---
title: "Bio-energy with an example"
subject: "Power Plant Design"
chapter: 1
key: "semester_8/power_plant_design:bio-energy-example"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/bio-energy-example
site: BCT Engineering
---

# Bio-energy with an example

Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation

- Asked in: 2072 Asoj, 6 marks
- Video: [Biomass Energy](https://www.youtube.com/watch?v=Cux0Xwvy0cU) — Najam Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/bio-energy-example
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1

## Question

What is bio-energy? Describe with a suitable example.

## Short answer

Bio-energy is energy from organic matter like wood, dung, or crop residues. A common example is a household biogas plant: cattle dung mixed with water ferments in an airtight digester, producing methane for cooking and slurry for fertilizer, reducing firewood use and indoor smoke.

## Answer

**Bio-energy** is the energy obtained from biomass, i.e. organic matter from plants and animals (wood, crop residue, dung, energy crops, food and municipal organic waste). It is stored solar energy, captured by photosynthesis, and is renewable if used sustainably.

#### Forms of bio-energy
| Form | Process | Product |
|---|---|---|
| Solid | Direct combustion, briquetting | Heat, steam for power |
| Gaseous | Anaerobic digestion | Biogas (CH₄ + CO₂) |
| Gaseous | Gasification (partial oxidation) | Producer gas (CO, H₂) |
| Liquid | Fermentation | Bio-ethanol |
| Liquid | Transesterification | Bio-diesel (from jatropha etc.) |

#### Example: household biogas plant (Nepal)
Nepal has several hundred thousand family-size biogas plants (mainly GGC-2047 fixed dome design) promoted by AEPC and the Biogas Support Programme.

```text
 Dung+water -> Inlet -> Digester (dome) -> Gas pipe
                           |                  |
                      Outlet tank        Stove / lamp
                           |
                   Slurry (fertiliser)
```
**Working:**
1. Fresh cattle dung is mixed with water (about 1:1) and fed through the inlet.
2. In the airtight digester, bacteria break down the organic matter without oxygen in three stages: hydrolysis, acid formation and methane formation.
3. Gas (about 60% methane) collects in the dome and flows through a pipe to the stove.
4. Digested slurry comes out of the outlet and is used as manure.

**Benefits:**
- Replaces firewood and kerosene; saves forest.
- Smoke-free kitchen and better health.
- Good organic fertiliser.
- Reduces GHG emission (registered under CDM).

#### Other examples
- Bagasse-based power in sugar mills.
- Rice husk gasifier for power in rice mills.
- Improved cook stoves burning firewood more efficiently.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Bio-energy is
   A. Energy from biomass, stored solar energy captured by photosynthesis
   B. Energy from uranium
   C. Energy from tides
   D. Energy from coal only
   Answer: A. Bio-energy comes from organic matter of plants and animals. (Key point: Definition)

2. How is biogas produced in the digester?
   A. Bacteria break down organic matter without oxygen in hydrolysis, acid formation and methane formation
   B. Dung is burnt with air
   C. Dung is dried in sunlight
   D. Dung is electrolysed
   Answer: A. Anaerobic digestion in three stages gives gas with about 60% methane. (Key point: Digester working)

3. Which process gives bio-ethanol?
   A. Gasification
   B. Transesterification
   C. Fermentation
   D. Briquetting
   Answer: C. Fermentation gives ethanol; transesterification gives bio-diesel. (Key point: Forms of bio-energy)

4. Which is a benefit of household biogas?
   A. More smoke
   B. Outlet slurry gives organic fertiliser and saves firewood
   C. Needs oxygen
   D. Uses more kerosene
   Answer: B. Biogas replaces firewood and kerosene, gives a smoke-free kitchen and slurry manure. (Key point: Biogas benefits)

## Related in Power Plant Design

- [Biomass compared with geothermal energy](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abioenergy-vs-geothermal) — Power Plant Design, chapter 1
- [Biomass and the carbon neutral cycle](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abiomass-carbon-neutral-cycle) — Power Plant Design, chapter 1
- [Conventional, non-conventional sources and biomass](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-biomass) — Power Plant Design, chapter 1

## Related in other subjects

- [Synthetic fuel from biomass, bio fuel cells](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asynthetic-fuel-biofuel-cell) — Energy Environment and Society, chapter 3
- [Bio-chemical conversion of biomass](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiochemical-conversion-biomass) — Energy Environment and Society, chapter 3