Untreated sludge drawn from a primary sedimentation tank normally would contain 1000 to 3000 mg/L of settleable solids. True or False?

Untreated sludge drawn from a primary sedimentation tank normally would contain 1000 to 3000 mg/L of settleable solids. True or False?

• A. True
• B. False
• C. Not sure
• D. Depends on influent

Answer: (B)

When sludge is drawn from the primary sedimentation tank, it is already a highly concentrated stream. Primary sludge typically contains solids on the order of about 2–4% by weight, which corresponds to roughly 20,000–40,000 mg/L of solids. That means the settleable solids concentration in untreated primary sludge is far higher than 1000–3000 mg/L. So the statement is false. In other words, you’d expect a much thicker sludge with solids concentrations in the tens of thousands of mg/L, not just a few thousand.

When sludge is drawn from the primary sedimentation tank, it is already a highly concentrated stream. Primary sludge typically contains solids on the order of about 2–4% by weight, which corresponds to roughly 20,000–40,000 mg/L of solids. That means the settleable solids concentration in untreated primary sludge is far higher than 1000–3000 mg/L. So the statement is false. In other words, you’d expect a much thicker sludge with solids concentrations in the tens of thousands of mg/L, not just a few thousand.