Recognizing sewage quality: which statements about appearance and odour correctly characterize strong, fresh, and septic sewage?

Introduction / Context:
Visual and olfactory indicators provide quick field assessments of sewage condition when laboratory analysis is unavailable. These cues help operators identify onset of septic conditions, verify aeration performance, and anticipate odor complaints.

Given Data / Assumptions:

• Typical municipal sewage without unusual industrial discharges.
• Warm-weather conditions can accelerate septic onset.
• Normal conveyance times from sources to treatment.

Concept / Approach:

“Strong” sewage has higher suspended and dissolved organic load, giving greater turbidity. Fresh sewage (recently generated) is generally grayish and nearly odourless. Without aeration, biological oxygen demand rapidly depletes dissolved oxygen; anaerobic processes then produce black color (sulfides) and offensive odors (e.g., hydrogen sulfide), often within a few hours depending on temperature and retention time.

Step-by-Step Solution:

Verification / Alternative check:

Routine plant observations: increasing retention with poor ventilation correlates with blackening and odor complaints; laboratory measures (DO, ORP) corroborate field signs.

Why Other Options Are Wrong:

Each individual statement is correct; only “All the above” captures the full characterization.

Common Pitfalls:

Assuming clear sewage is low-strength; some dissolved organics do not add turbidity. Misattributing black colour to industrial dyes rather than sulfide formation without testing.

Final Answer:

All the above.