To neutralize acidic content that harms aquatic life.
Explanation
Industrial effluents, particularly from factories manufacturing batteries, chemicals, or textiles, often contain high concentrations of acids. Discharging highly acidic wastewater directly into natural water bodies alters the pH balance, creating a toxic environment for aquatic ecosystems.Detailed Analysis:
- To precipitate solid impurities. is incorrect: While certain bases can precipitate specific metal ions as hydroxides, the fundamental and primary objective of treating general acidic waste with bases is to adjust the pH, not merely to remove solids.
- To neutralize acidic content that harms aquatic life. is correct: The addition of basic substances (such as slaked lime or calcium hydroxide) to acidic waste initiates a neutralization reaction. This process raises the pH of the effluent to a neutral range (approximately pH 7) before discharge. Neutralizing the acid is critical because low pH levels can damage the gills of fish, inhibit the growth of aquatic plants, and disrupt the overall food chain.
- To increase the dissolved oxygen levels. is incorrect: Dissolved oxygen levels are typically managed through physical aeration processes or by reducing the biological oxygen demand (BOD), not directly by adding basic chemical substances.
- To eliminate pathogenic bacteria. is incorrect: The elimination of pathogenic bacteria is achieved through disinfection methods such as chlorination, ozonation, or UV treatment, rather than simple acid-base neutralization.
Key Takeaway: Factory wastes are treated with basic substances primarily to neutralize acids, preventing a drastic drop in the pH of water bodies that would otherwise be fatal to aquatic life.