In the activated sludge process, settling performance is the final barrier determining effluent quality. SVI (Sludge Volume Index) is the most classic and widely used indicator for evaluating the settling performance of activated sludge—it helps us determine whether the sludge is "settling healthily" or "bulking." A simple number contains rich information about the sludge's condition. In daily operations, personnel often use SV30 (Sludge Volume Index after 30 minutes) to observe sludge settling. However, SV30 is greatly affected by the sludge concentration (MLSS). The same settling volume means completely different things at different MLSS levels. SVI cleverly combines the two, eliminating the influence of concentration differences, and thus can more accurately evaluate the flocculation and sedimentation performance of activated sludge than SV values alone.
