schmutzdecke
n.— «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.» —by Amory Prescott Folwell Water-supply Engineering: The Designing and Constructing of Water-supply Systems (New York) , 1917. (source: Double-Tongued Dictionary)
Further reading
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