In the SV-30 test, sludge level and condition should be assessed at least every how many minutes?

• A. 1
• B. 3
• C. 5
• D. 10

Answer: (C)

Watching how the sludge settles over the full 30 minutes is key to judging its performance. Taking measurements of both sludge level and its condition at five-minute intervals gives you a balanced, practical set of data points (at 0, 5, 10, 15, 20, 25, and 30 minutes) that clearly show how quickly solids settle and whether the sludge remains well-flocculated or starts to form scum or float. This cadence captures the early settling dynamics and the overall trend without drowning you in measurements.

Choosing a different interval would either miss important changes or create unnecessary data. Checking every minute would be excessive, while a three-minute or ten-minute interval would either clutter interpretation or skip early settling changes that are important for assessing sludge quality. Five minutes hits the sweet spot for reliable interpretation within the SV-30 test.