What is the energy-related outcome of anaerobic digestion of sludge?

• A. It consumes energy without producing usable byproducts.
• B. It produces biogas, primarily methane, that can be used for energy.
• C. It produces only carbon dioxide with no energy value.
• D. It increases energy demand.

Answer: (D)

Anaerobic digestion yields energy through the production of biogas. Microorganisms break down the organic matter in sludge without oxygen, creating a gas mixture that is rich in methane. That methane can be burned to generate heat or electricity, or upgraded for use as renewable natural gas. So the process provides usable energy rather than simply consuming energy or producing only non-energy byproducts. While carbon dioxide is also produced, it doesn’t carry energy value, whereas the methane in biogas does. This makes energy recovery via biogas the key outcome of anaerobic digestion.