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CHAPTER 5

Composting — Aerobic, Vermi, In-Vessel

Composting (Aerobic, Vermi, In-vessel)

Aerobic decomposition of biodegradable waste — windrow composting (open / covered), in-vessel reactors (continuous + batch), vermi-composting (earthworms), integrated bio-CNG plants. Process design, operating parameters (C/N ratio, moisture, temperature, turning frequency), product quality standards, market for compost, integration with city waste flow.

🌱 Composting (Aerobic / Vermi)Manual on Municipal Solid Waste ManagementRevised Edition (2016) with SBM 2.0 (2021) + Plastic Waste / E-waste Rules updates

Key formulas

  • Compost yield = input wet weight × (1 − moisture loss × 0.45) × (1 − stabilisation loss × 0.30); typical 30-40% of input by weight
  • C/N ratio target: 25:1 to 30:1 input; ~15:1 to 20:1 finished
  • Windrow turning: every 3-7 days for first 4 weeks; weekly thereafter; total 60-90 days
  • In-vessel residence time: 2-4 weeks (vs 60-90 days windrow)
  • Vermi yield: 60-70% of input weight as vermicompost (slower process but higher value)

Key values & thresholds

windrow typical dimensions m
Width 2.5-3.5, height 1.5-2.0, length 30-50
windrow throughput TPD
10 - 50 typical (per pad)
windrow capex INR crore per 50TPD
1 - 3
windrow om INR per tonne
300 - 800
windrow compost cycle days
60 - 90
in vessel residence days
14 - 28
in vessel capex INR crore per 50TPD
5 - 12
vermi compost cycle days
90 - 120
vermi capex INR lakh per TPD
2 - 5
compost C N ratio input target
25:1 to 30:1
compost moisture target pct
50 - 60 (turning trigger > 65 or < 40)
compost temp thermophilic C
55 - 65 (kills pathogens + weed seeds)
compost FCO grade min organic carbon pct
12 % (Fertiliser Control Order spec)
compost FCO grade max moisture pct
25 %
compost market price FCO grade INR per kg
3 - 8
city compost subsidy MRTS INR per kg
1.5 (Market Rationalisation Subsidy under SBM)

Clause-level requirements

  • Composting facility shall accept only source-segregated wet waste; mixed waste shall not be accepted (heavy metal contamination + glass + plastic ruins compost).
  • Windrow composting shall be on impervious pad with leachate collection + roof (covered) for monsoon.
  • Compost cycle: minimum 60 days windrow OR equivalent in-vessel/vermi process.
  • Finished compost shall meet Fertiliser Control Order (FCO) specification: ≥ 12% organic carbon, ≤ 25% moisture, C/N ≤ 20:1, heavy metals within limits.
  • Compost output shall be marketed via MRTS (Market Rationalisation Subsidy) at ₹1.5/kg subsidy under SBM 2.0; for direct sale, ₹3-8/kg typical.
  • Pathogen kill: temperature ≥ 55-65°C for ≥ 3 consecutive days during thermophilic phase (kills E. coli, Salmonella, weed seeds).

Practitioner notes — what goes wrong in the field

  • Composting works best on source-segregated wet waste. Mixed-waste composting (legacy 1990s practice) yields contaminated low-grade compost that doesn't sell + doesn't meet FCO.
  • Windrow is the workhorse — 80 % of Indian city compost facilities. Open windrow during dry season, covered/roofed for monsoon (uncovered windrow gets waterlogged + anaerobic).
  • In-vessel (rotary drum, tunnel reactor) gives 2-4 week processing vs 60-90 days windrow — useful where land is scarce or for high-value products. Higher capex.
  • Vermicomposting (earthworm-based): slower (90-120 days) but higher value product (₹8-15/kg vs ₹3-8/kg windrow). Best for source-segregated kitchen waste in housing societies + apartment complexes.
  • Bulk generators (apartment complexes, hotels, malls) increasingly install on-site composters — 0.5-2 TPD scale. Pays back in 3-5 years through tipping fee avoidance + compost sale.
  • Compost market: cement co-processing? No (calorific value too low). Agriculture? Yes — but farmers prefer chemical fertiliser; need MRTS subsidy + sustained sales effort.
  • MRTS (Market Rationalisation Subsidy) under SBM: ₹1500/tonne (₹1.5/kg) compost subsidy paid to retailers — incentivises sale + reduces gap with chemical fertiliser. Released through dedicated DBT mechanism.
  • Indore, Pune, Bhopal have functional compost markets (compost sells out routinely). Many other cities have compost piling up unsold — usually due to mixed-waste origin + no marketing.
  • Heavy metals: even source-segregated wet waste accumulates trace metals from food packaging, ink, paper. Periodic testing per FCO (Cd, Cr, Pb, Hg, Ni, As limits).
  • Compost cycle: thermophilic phase (55-65°C, 5-10 days) → mesophilic (45-50°C, 10-20 days) → curing (ambient, 30-45 days). Total 60-90 days for FCO-grade.
  • Carbon-Nitrogen ratio: C/N input target 25-30:1. Excess N (only food waste) → ammonia stink. Excess C (only garden trimming) → slow process. Mix food + garden + paper/wood chips for balance.

