Which statement about septic tanks is incorrect? Evaluate the following statements about septic tanks and choose the incorrect one (if any).

Introduction / Context:
Septic tanks provide on-site primary treatment and anaerobic digestion for domestic wastewater in areas lacking centralized sewers. Understanding their essential features ensures proper design, siting, and operation, and helps distinguish them from other units like Imhoff tanks or aerated package plants.

Given Data / Assumptions:

• Domestic sewage strength within typical ranges.
• Single or two-compartment septic tank with baffles/tees to promote quiescence.
• Ventilation via vent pipes and access through manholes; tank covered for safety and odor control.

Concept / Approach:

Each statement is compared against standard septic tank characteristics. Septic tanks are indeed horizontal, continuous-flow settling tanks with anaerobic digestion. Detention periods commonly fall around 12–36 hours (varies with codes and loading). Tanks are covered and vented to manage gases like methane and hydrogen sulfide safely. Therefore, none of the statements is incorrect.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals for on-site wastewater systems reflect these features; installation standards require covers and venting; performance depends on sufficient detention.

Why Other Options Are Wrong:

Since (a)–(d) are correct, the only valid choice for an incorrect statement is (e) “None of these,” meaning none is incorrect.

Common Pitfalls:

Confusing septic tank detention with primary clarifiers in centralized plants; overlooking the need for regular sludge pumping; assuming aerobic processes dominate inside the tank.

Final Answer:

None of these