Sludge blanket response to storm surge in an activated-sludge clarifier

Aspects of operation and design for storm flows at a 190-m(3)/h (1.2-mgd) d ry weather design flow activated-sludge plant were tested. A significant pl ant enlargement allowed recycle of test clarifier effluent to the main plan t 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 lag ged approximately 1 hour behind the start of the storm flow. This required an adjustment of the power equation model used. Furthermore. when the overf low rate exceeded the settling velocity of the feed solids. the sludge blan ket rose faster than the model prediction. This phenomenon required develop ing a new model to predict blanket behavior under various loading condition s. The new model allows for plant design to more accurately include a clari fier zone for storing solids during peak flows associated with rain storms. 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 b lanket prediction. Results are compared with those of other research for so lids storage during peak flow.