A household in a peri-urban settlement installs a septic tank because sewerage is unavailable. The essential principle underlying the working of a septic tank is:

• A Aerobic oxidation of sewage by surface aeration over 6 hours
• B Trickling of sewage over stone media colonised by aerobic biofilm
• C Chemical precipitation of solids by added lime and alum
• D Anaerobic digestion of settled organic solids with a detention period of about 12 to 36 hours ✓

Explanation

A septic tank is a watertight chamber in which sewage is retained for roughly 12 to 36 hours, commonly cited as 24 hours. Solids settle, and the accumulated sludge undergoes anaerobic digestion, reducing its volume and releasing gases such as methane and hydrogen sulphide. The supernatant effluent passes to a soak pit for subsoil dispersion. Trickling filters and activated sludge are aerobic municipal processes, and no chemicals are added.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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