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CHAPTER 6

Bio-methanation (Anaerobic Digestion + Biogas)

Bio-methanation & Biogas

Anaerobic digestion of biodegradable waste to produce biogas (methane + CO2) — process design (continuous + batch, single-stage + two-stage), digester types (CSTR, plug-flow, dry-AD), feedstock characterisation, gas yield optimisation, biogas use (cooking, electricity, vehicle CNG via upgrading), digestate as fertiliser, integration with composting + WTE.

🔥 Biomethanation & BiogasManual on Municipal Solid Waste ManagementRevised Edition (2016) with SBM 2.0 (2021) + Plastic Waste / E-waste Rules updates

Key formulas

  • Biogas yield (m³/tonne wet waste) = function of feedstock, typically 60-100 for Indian MSW; 80-120 for food waste; 30-60 for mixed
  • Methane content of biogas = 55-65% typical (rest CO2 + trace H2S, NH3, H2O)
  • Energy content of biogas: 1 m³ ≈ 5.5-6.5 kWh thermal; ≈ 2-2.5 kWh electrical (after generator)
  • Hydraulic retention time HRT = Volume of digester / daily feed flow rate; typical 20-40 days for mesophilic
  • Loading rate (kg VS/m³/day) = (input × % VS) / digester volume; typical 1.5-3.5 for stable operation

Key values & thresholds

biogas yield food waste m3 per tonne
80 - 120
biogas yield mixed organic m3 per tonne
60 - 100
methane content pct
55 - 65
biogas energy thermal kWh per m3
5.5 - 6.5
biogas energy electrical kWh per m3
2.0 - 2.5 (with 35-40% engine efficiency)
digester HRT mesophilic days
20 - 40
digester HRT thermophilic days
15 - 25
digester temperature mesophilic C
30 - 38
digester temperature thermophilic C
50 - 55
loading rate typical kg VS m3 day
1.5 - 3.5
biogas plant capex INR crore per TPD
1 - 2.5 (varies with technology + scale)
compressed biogas CBG cost INR per kg
30 - 50 (raw biogas to vehicle CNG via PSA upgrading)
digestate fertiliser value INR per tonne wet
500 - 2000
go bardhan subsidy INR per tonne CBG
Variable (CGD compressed biogas under GOBARdhan / SATAT scheme)

Clause-level requirements

  • Biomethanation facility shall accept source-segregated wet waste; non-biodegradable shall not exceed 5 % by weight in feedstock.
  • Digester design (CSTR vs plug-flow vs dry-AD) shall be selected based on feedstock moisture, throughput, + operator capability.
  • Mesophilic operation (30-38°C) preferred for stability; thermophilic (50-55°C) for higher loading + faster destruction but operator-intensive.
  • Biogas use shall be specified upfront — cooking gas distribution, electricity generation, vehicle CNG (CBG) — affects upgrading + storage design.
  • Digestate (residue post-digestion) shall be processed: dewatering + composting OR direct application as fertiliser.
  • Pre-treatment (size reduction, contamination removal, de-packaging) shall be specified per feedstock type.
  • Safety: H2S removal upstream of any combustion or compression; biogas leak detection; flare for emergency.

