If I were to write a short feature based on this as a mystery or lost document:
It appears the keyword may be a typo or a scrambled combination of terms. The most likely intended searches are: atv dvwk a 131 epdf top
Beuth (now part of VDE Verlag) is the official distributor for German technical rules. They offer the ATV-DVWK-A 131E PDF with a digital watermark (your name/company). While not free, it is legally secure and internationally recognized. If I were to write a short feature
Methods for calculating biological reactor and secondary settling tank dimensions. Nutrient Control: oxygen transfer needs
Engineers often use specialized software to apply these complex calculations:
This includes calculating the required sludge age , oxygen transfer needs, and the necessary volume for nitrification and denitrification.