Which process decomposes waste under anaerobic conditions to produce biogas and a compost-like residue?

• A. Anoxic
• B. Anaerobic digestion
• C. Baffle
• D. Algae

Answer: (B)

Decomposing waste in the absence of oxygen by microbes that produce methane-rich biogas and a solid digestate is anaerobic digestion. In sealed digesters, organic matter is broken down without oxygen, and methanogenic microbes generate biogas (mostly methane and carbon dioxide) while leaving behind a compost-like residue called digestate. This process stabilizes wastewater solids and allows energy recovery from the waste. Anoxic refers to environments without oxygen used mainly for nitrogen removal, not for producing biogas. A baffle is just a flow-directing plate in a tank, not a biological process. Algae are photosynthetic organisms, not the microbial digestion process described here.