Civil Engineering MCQAE Level Civil Engineering

In anaerobic sludge digestion, the biogas produced contains approximately:

Environmental EngineeringAnaerobic Digestion BiogasMEDIUM

Choose the correct answer

A

90% CO2, 10% CH4

B

60-70% methane (CH4) and 30-40% CO2 with traces of H2S

C

50% H2 and 50% CH4

D

100% methane

Correct Answer

B. 60-70% methane (CH4) and 30-40% CO2 with traces of H2S

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Biogas composition from anaerobic digestion: ~65% CH4, ~35% CO2, traces H2S and N2. Calorific value ~5500 kcal/m3. Gas yield: 0.5-0.9 m3 per kg VSS destroyed. Two-stage digestion: primary (mesophilic, 35 deg C) for gas production; secondary for thickening/storage.

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