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What is the composition of activated sludge?

  1. A single type of microorganism

  2. A mixture of various microorganisms

  3. Only aerobic bacteria

  4. Purely anaerobic microorganisms

The correct answer is: A mixture of various microorganisms

Activated sludge is composed of a diverse mixture of various microorganisms. This community typically includes bacteria, protozoa, and sometimes filamentous organisms. The mixture works synergistically to break down organic matter in wastewater during the treatment process. Having a diverse microbial population is crucial for effective treatment; different microorganisms have unique metabolic pathways that allow them to degrade different types of waste. The presence of various species can also help stabilize the treatment process by providing resilience against fluctuations in the composition of the influent wastewater. While some choices suggest a limited type of microorganism, activated sludge is specifically designed to harness the benefits of a varied microbial community to improve treatment efficiency, nutrient removal, and overall performance of the wastewater treatment process.