Water quality and stream sanitation basics: Identify the correct statements about dilution, self-purification, photosynthesis, and grab sampling in wastewater studies.

Introduction / Context:
Sanitation engineering combines laboratory testing with stream processes and basic biology. Clear terminology ensures correct interpretation of field and lab results when assessing wastewater impacts and treatment performance.

Given Data / Assumptions:

• Dilution and receiving water behavior influence observed concentrations.
• Self-purification integrates biodegradation and re-aeration.
• Photosynthesis by algae/macrophytes requires light.
• Grab sampling aims for a representative snapshot with adequate mixing.

Concept / Approach:

Each statement reflects standard practice: dilution factor compares volumes; self-purification describes natural recovery; photosynthesis is light-dependent; and for quickly collected grab samples, locations with turbulence (surface/baffles/mixers) are often chosen to better represent the bulk flow at that instant (site-specific judgment still applies).

Step-by-Step Solution:

Verification / Alternative check:

Use composite sampling for time-averaged quality; apply DO sag modeling to validate self-purification behavior.

Why Other Options Are Wrong:

In this set, all individual statements are valid; therefore “All the above” is correct.

Common Pitfalls:

Confusing dilution with decay; sampling in unmixed zones; interpreting photosynthetic DO spikes as sustained recovery.

Final Answer:

All the above