Respiration in Organisms

UPSC GS3 — Fermentation:

What is fermentation? Anaerobic respiration by microorganisms (mainly yeast and bacteria) — producing useful products.

Types of fermentation:

1. Alcoholic fermentation (yeast): Glucose → ethanol + CO₂

   • Bread making: CO₂ makes dough rise (bubbles expand in heat → spongy texture)
   • Beer, wine, whisky making: Ethanol is the desired product
   • Bioethanol production: Sugarcane molasses/corn fermented by yeast → ethanol → added to petrol (E10, E20 blends); India's Ethanol Blended Petrol (EBP) Programme — target 20% ethanol blending by 2025–26

2. Lactic acid fermentation (bacteria):

   • Yogurt/curd (dahi): Lactobacillus bacteria ferment milk lactose → lactic acid → sours milk → sets as curd
   • Cheese: Different bacteria/molds for different cheese types
   • Idli/dosa: Batter fermented by natural bacteria → lactic acid → sour flavour
   • Sauerkraut, kimchi, pickles

3. Acetic acid fermentation:

   • Acetobacter bacteria convert ethanol → acetic acid (vinegar)

Biogas (anaerobic digestion):

• Organic waste (cow dung, agricultural waste, food waste) → anaerobic bacteria → methane (CH₄) + CO₂ + digestate
• Methane collected and used as fuel (cooking, electricity)
• India's biogas sector:
  • National Biogas and Manure Management Programme (NBMMP): Household biogas plants from cattle dung
  • Compressed Biogas (CBG): Industrial scale; SATAT scheme originally targeted 5,000 CBG plants by 2023-24 — target massively missed; only ~108 plants operational by 2025 (scale-up ongoing)
  • MSW-based biogas plants at city level

Ethanol blending programme:

• India achieved ~17.98% ethanol blending in petrol in ESY 2024-25 (up to February 2025) — Ministry of Petroleum & Natural Gas / PIB
• Up from just 2% in 2014 — a major energy transition achievement
• India crossed E20 (20% ethanol blending) in 2025, ahead of the 2025-26 deadline; E20 mandated nationwide from April 1, 2026
• Reduces fossil fuel import bill; reduces CO₂ emissions
• Source: Sugarcane (B-heavy molasses, C-molasses, sugarcane juice) + food grain surpluses (rice, maize)
• Beyond E20: Government exploring E22, E25 for flex-fuel vehicles in coming years

[Additional] India's EBP, E20, and PM JI-VAN Yojana (GS3 — Energy / Environment / Agriculture):

Ethanol blending — progression (official MoPNG/PIB data):

E20 petrol already dispensed at 17,400+ retail outlets across India ahead of the mandate.

National Policy on Biofuels 2018 — key facts:

Ethanol feedstocks used in India:

National benefits — cumulative (10 years, as of December 2024):

PM JI-VAN Yojana — 2G ethanol (key facts):

Why 2G ethanol matters (GS3 Mains angle): 1G ethanol uses food crops (sugarcane, rice) — creates food vs fuel conflict. 2G ethanol uses agricultural waste (rice straw = main cause of stubble burning in Punjab/Haryana) — simultaneously addresses air pollution (stubble burning), energy security (less crude oil import), and farmer income (stubble becomes a saleable raw material instead of being burnt).

UPSC synthesis: EBP = GS3 Energy + Environment. Key exam facts: EBP 2024-25 = 17.98% blending; E20 mandated nationwide = April 1, 2026; National Policy on Biofuels = 2018 (amended 2022 to advance E20 from 2030 to ESY 2025-26); 10-year forex savings = Rs. 1,13,007 crore; CO₂ reduction = 557 lakh MT; PM JI-VAN = notified March 2019 = Rs. 1,969.50 crore = extended to 2028-29 = first plant at Panipat (IOC), August 10, 2022 = 2G ethanol from agricultural residues. Prelims trap: ESY (Ethanol Supply Year) runs November to October (NOT January to December — targets and achievements are reported per ESY, not per financial year; this matters when comparing years); 2G ethanol feedstock = agricultural residues (NOT sugarcane or food grains — those are 1G; 2G uses straw, bagasse, cellulosic biomass); E20 mandate date = April 1, 2026 (NOT April 1, 2025 — frequently confused; E20 is the 20% mandate nationwide from April 2026); PM JI-VAN = Ministry of Petroleum and Natural Gas (NOT Ministry of Agriculture — agriculture provides the feedstock but the scheme is under MoPNG).

[Additional] GOBAR-DHAN and India's Biogas Sector (GS3 — Environment / Energy / Agriculture):

Biogas — the chemistry (anaerobic digestion):

Organic matter (dung/food waste) → Anaerobic bacteria → CH₄ (55–65%) + CO₂ (35–45%) + bio-slurry

• The process occurs without oxygen (anaerobic) — bacteria break down complex organic molecules
• Bio-slurry (digestate) = excellent organic fertiliser; enriched in nitrogen, phosphorus, potassium
• The biogas replaces LPG or firewood → reduces indoor air pollution; reduces deforestation pressure

GOBAR-DHAN scheme — key data:

Biogas vs Compressed BioGas (CBG):

India's three-tier biogas programme structure:

Why SATAT targets were missed:

• High capital cost of purification/compression equipment
• Feedstock aggregation challenges (collecting enough biomass)
• Grid connectivity and offtake agreement issues
• Only ~106 CBG plants operational vs 5,000 target (December 2023 deadline)

Transport sector and biofuel opportunity:

• Transport = ~12% of India's energy-related CO₂ emissions
• Road transport = 94% of transport CO₂
• EBP (ethanol) + CBG (biogas as CNG substitute) together = India's dual biofuel strategy for transport decarbonisation

UPSC synthesis: GOBAR-DHAN + biogas = GS3 Environment + Energy. Key exam facts: GOBAR-DHAN = launched 2018 = Swachh Bharat Mission Grameen Phase-II = Ministry of Jal Shakti = inputs: cattle dung + kitchen/market/crop waste = outputs: biogas + bio-slurry; biogas = ~55-65% methane (CH₄) = anaerobic process; CBG = compressed purified biogas = replaces CNG; SATAT = target 5,000 CBG plants = target missed (~106 operational by 2025); Budget 2023 = 500 waste-to-wealth plants + Rs. 10,000 crore; transport = 12% of India's energy CO₂; road = 94% of transport CO₂. Prelims trap: GOBAR-DHAN is under Ministry of Jal Shakti (NOT Ministry of New and Renewable Energy — MNRE runs the National Biogas Programme; GOBAR-DHAN is under Jal Shakti via SBM-G); biogas is primarily methane (NOT hydrogen — a common confusion; biogas = CH₄ + CO₂; hydrogen is a different fuel); SATAT target = 5,000 plants (NOT 500 — the Budget 2023 announced 500 waste-to-wealth plants, but SATAT's original target was 5,000 CBG plants — two different numbers); bio-slurry from biogas plants is a fertiliser (NOT a waste — it is nutrient-rich digestate, a key co-product that improves soil health).