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Which is the first zone of purification in a sand bed?
EXPLANATION
Earth Spheres , Vertical Thermal Stratificati
- Schmutzdecke Layer in Sand Filtration:
- In slow sand filters, the primary purification mechanism occurs within the uppermost biological skin formed on the top 1–2 cm of the sand bed, known in sanitary engineering as the Schmutzdecke zone (German for "dirty layer").
- Consists of a gelatinous matrix of algae, bacteria, protozoa, and plankton that metabolizes organic matter, traps particulates, and adsorbs pathogens. (Correct answer: Option 2)
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