--- title: "Biomass and conversion routes" subject: "Energy Environment and Society" chapter: 3 key: "semester_7/energy_environment_and_society:biomass-conversion-routes" source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/biomass-conversion-routes site: BCT Engineering --- # Biomass and conversion routes Energy Environment and Society · Chapter 3: Renewable Energy Sources - Asked in: 2074 Asoj, 1+3 marks; 2072 Kartik, 1+3 marks; 2070 Asar, 2+2 marks; year not given (asked 3 times) - Video: [Types of Biofuels, Energy conversion routes from biomass](https://www.youtube.com/watch?v=2ZG2CyknGCg) — Vidya-mitra - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/biomass-conversion-routes - Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3 ## Question What is biomass (biogas)? List any four major routes for the conversion of biomass to energy and other useful products. Describe its potential. ## Short answer Biomass is organic matter used as fuel; biogas is mainly methane and CO2 produced by anaerobic digestion. Major conversion routes are direct combustion, gasification and pyrolysis, anaerobic digestion and fermentation, and esterification or briquetting. Biomass provides about 10% of world primary energy and about 60-65% of Nepal's total energy. ## Answer **Biomass** is organic matter of plant or animal origin, such as wood, crop residues, animal dung, food waste, municipal waste and energy crops, that can be used as fuel. **Biogas** is a mixture of about 55–65% methane (CH₄), 35–45% CO₂ and traces of H₂S, produced when organic matter, for example cattle dung, is digested by bacteria without oxygen (anaerobic digestion). #### Four major conversion routes 1. **Direct combustion:** burning wood, residue or briquettes for heat, cooking, steam and electricity. 2. **Thermo-chemical conversion:** gasification (producer gas), pyrolysis (bio-oil, charcoal, gas) and carbonisation. 3. **Bio-chemical conversion:** anaerobic digestion (biogas) and fermentation (ethanol from sugar and starch crops). 4. **Chemical / mechanical extraction:** transesterification of vegetable oils (jatropha, used cooking oil) to biodiesel; also briquetting / densification. ```text Biomass --+--> Combustion ------> Heat, power +--> Gasification/pyrolysis -> Gas, oil, char +--> Digestion ------> Biogas + slurry +--> Fermentation ---> Ethanol +--> Esterification -> Biodiesel ``` #### Potential - **World:** biomass is the fourth largest energy source and gives about 10% of world primary energy, mostly in developing countries. - **Nepal:** biomass (firewood, dung, residues) supplies about 60–65% of total energy. Biogas potential is estimated at 1.9 million household plants, of which over 400,000 have been installed with support from AEPC (previously the Biogas Support Programme). Other potential: institutional and municipal biogas, briquettes from forest residue and invasive species (*Banmara*), biodiesel from jatropha, and ethanol from sugar-cane molasses. - **Benefits:** reduces firewood use and deforestation, indoor smoke and greenhouse gas emissions (CDM credits), and gives rich organic fertiliser (slurry). - Biogas is limited mainly by the availability of livestock in the hills and by temperature (it works poorly in cold areas). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is biogas mainly composed of? A. Mostly hydrogen and nitrogen B. About 55-65% methane and 35-45% CO2 C. Mostly carbon monoxide D. Mostly oxygen and CO2 Answer: B. Biogas from anaerobic digestion is mainly methane with CO2 and traces of H2S. (Key point: Biogas composition) 2. Under what condition is biogas produced? A. Bacteria digest organic matter without oxygen B. Burning organic matter in excess air C. Heating wood in a vacuum to give charcoal D. Fermentation of sugar to ethanol Answer: A. Biogas is produced by anaerobic digestion, which is bio-chemical conversion. (Key point: Anaerobic digestion) 3. Which pair is correctly matched route to product? A. Gasification gives ethanol B. Fermentation gives producer gas C. Direct combustion gives biodiesel D. Transesterification of vegetable oil gives biodiesel Answer: D. Transesterification of oils like jatropha yields biodiesel; gasification gives gas and fermentation gives ethanol. (Key point: Conversion routes) 4. What limits biogas use in Nepal? A. Lack of any organic waste B. Biogas produces no fertiliser C. Livestock availability in hills and poor performance in cold areas D. Biogas causes more deforestation Answer: C. Biogas needs enough livestock dung and warm temperature for digestion. (Key point: Biogas limits) ## Related in Energy Environment and Society - [Biogas routes and climate change](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiogas-routes-climate-change) — Energy Environment and Society, chapter 3 - [Biomass conversion, IV curve, wind mapping](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiomass-iv-curve-wind-mapping) — Energy Environment and Society, chapter 3 - [Thermo-chemical conversion of biomass](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Athermochemical-conversion-biomass) — 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 ## Related in other subjects - [Short note: Biomass to biogas](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Abiomass-to-biogas) — Technology, Environment and Society, chapter 6 - [Biochemical conversion of biomass to fuels](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Abiomass-biochemical-conversion) — Energy Resources, chapter 3 - [Advantages of electrical energy over other forms](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aadvantages-electrical-energy-other-forms) — Utilization of Electrical Energy, chapter 1, asked 2× - [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