Most impoant layer of a slow sand filter is ?

Ans. is 'a' i.e., Vital layer o This is confusing one because of the following statements of Park. "The most impoant pa of the filter is the sand bed" - Park "The vital layer is the hea of the slow sand filter" - Park o Following statement may help in choosing the answer : ? "Vital layer is the layer that provides the effective purification in potable water treatment. the underlying sand layer providing the suppo medium for this biological treament layer" - Water & Healt 3rd/e 733. o Read the mechanism of action of slow sand filter and there will be no confusion. Mechanism of action of slow sand filter o Slow sand tiller work through the formation of a gelatinous layer called vital layer or hypogea I layer or Sch mu tzdecke in the top few cm of sand layer. o This layer is formed in the first 10-20 days of operation. o The formation of vital layer is known as "Ripening of the filter". o This vital layer consists of bacteria. fungi. Protozoa, and a range of aquatic insect larvae. o As waste passes through vital layer, paicles of foreign matter arc trapped in the mucilagenous matrix and dissolved organic material is absorbed and metabolized by bacterial, fungi and protoza --> Vital layer has mechanical (physical) as well as biological action. o So, the vital later acts as the hea of slow sand filter.