schmutzdecke
n.— «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.» —“Tender—Department Of The Environment For Northern Ireland Water Executive—Central Design Unit” Contract Journal January 27, 1994. (source: Double-Tongued Dictionary)
Further reading
Enthusiastic book recommendations! Martha’s savoring the biography of Alexander von Humboldt, the 19th-century explorer, polymath, and naturalist who revolutionized our understanding of nature and predicted the effects of human activity on...
The words tough, through, and dough all end in O-U-G-H. So why don’t they rhyme? A lively new book addresses the many quirks of English by explaining the history of words and phrases. And: have you ever been in a situation where a group makes...