Practitioner notes — what goes wrong in the field

  • Biomethanation is composting's complement — covers the same biodegradable fraction but produces gas + concentrated digestate fertiliser instead of compost.
  • Best feedstock: source-segregated kitchen / food waste (high moisture, high VS, biogas yield 80-120 m³/t). Garden waste alone gives lower yield (60-80 m³/t) — needs co-feed with food.
  • Digester types: CSTR (continuous stirred tank, most common for liquid/slurry); plug-flow (longer narrow reactor for higher solids); dry-AD (tunnel-type for high-solid, no slurry stage).
  • GOBARdhan (Galvanizing Organic Bio-Agro Resources Dhan): SBM 2.0 affiliated scheme funding rural + urban biogas plants. Subsidy up to 50% capex for community plants.
  • SATAT: PMO-launched mission to set up 5000 Compressed Bio-Gas (CBG) plants by 2030. Off-take guaranteed by oil companies (IOCL, BPCL, HPCL) at ₹46-54/kg CBG.
  • Indore Bijasan biogas plant (550 TPD, 1 MW power + 14000 m³/day biogas) is a model facility — sustained operation for 5+ years on source-segregated wet waste.
  • Biogas use options: (1) Cooking gas via local pipeline (institutional canteens, slum kitchens); (2) Electricity via gas engine (35-40% efficiency); (3) Compressed Bio-Gas (CBG) for vehicle CNG via PSA/membrane upgrading (₹30-50/kg cost; sells at ₹46-54/kg under SATAT).
  • Digestate management: 70-80 % water — needs dewatering (centrifuge, belt press) before further use. Solid fraction can be composted; liquid fraction concentrated to liquid fertiliser OR returned to soil.
  • H2S in biogas: 100-3000 ppm typical, corrosive + toxic. Iron sponge + biological scrubber + activated carbon for removal upstream of combustion or compression.
  • Capex (2026): community plant 0.5-5 TPD ₹50L-2cr; municipal 50-500 TPD ₹50-500cr; CBG-grade plant adds 25-40 % for upgrading + compression infrastructure.

FAQs

What's bio-methanation?
**Anaerobic digestion** of biodegradable waste to produce biogas (55-65% methane + 35-45% CO2 + trace H2S). Same wet waste fraction as composting (chapter 5) but produces fuel gas + concentrated digestate fertiliser instead of solid compost. Yield: 60-120 m³ biogas per tonne wet waste.
What can I do with the biogas?
Three main uses: (1) **Cooking gas** via local distribution to institutional canteens or slum kitchens; (2) **Electricity** via gas engine (1 m³ → ~2-2.5 kWh electrical at 35-40% efficiency); (3) **Compressed Bio-Gas (CBG)** as vehicle CNG via PSA/membrane upgrading — sold to oil companies under SATAT scheme at ₹46-54/kg.
What's GOBARdhan?
**Galvanizing Organic Bio-Agro Resources Dhan** — SBM 2.0 affiliated scheme funding rural + urban biogas plants. Up to 50% capex subsidy for community-scale plants. Targets 1500+ community biogas plants nationally by 2030. Indore Bijasan + Pune Hadapsar are urban examples.
What's SATAT?
**Sustainable Alternative Towards Affordable Transportation** — PMO-launched mission targeting 5000 Compressed Bio-Gas (CBG) plants by 2030. Off-take guaranteed by oil companies (IOCL, BPCL, HPCL) at ₹46-54/kg CBG. Major demand-side pull for urban biomethanation projects.
Should I do composting or biomethanation?
Both, in different proportions. **Biomethanation** for high-moisture food waste (yield is best); **composting** for garden + lower-moisture mixed organic. Many cities run both — 30-50% of wet to biomethanation, rest to composting. Choice depends on feedstock characterisation (chapter 1) + market for end-products.

Calculator

Bio-methanation Plant — Biogas Yield + Energy Output

↓ Download Excel

Compute biogas production + energy output for an anaerobic digestion plant given wet waste input + feedstock yield. Choose end-use (electricity via gas engine OR Compressed Bio-Gas via PSA upgrading for SATAT off-take). Best feedstock: source-segregated kitchen waste.

Inputs
Wet waste inputTPD
Biogas yieldm³/tonne
Food waste 80–120; mixed organic 60–100; garden 30–60
Methane content of biogas%
Gas engine electrical efficiency%
CBG upgrading efficiency (PSA)%
Methane recovery in CBG upgrading
SATAT CBG selling price₹/kg
Electricity feed-in tariff₹/kWh
Outputs
Biogas produced
10,000m³/day
TPD × yield
Methane (CH4) produced
6,000m³/day
biogas × CH4 %
Thermal energy potential
60,000kWh/day
biogas × ~6 kWh/m³ (LCV)
Electrical output (gas engine)
22,800kWh/day
thermal × engine_eff
Daily electricity revenue
1,25,400₹/day
Compressed Bio-Gas (CBG) yield
3,872kg/day
CH4 (m³) × 0.717 kg/m³ × upgrading_eff
Daily CBG revenue (SATAT)
1,93,590₹/day
CPHEEO Reference Values
Biogas yield (food waste)80 – 120 m³/tonne
Biogas yield (mixed)60 – 100 m³/tonne
Methane content typical55 – 65 %
Gas engine efficiency35 – 40 %
Energy 1 m³ biogas≈ 6 kWh thermal / 2.0–2.5 kWh electrical
SATAT CBG price₹46 – 54 / kg
GOBARdhan capex subsidyUp to 50 % (community plants)
Download the Excel version to keep a local copy with live formulas — change inputs in the sheet and outputs recompute automatically.

