the Germans call schmutzdecke, which term has been adopted in this country. This schmutzdecke acts as a finer straining medium for removing bacteria and other suspended matters. 1994 Contract Journal (January 27) “Tender—Department Of The Environment For Northern Ireland Water Executive—Central Design Unit” p. 35: Periodically the top layer of sand (approximately 25 to 100m deep) needs to be removed from the slow sand filters together with the associated biological accumulation ("schmutzdecke") for cleaning. 1994 Public Works (Apr. 15) “Filtration” vol. 125, no. 5, p. C19: This system, introduced into the U.S. in 1872, uses low water flow rates (0.05 gpm/sq ft) and relies on the formation of a “schmutzdecke” (a fine, mud-like layer) in the top surface of the fine sand (specific gravity of 2.6|+ or -~) for filtering. However, it may take several weeks for the filtration layer to form (during which the “filtered” water is lost) and this type filter is ineffective for high turbidity waters. Cleaning is by scraping off the schmutzdecke and top layer of sand, and placing a layer of new sand. 1996 [Bruce] Usenet: alt.tasteless (June 11) “You can bed on it!”: The surface is now a veritable <schmutzdecke> of cat hairs, dead fleas, some dirt I suppose, hair-balls and horked-up Friskies. 2007 James M. Dakin Bison Survival Blog (Jan. 20) “Sand Filter”: This type of filter works because of a biological microbe named schmutzdecke. It grows on top of the sand and its job is to eat organisms in the water. It can take up to two weeks to form so any water before that is not fit to drink. Also, to keep ol’ Schmutzy alive you need to keep the water level above the sand at all times.

Posted 16 Mar 07 | Permalink | Tell a Friend