Correct Option
The correct option is Biogas : Produced by anaerobic degradation
Explanation
Biological waste treatment relies on the metabolic activities of microorganisms to decompose organic matter. These processes are primarily categorized based on the requirement of oxygen: aerobic processes (requiring oxygen) and anaerobic processes (occurring in the absence of oxygen).
Option-wise Analysis
- Option (a) is Incorrect: Aerobic bacteria are microorganisms that require oxygen for cellular respiration and growth. They function effectively only in the presence of air (oxygen) and are used in processes like the activated sludge system.
- Option (b) is Incorrect: Anaerobic bacteria function in the absence of oxygen. They decompose organic matter in oxygen-free environments. The presence of air (oxygen) often inhibits their activity or can be toxic to strict anaerobes.
- Option (c) is Correct: Biogas is a renewable energy source produced by the anaerobic degradation (digestion) of organic matter such as agricultural waste, manure, municipal waste, and plant material. Methanogenic bacteria break down this biomass in an oxygen-free environment to release gases like methane and carbon dioxide.
- Option (d) is Incorrect: Activated sludge is a key component of secondary wastewater treatment. It consists of a flocculated mass of aerobic bacteria, fungi, and protozoa mixed with wastewater. It is rich in organic biological mass used to digest pollutants, rather than being composed of inorganic metals only.
Key Takeaway
Biogas production is an anaerobic process yielding methane, whereas the activated sludge process is an aerobic method used in sewage treatment to reduce organic load.