Vital layer in slow - sand filter is of? - Raj. CHO -2024

Raj. CHO -2024

Community Health Nursing

Easy

Appeared in: Raj. CHO -2024

Explanation

Schmutzdecke, which is the German term for 'dirt cover'.
This layer is also known as the vital layer, zoogleal layer, or biological layer.
It is a slimy, gelatinous film that forms on the surface of the sand in a slow sand filter.
The Schmutzdecke is a living layer composed of algae, plankton, diatoms, and bacteria that are responsible for the biological purification of water.
It effectively removes organic matter, traps bacteria, and oxidizes ammonia, making the water safe to drink.

Option A: The under drainage system is a structural component located at the bottom of the filter. Its function is to collect the filtered water and support the sand bed, not to perform biological filtration.
Option B: Alum is a chemical coagulant used to form a floc (Alum-Hoc) in rapid sand filters to trap impurities. Slow sand filters do not use chemical coagulants; they rely on a biological process.
Option C: The sand bed is the main body of the filter and provides the physical medium for filtration and a surface for the vital layer to grow. However, the sand itself is primarily a mechanical strainer; the 'vital' biological action occurs in the Schmutzdecke layer on top of it.

Visual 1: Diagram of a Slow Sand Filter. A cross-section diagram showing the different layers: supernatant water, Schmutzdecke (vital layer), sand bed, gravel support, and the under-drainage system. This helps visualize the position and relationship of each component.
Visual 2: Flowchart comparing Slow and Rapid Sand Filtration. A chart outlining the steps for each process, highlighting key differences like the use of coagulants, filtration rate, and cleaning methods.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Water purification methods, specifically the components and mechanism of a slow sand filter as background academic context rather than a clinical decision trigger.
Understanding water purification methods like slow sand filtration is fundamental in community health nursing for preventing waterborne diseases (e.g., cholera, typhoid, hepatitis A).
Nurses play a crucial role in health education, teaching communities about the importance of safe drinking water and simple purification methods, especially in rural or resource-limited settings.
What if? If a community's water source is highly turbid (cloudy), a slow sand filter might become clogged quickly. In this case, pre-treatment like simple sedimentation or storage would be necessary before filtration, and a nurse would advise the community accordingly to maintain the water supply.

How to Approach the Question

First, identify the key terms in the question: 'Vital layer' and 'slow-sand filter'.
This is a factual recall question that tests knowledge of water purification terminology.
Recall the specific components of a slow sand filter and their functions.
The term 'vital layer' implies a living, biological component essential for the purification process.
Evaluate the options: 'Under drainage' and 'Sand bed' are structural parts. 'Alum-Hoc' is associated with rapid, not slow, sand filters.
This leaves 'Schmutzdecke', the specific term for the biological layer, as the correct answer.

Concept Tested & Keywords

Concept Tested: Water purification methods, specifically the components and mechanism of a slow sand filter.
Stem keywords: Vital layer, slow-sand filter
Lead-in keywords: is of
Negative lead-in flag: false

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