FAQs

What's the difference between windrow, in-vessel, and vermi composting?
**Windrow** = open/covered piles, 60-90 day cycle, 80% of Indian capacity. Cheap (₹1-3 cr per 50 TPD) but land-hungry. **In-vessel** = closed reactors (drum, tunnel), 14-28 days, higher capex (₹5-12 cr per 50 TPD), saves land. **Vermicomposting** = earthworms, 90-120 days, slow but premium product (₹8-15/kg).
What is FCO-grade compost?
**Fertiliser Control Order** (FCO) specification — the legal standard for compost marketed in India. Requires ≥ 12 % organic carbon, ≤ 25 % moisture, C/N ratio ≤ 20:1, heavy metals (Cd, Cr, Pb, Hg, Ni, As) within limits. Without FCO certification, compost cannot be sold legally.
Why does my city compost not sell?
Common reasons: (1) Mixed-waste origin → low grade, contamination, unattractive product. (2) No marketing effort + sales channel. (3) Farmers prefer chemical fertiliser (subsidised). Solution: source-segregated wet only, FCO-certify, leverage MRTS subsidy (₹1.5/kg), build agricultural retail relationships. Indore, Pune, Bhopal cracked this.
What's MRTS?
**Market Rationalisation Subsidy** under SBM 2.0 — ₹1500/tonne (₹1.5/kg) subsidy paid to retailers selling FCO-grade city compost, transferred via DBT. Reduces price gap with chemical fertiliser + incentivises retail uptake. Eligible compost facilities must produce + market FCO-grade product.
Can apartment complexes do their own composting?
Yes — increasingly mandatory under SBM 2.0 for complexes > 100 units. On-site composter (windrow shed, drum, vermi) at 0.5-2 TPD scale typical. Capex ₹2-15 lakh, pays back in 3-5 years through tipping fee avoidance + compost sale to gardens/landscaping. Bengaluru, Pune, Mumbai mandate this.

Cross-references

Fertiliser Control Order (FCO) 1985 + amendments — compost specificationMSW Rules 2016 (Schedule II — processing)SBM 2.0 (MRTS subsidy framework)MoHUA Compost Marketing Cell guidelinesIS 16556 (compost from MSW — specification)CPCB Composting Guidelines

Tags

compostingwindrowin-vessel compostervermicompostingFCO grade compostwet waste processingaerobic decompositionC N ratiocity compost

Engineer's notes

Composting is the natural processing route for the 50-60 % biodegradable fraction of Indian MSW. Done well, it converts a problem (rotting waste, methane emissions, landfill pressure) into a product (organic fertiliser worth ₹3-15/kg).

Three technology options dominate Indian practice:

1. Windrow composting is the workhorse — ~80 % of city composting capacity. Open piles 2.5-3.5 m wide, 1.5-2 m high, 30-50 m long, on impervious pad with leachate collection. 60-90 day cycle. Capex ₹1-3 crore per 50 TPD. Land-hungry but cheap.

2. In-vessel composting uses closed reactors (rotary drums, tunnel reactors) for 14-28 day processing. Higher capex (₹5-12 crore per 50 TPD) but saves land + better odour control + faster cycle. Useful where land is scarce or high-value product needed.

3. Vermicomposting uses earthworms (Eisenia fetida primarily) over 90-120 days. Slower but produces premium product (₹8-15/kg vs ₹3-8/kg windrow). Best for source-segregated kitchen waste in housing societies + apartment complexes.

The make-or-break input: source-segregated wet waste only. Mixed-waste composting (legacy 1990s practice) yields contaminated low-grade product that doesn't meet FCO + doesn't sell + ends up dumped. Get segregation right (chapter 2) before scaling composting.

The make-or-break output: a functioning compost market. Without market, FCO-grade compost piles up at the facility. Indore, Pune, Bhopal have cracked this — sustained agricultural retailer relationships, MRTS subsidy leveraging, brand visibility, organic-farming partnerships. Many other cities have compost mountains — usually mixed-waste origin + no marketing.

MRTS (Market Rationalisation Subsidy) under SBM 2.0 pays ₹1500/tonne (₹1.5/kg) to retailers selling FCO-grade city compost, transferred via DBT. This narrows the price gap with subsidised chemical fertiliser + incentivises retail uptake.

Process control matters: C/N ratio 25-30:1 input (mix food + garden + paper to balance), moisture 50-60 % (turn at 65 % +, water at 40 % -), thermophilic temperature 55-65 °C for ≥ 3 days (pathogen kill), turning every 3-7 days for first month then weekly. Total cycle 60-90 days.

Bulk generator on-site composting is the rising frontier. Apartment complexes > 100 units increasingly mandate on-site composting under SBM 2.0 — 0.5-2 TPD scale, ₹2-15 lakh capex, pays back in 3-5 years.

Where this chapter sits: composting handles the 50-60 % biodegradable bulk of MSW. Without it, this fraction either lands in landfills (bad — methane + leachate + space waste) or in biomethanation (alternative — covered in chapter 6). Composting + biomethanation between them should handle 90 % + of biodegradable input.

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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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