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.