In domestic water sewage, which of the following things is not a part of 'Dissolved materials'?

RRB Nsg. Superintendent 21 July 2019 (shift 1st)

Community Health Nursing

Easy

Appeared in: RRB Nsg. Superintendent 21 July 2019 (shift 1st)

Explanation

Sand is classified as a suspended solid, not a dissolved material, in the context of wastewater.
Suspended solids are insoluble inorganic or organic particles that are held in the water but will settle out when the water is still.
In the primary stage of sewage treatment, grit chambers are used to slow down the flow, allowing heavy particles like sand and gravel to settle and be removed.
Unlike dissolved materials, sand does not form a solution with water.

Option A: Nitrate (NO₃⁻) is a common dissolved nutrient found in sewage, often originating from the breakdown of organic waste.
Option B: Phosphate (PO₄³⁻) is another key dissolved nutrient in sewage, commonly from detergents and human waste.
Option C: Calcium (Ca²⁺) is a dissolved mineral ion commonly found in water, including sewage, and contributes to water hardness.

Visual 1: Diagram: A flowchart illustrating the composition of domestic sewage, breaking it down into water (99.9%) and impurities (0.1%), and then further categorizing the impurities into suspended solids (like sand), colloidal materials, and dissolved materials (like nitrates, phosphates, calcium).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of impurities in domestic sewage as background academic context rather than a clinical decision trigger.
Understanding the composition of sewage is fundamental in community health nursing for planning and implementing effective sanitation and waste disposal systems.
Proper sewage treatment, which involves removing different types of impurities in stages, is critical for preventing the spread of waterborne diseases like cholera, typhoid, and gastroenteritis.
What if? If a community's water source is contaminated with untreated sewage high in nitrates, it can lead to methemoglobinemia ('blue baby syndrome') in infants, a serious public health concern that a community health nurse should be aware of.

How to Approach the Question

First, identify the core concept being tested, which is the classification of impurities found in domestic sewage.
Note the negative keyword 'not'. The question asks you to find the option that does NOT fit the category of 'Dissolved materials'.
Recall or deduce the physical properties of each substance when mixed with water. 'Dissolved' means the substance breaks down into ions or molecules and mixes completely, becoming invisible.
Evaluate each option: Nitrate, phosphate, and calcium are chemical salts/ions that are known to be soluble in water.
Consider sand. Sand is made of small rock and mineral particles (like silica) that are insoluble in water. They may be suspended temporarily but will settle down.
Conclude that sand is a suspended solid, not a dissolved material, making it the correct answer.

Concept Tested & Keywords

Concept Tested: Classification of impurities in domestic sewage
Stem keywords: domestic water sewage, Dissolved materials
Lead-in keywords: not a part of
Negative lead-in flag: The question uses a negative framing ('not a part of'), asking to identify the substance that does not belong to the category of 'Dissolved materials'.

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