Activated Sludge Process Control: Alabama Grade III
Grade III covers Alabama's mid-size mechanical plants: trickling filter/biological contactor plants from 1.000 to 15.000 MGD, or activated sludge plants from 1.000 to 5.000 MGD. At this scale, plants typically run continuous, instrumented process control rather than the simpler operation of a Grade II package plant, and permit limits often begin to include nutrients, not just BOD/TSS.
Process control math and monitoring
Grade III operators are expected to calculate and interpret: F:M ratio (food-to-microorganism ratio — organic loading per pound of mixed liquor volatile suspended solids, MLVSS), mean cell residence time / sludge age (how long biomass stays in the system, which governs nitrification capability and settleability), sludge volume index (SVI, from a 30-minute settling test, used to judge whether sludge will settle wel