Why do solids-contact basins have much shorter detention times than conventional treatment basins?

Solids-contact basins are designed to optimize the interaction between solids and liquids, facilitating more efficient settling and treatment processes. The key to shorter detention times in solids-contact basins lies in the presence of the recycled materials from the sludge blanket. In this setup, a portion of the settled sludge is recycled back into the basin, enhancing the concentration of solids. This creates a more effective environment for coagulation and flocculation to occur, leading to faster sedimentation and reduced detention time.

The interaction between the recycled sludge and incoming wastewater increases the rate at which contaminants can be removed, allowing for quicker processing. By maintaining a thickened sludge blanket in the basin, these systems can achieve effective treatment within a shorter retention time compared to conventional basins, which rely solely on gravity for settling and therefore require longer times for effective treatment. This characteristic makes solids-contact basins particularly beneficial for operations where space or time constraints are a concern.