"ATV-DVWK-A 131 E" is the English edition of a German technical rule known as the "Arbeitsblatt ATV-DVWK-A 131" (Guideline). The abbreviation "E" stands for the English edition, as the rule is also available in its original German. The full title of the document is: . It was created by the German Association for Water, Wastewater and Waste (then known as ATV-DVWK) and is a comprehensive design manual for engineers, plant operators, and scientists.
The standard covers the removal of carbon, nitrogen, and phosphorus. Atv Dvwk A 131 E.pdf