The liquid stream isn't the whole plant — everything the primary clarifier and the WAS pumps remove has to go somewhere, and a Class A operator needs to size the digester that receives it, verify its performance, and account for what leaves as finished biosolids, which is exactly what this guide's design math and mock exam set cover.
Digester Sizing: From Feed Rate to Required Volume
Where the System Optimization guide calculated the detention time of an existing digester, sizing math runs the same relationship in reverse: given a design feed rate and a target detention time, determine the digester volume needed.
Required Volume (gal)=Feed Rate (gpd)×Design Detention Time (days) Worked Example 1
A plant's combined primary and waste-activated sludge feed to digestion totals 42,000 gpd. The design target is a 18-day detention time (a commonly