With reference to the composition of sewage, consider the following statements: 1. It is a liquid waste consisting entirely of dissolved impurities. 2. It contains nutrients such as phosphorus and nitrogen. 3. It is devoid of any saprophytic or disease-causing bacteria. Which of the statements given above is/are correct?

Correct Option The correct option is (b). Explanation Sewage is wastewater released by homes, industries, hospitals, offices, and other users. It is a complex liquid mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes, and disease-causing microbes. Statement-wise Analysis - Statement 1 is Incorrect. Sewage is not composed entirely of dissolved impurities. It is a complex mixture containing suspended solids (e.g., sand, silt, clay), colloidal material (e.g., fecal matter, bacteria, cloth, paper fibers), and dissolved materials (e.g., nutrients like nitrates, ammonia, phosphates, sodium, calcium). - Statement 2 is Correct. Sewage contains significant amounts of nutrients, specifically nitrogen and phosphorus. These originate from organic waste (human faeces, animal waste, urea) and inorganic sources (detergents, fertilizers). - Statement 3 is Incorrect. Sewage is rich in microorganisms. It contains saprophytic bacteria (decomposers) as well as disease-causing bacteria (pathogens) and other microbes responsible for water-borne diseases such as cholera, typhoid, and dysentery. Key Takeaway Sewage is a heterogeneous mixture comprising suspended solids, colloidal matter, and dissolved impurities (including nutrients like nitrogen and phosphorus), along with a high load of pathogenic and saprophytic microorganisms.

With reference to the composition of sewage,… - NCERT Class 7 Environment & Ecology MCQ

NCERT Class 7 Environment & Ecology — Chapter 2: Wastewater story

mcqmedium

With reference to the composition of sewage, consider the following statements:

It is a liquid waste consisting entirely of dissolved impurities.
It contains nutrients such as phosphorus and nitrogen.
It is devoid of any saprophytic or disease-causing bacteria.

Which of the statements given above is/are correct?

NCERT textbook question

From NCERT Science - class 7 · Page 157

Options

A1 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

Correct Option

The correct option is (b).

Explanation

Sewage is wastewater released by homes, industries, hospitals, offices, and other users. It is a complex liquid mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes, and disease-causing microbes.

Statement-wise Analysis

Statement 1 is Incorrect. Sewage is not composed entirely of dissolved impurities. It is a complex mixture containing suspended solids (e.g., sand, silt, clay), colloidal material (e.g., fecal matter, bacteria, cloth, paper fibers), and dissolved materials (e.g., nutrients like nitrates, ammonia, phosphates, sodium, calcium).
Statement 2 is Correct. Sewage contains significant amounts of nutrients, specifically nitrogen and phosphorus. These originate from organic waste (human faeces, animal waste, urea) and inorganic sources (detergents, fertilizers).
Statement 3 is Incorrect. Sewage is rich in microorganisms. It contains saprophytic bacteria (decomposers) as well as disease-causing bacteria (pathogens) and other microbes responsible for water-borne diseases such as cholera, typhoid, and dysentery.

Key Takeaway

Sewage is a heterogeneous mixture comprising suspended solids, colloidal matter, and dissolved impurities (including nutrients like nitrogen and phosphorus), along with a high load of pathogenic and saprophytic microorganisms.

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