Domestic sewage composition (typical values): Approximately what fraction of most domestic sewage is solids by weight, with the remainder being water?

Introduction / Context:
Design and operation of sewers and treatment plants rely on typical ranges for wastewater composition. A key rule of thumb is that domestic sewage is mostly water with a tiny fraction of solids, which has profound implications for hydraulics, pumping energy, and treatment unit sizing.

Given Data / Assumptions:

• “Most domestic sewage” refers to combined domestic wastewater excluding unusual industrial inputs.
• Values are approximate and used for preliminary design and education.
• Solids include dissolve and suspended portions.

Concept / Approach:
Domestic sewage commonly contains about 0.1 percent solids (1,000 mg/L) and 99.9 percent water by weight. Understanding this helps students appreciate why processes like primary settling and biological treatment handle dilute streams yet must remove contaminants efficiently to protect receiving waters.

Step-by-Step Solution:
Recall the design heuristic: 99.9% water, ~0.1% solids.Eliminate unrealistic values: 5% or 10% solids would be sludge-like, not typical sewage.Select 0.1 percent as the best estimate.

Verification / Alternative check:
Measured total solids in municipal wastewater typically range near 700–1200 mg/L, aligning with ~0.1 percent by weight for domestic streams.

Why Other Options Are Wrong:
0.001 percent: too low for typical municipal influent.5 or 10 percent: orders of magnitude higher than observed; comparable to concentrated sludge.1 percent: higher than usual for raw sewage; could reflect thickened slurries.

Common Pitfalls:
Confusing total solids in raw sewage with sludge concentrations or industrial wastewater strengths.

Final Answer:
0.1 percent