Settled activated sludge is generally how compared to raw sludge?

Settled activated sludge is generally thinner when compared to raw sludge due to the removal of a significant portion of water content and solids during the settling process. In activated sludge systems, the aeration and biological treatment encourage the growth of microorganisms that consume organic matter. After aeration, the mixture is allowed to settle, and the heavier biomass (or sludge) settles at the bottom, while the lighter treated effluent is removed from the top.

This settling action concentrates the solids that remain, which results in a reduced volume of sludge containing a higher concentration of activated microorganisms relative to the influent or raw sludge. Consequently, the density of settled activated sludge is lower, leading it to be categorized as "thinner" compared to the original raw sludge. Understanding this differentiation is crucial for proper management of wastewater treatment processes.