Which type of sludge is typically expected to have a higher settleability and lower volume in a thickening process?

Digested sludge is known for its improved settleability and reduced volume due to the breakdown of organic matter through anaerobic or aerobic digestion processes. During digestion, microorganisms decompose the organic materials in the sludge, leading to a decrease in the overall volume. This process not only stabilizes the sludge but also enhances its physical properties, resulting in a denser and more compact mass that settles more effectively when subjected to thickening.

The enhanced settleability of digested sludge is advantageous in wastewater treatment, allowing for more efficient separation of solids from liquids, which is critical in subsequent processes like dewatering or further treatment phases. In contrast, other sludge types, such as primary sludge, secondary sludge, and wasted activated sludge, generally contain higher amounts of volatile solids and require additional treatment steps for optimal settleability. Therefore, digested sludge stands out as the ideal choice in this context.