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Biogas plants under Clean Development Mechanism

Short answer

Biogas plants reduce emissions by displacing firewood and fossil fuels, preventing deforestation, capturing methane from dung (which otherwise would be released) and burning it to biogenic CO₂, substituting chemical fertilizers with bio-slurry. Methane has 25-28 times the GWP of CO₂, so capturing it yields significant emission reductions.

Biogas plants of Nepal are registered as Clean Development Mechanism project because of its contribution for reducing greenhouse gas emission. How would you argue that the biogas plants are contributing to reduce greenhouse gas emission?

Biogas is a gas (about 55–65% methane, CH₄, and 35–45% CO₂) produced by anaerobic digestion of cattle dung and other organic waste. Nepal's household biogas programme (Biogas Support Programme, with AEPC) was among the first CDM projects registered with the UNFCCC from Nepal (2005) and earns carbon credits (CERs) for emission reduction.

How biogas plants reduce greenhouse gas emissions

  1. Replacing firewood – each household plant replaces a large amount of firewood each year. Less forest is cut, so the forest keeps absorbing CO₂ (carbon sink protected). Firewood from unsustainable harvest adds net CO₂.
  2. Replacing fossil fuels – biogas replaces kerosene and LPG used for cooking and lighting, avoiding CO₂ from fossil carbon.
  3. Capturing methane from dung – dung left in heaps or open pits decomposes and releases methane. Methane has a global warming potential about 25–28 times that of CO₂ over 100 years. In a sealed digester this methane is captured and burnt:
CH4+2O2→CO2+2H2O\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

Burning converts a strong GHG into CO₂, which is biogenic (carbon neutral). 4. Carbon neutral fuel – CO₂ from burning biogas came from plants eaten by cattle, so there is no net addition. 5. Bio-slurry as fertiliser – reduces use of chemical fertiliser, whose manufacture emits CO₂ and N₂O. 6. Cleaner combustion – less black carbon and smoke compared to traditional stoves.

Cycle

 Grass/fodder --> Cattle --> Dung --> Digester --> Biogas
      ^                                  |          |
      |                               Slurry      Burn
      |                              (manure)       |
      +------------- CO2 absorbed <------ CO2 <-----+

Co-benefits counted under CDM

  • Reduced indoor air pollution and better health.
  • Time saved in firewood collection, mainly for women.
  • Revenue from CERs helps subsidise more plants.

Hence biogas plants reduce GHG emission both by avoiding methane release and by displacing firewood and fossil fuel, which justifies their CDM registration.

✓ Answer checked by Claude Opus 5.5 (high effort)

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