Sewage disposal practice in large cities — which method is commonly adopted (historical MCQ perspective)?

Introduction / Context:
Historically, large coastal or riverine cities often relied on the “dilution” principle—discharging treated or partially treated effluent into a large body of water with sufficient assimilative capacity. Modern practice emphasizes advanced treatment to meet discharge standards; however, this classic MCQ reflects the traditional approach where extensive land for irrigation or oxidation ponds was unavailable in dense urban areas.

Given Data / Assumptions:

• “Large cities” with limited land resources.
• Access to large receiving waters (sea/major river) to dilute after treatment.
• Question framed in the context of conventional multiple-choice knowledge.

Concept / Approach:

Where vast land areas for sewage farming (irrigation) or stabilization ponds (oxidation) are impractical, outfalls to large water bodies have been commonly used, contingent on primary/secondary treatment and dilution to meet water quality criteria. Putrefaction is not a disposal method; it is an undesirable anaerobic decomposition process.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Many legacy metropolitan systems historically discharged to coastal waters post-treatment; modern upgrades add tertiary treatment and outfall diffusers.

Why Other Options Are Wrong:

Irrigation/oxidation need large land tracts; putrefaction is not a planned disposal method.

Common Pitfalls (misconceptions, mistakes):

Assuming “dilution is the solution to pollution” without acknowledging current environmental regulations; confusing process steps with disposal methods.

Final Answer:

dilution