Wisconsin DNR Wastewater Operator Certification Practice Test

Dewatered sludge is the solid mass left after removing as much water as practical from the sludge, so it becomes much more handleable. The typical solids content for this dewatered product is about 15 to 30 percent, which is enough to give it a compact, cake-like consistency rather than a loose slurry. That solid, cake-like form is why it’s commonly called cake sludge.

Ranges that are too low (5–10% solids) describe sludge that’s not truly dewatered and would still be quite watery. Ranges that are much higher (40–60% solids) describe material that's drier than usual for standard dewatering processes. The 25–35% range is close but not the standard reference value expected in many operations and exams, so the best match is the 15–30% range with the cake sludge nickname.