Cross-references

MNRE (Ministry of New & Renewable Energy) Biogas guidelinesGOBARdhan Scheme (SBM 2.0 affiliated)SATAT (Sustainable Alternative Towards Affordable Transportation) — compressed biogas missionMSW Rules 2016 (processing)PESO regulations — compressed gas safetyIS 16164:2014 (bio-methanation systems for organic waste)

Tags

biomethanationanaerobic digestionbiogascompressed biogasCBGGOBARdhanSATATdigesterwet waste energy

Engineer's notes

Bio-methanation is composting's energy-recovering complement. Both process the 50-60 % biodegradable fraction of MSW, but biomethanation produces fuel gas + concentrated digestate fertiliser instead of solid compost.

The process: source-segregated wet waste enters a sealed digester (CSTR or plug-flow), microorganisms break down organics in absence of oxygen over 20-40 day Hydraulic Retention Time (HRT), producing biogas (55-65 % methane, 35-45 % CO2, trace H2S/NH3/water vapour) + digestate (70-80 % water + organic residue + nutrients).

Yields depend on feedstock. Source-segregated food waste gives 80-120 m³ biogas per tonne wet weight; garden trimmings 60-80; mixed MSW with contamination 30-60. The methane fraction translates to roughly 2-2.5 kWh electrical per m³ via gas engine (35-40 % efficiency) or 5.5-6.5 kWh thermal.

Three biogas use options:

1. Cooking gas — local distribution to institutional canteens, slum kitchens, schools. Lowest infrastructure cost; immediate community benefit.

2. Electricity — gas engine + grid feed-in. Standard technology; 35-40 % efficiency means ~2 kWh per m³.

3. Compressed Bio-Gas (CBG) — upgraded to ≥ 95 % methane via PSA/membrane scrubbing, compressed to 250 bar, sold as vehicle CNG. Costs ₹30-50/kg to produce; sells at ₹46-54/kg under SATAT scheme. The most lucrative use, unlocked by SATAT off-take guarantee.

The Indian policy stack: GOBARdhan (SBM 2.0 affiliated, up to 50 % capex subsidy for community plants) + SATAT (5000 CBG plants by 2030 target, off-take guaranteed by oil companies). Together they provide both supply-side capex support + demand-side off-take guarantee — strong policy framework.

Reference operating plant: Indore Bijasan (550 TPD, 1 MW power + 14000 m³/day biogas + sustained 5+ years on source-segregated wet waste) is the urban India model. Pune Hadapsar, Hyderabad Jawaharnagar, Mumbai Deonar smaller-scale operations. Several SATAT CBG plants commissioned 2024-26.

Digestate management is the often-overlooked part. The 70-80 % water content needs dewatering (centrifuge, belt press) before use. Solid fraction can be composted; liquid concentrated to liquid fertiliser OR applied directly to soil.

Cost reality (2026): community-scale plant (0.5-5 TPD) ₹50 lakh - 2 crore capex; municipal (50-500 TPD) ₹50-500 crore. CBG-grade upgrading + compression adds 25-40 %. Tipping fee revenue + biogas/CBG sale + digestate sale can make plants self-funding at 50+ TPD scale.

Where this chapter sits: biomethanation + composting (chapter 5) between them should handle 90 %+ of the biodegradable fraction. Choosing the mix depends on feedstock characterisation (chapter 1) + local demand for biogas/CBG/compost. Many cities run both — typically 30-50 % of wet waste to biomethanation, rest to composting.

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Manual on Municipal Solid Waste Management · Revised Edition (2016) with SBM 2.0 (2021) + Plastic Waste / E-waste Rules updates · Central Public Health and Environmental Engineering Organisation (CPHEEO), Ministry of Housing and Urban Affairs, Government of India.
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