use of the diluted sludge volume index (OS VI) in mUg, based on a diluted 30-minute settling test (DSV30) in percent (mUdL), in which the sample is diluted to give a settled volume of less than 30%. The settling velocity of an undiluted sample was correlated with the diluted 30-minute settled sludge volume in an unstirred I-L graduated cylinder. For return sludge, the OSV30 was determined as DSVI X C, where C is the solids concentration in percent.At the time of the report by Garrett et al. (1984), principal models used to relate the settling velocity to solids concentration were the power model used by Yoshioka et al. ( 1957) and Dick and Young (1972) and the exponential model used by Vesilind (1968). These models, respectively, are as follows:ABSTRACT: Aspects of operation and design for stonn flows at a 190-m 3 /h (1.2-mgd) dry weather design flow activated-sludge plant were tested. A significant plant enlargement allowed recycle of test clarifier effluent to the main plant versus discharge to a stream. Thus it was possible to test high overflow rates without risk of a permit violation.On-line monitoring showed that the return sludge concentration increase lagged approximately I hour behind the start of the storm flow. This required an adjustment of the power equation model used. Furthermore, when the overflow rate exceeded the settling velocity of the feed solids, the sludge blanket rose faster than the model prediction. This phenomenon required developing a new model to predict blanket behavior under various loading conditions. The new model allows for plant design to more accurately include a clarifier zone for storing solids during peak flows associated with rain stornlS. An exponential equation, fitted to settling data, was also used in the new model with test data for comparison. The exponential equation gave a low blanket prediction. Results are compared with those of other research for solids storage during peak flow. Waler Environ. Res., 71,432 (1999).KEYWORDS: activated-sludge clarifier, diluted sludge volume index, floc volume flux, sedimentation model, sludge blanket model, storm flow. and Where Vs Vs = a X Xi-" at X e-n'XXi (I) (2)
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