Which procedure is used to determine MLSS in a sludge sample?

• A. Remix
• B. Filter
• C. Allow to stand
• D. Acidity

Answer: (B)

MLSS is found by physically separating the suspended solids from the liquid and then measuring how much solid mass is present in a known volume. The way this is done is to filter a measured amount of mixed liquor so the solids are captured on a filter, dry the filter with the captured solids to constant weight, and weigh it. The mass of dried solids (after subtracting the empty filter’s weight) divided by the volume filtered gives the MLSS in mg per liter. This filtration step is essential because it isolates the solids from the liquid; simply remixing won’t separate them, letting the mixture stand won’t consistently remove all suspended solids, and acidity has no direct role in quantifying solids.