Wastewater quality basics: Select the correct statements about pH and the typical pH of fresh domestic sewage.

Introduction / Context:

pH is a fundamental parameter in wastewater engineering. It influences biological activity, corrosion/scale tendencies in sewers, and the effectiveness of many treatment processes such as coagulation and disinfection.

Given Data / Assumptions:

• The statements describe what pH represents and typical pH ranges in fresh sewage.
• Fresh domestic sewage commonly shows mild alkalinity (pH slightly above 7).
• Anaerobic decomposition over time may reduce pH (becoming acidic), but that is not “fresh.”

Concept / Approach:

By definition, pH < 7 is acidic, pH = 7 is neutral, and pH > 7 is alkaline. Fresh municipal sewage typically has a pH around 7.2–8.0 due to bicarbonate alkalinity and the nature of household waste streams.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals for wastewater treatment list typical fresh sewage pH as mildly alkaline; long retention (septic conditions) often shifts pH downward.

Why Other Options Are Wrong:

• Each individual statement (a–d) is correct; therefore “All the above” is the most complete choice.

Common Pitfalls:

• Assuming all sewage is acidic; freshness and aeration conditions matter.
• Ignoring industrial inputs which can alter pH significantly.

Final Answer:

All the above.