Unit 1

• Flushing Tank in Sewerage Systems:
• specialized masonry chamber equipped with an automatic siphonic discharge mechanism built at the head of flat-gradient sewer branches.
• Periodically discharges a large volume of water at high velocity to scour and flush out settled sludge, grit, and solids, effectively preventing clogging in sewer pipes. (Correct answer: Option 3)

• Microbial Transformation: Biological soil remediation (bioremediation) functions primarily through the metabolic and enzymatic transformation of toxic organic contaminants into harmless end-products (such as $\text{CO}_2$, $\text{H}_2\text{O}$, and non-toxic biomass).
• Distinction from Physical Methods: Vitrification and soil washing are physical/thermal methods, whereas bioleaching specifically dissolves metal ores/sulfides through microbial acid generation.

Correct option: (2) Transformation