Unlocking the Potential of Co-Composting in India's Waste Management Landscape
India's push towards sustainable sanitation has accelerated under initiatives like the Swachh Bharat Mission, leading to a surge in Faecal Sludge Treatment Plants (FSTPs). These facilities process sludge from on-site sanitation systems such as septic tanks and pit latrines, producing nutrient-rich biosolids—semi-solid residues left after treatment. However, managing these biosolids remains a bottleneck, with much of it stockpiled or landfilled, posing environmental risks.
The Centre for Science and Environment (CSE), a leading policy research institute, recently released its report titled 'From Waste to Resource: Co-Composting Practices in India and Bangladesh' on March 2, 2026. This document spotlights co-composting as a transformative solution. Co-composting involves mixing biosolids with municipal organic waste—like kitchen scraps and garden trimmings—to create high-quality compost suitable for agriculture. This process not only diverts waste from landfills but also enriches soil fertility in a country where organic fertilizers are in high demand.
What is Co-Composting? A Step-by-Step Breakdown
Co-composting leverages the natural decomposition of organic materials accelerated by microorganisms. Here's how it works in practice, as detailed in CSE's case studies using the windrow method—the most common decentralized approach in India:
- Collection and Preparation: Treated biosolids from FSTPs are dewatered and mixed with source-segregated organic waste in ratios typically ranging from 1:2 to 1:4 (biosolids to organic waste) to achieve an optimal carbon-to-nitrogen (C:N) ratio of 25-30:1.
- Pile Formation: Materials are layered in long rows or windrows on paved beds, often 8x4x5 feet in size, with periodic turning to aerate.
- Decomposition Phase: Piles heat up to 65-70°C over 30-35 days, killing pathogens like E. coli and helminth eggs through thermophilic activity.
- Maturation: Cooled compost matures for 45-80 days, developing stable humus; final sieving and grinding produce marketable granules.
- Quality Testing: Samples are analyzed against Fertilizer Control Order (FCO) standards for nutrients, heavy metals, and pathogens.
This aerobic process reduces volume by 50-70%, minimizes odors, and yields a product richer in nitrogen, phosphorus, and potassium than single-source composts.
India's Faecal Sludge Crisis: Scale and Urgency
India boasts over 1,034 FSTPs generating about 250 tonnes of biosolids daily, a direct outcome of Swachh Bharat Mission's focus on sanitation coverage. Yet, 67% goes unused, contributing to methane emissions and groundwater contamination. Meanwhile, municipal solid waste (MSW) hits 62 million tonnes annually, with 50% organic fraction ideal for co-composting. The Solid Waste Management Rules 2026, effective April 1, mandate four-stream segregation (wet, dry, sanitary, special), boosting organic waste availability and aligning perfectly with co-composting expansion.
In urban India, where land for landfills is scarce, co-composting supports a circular economy, turning liabilities into assets amid rising fertilizer costs and soil degradation.
Case Studies from CSE Report: Lessons from the Ground
CSE examined three Indian FSTPs, revealing practical insights into implementation.
Devanahalli FSTP, Bengaluru Rural, Karnataka
Serving 33,000 residents, this 6 KLD plant mixes biosolids 1:2 with wet waste on 10 windrows across 0.25 acres. It yields 2.5-3 tonnes monthly at Rs 7/kg, generating Rs 15,000 revenue. Tests show strong nutrient profiles (N 2.09%, P 2.21%) but exceed FCO zinc limits (1660 mg/kg). Operators note low demand due to farmer skepticism, yet no odors and nil pathogens highlight viability.
Dhenkanal FSTP, Odisha
A larger 27 KLD facility for 68,000 people uses 1:4 ratio on 4 beds, producing 0.5-1 tonne/month sold at Rs 20/kg to government buyers (Rs 1.2 lakh in 2023-24). Helminth eggs (19/g) exceed USEPA Class A, but Salmonella absent. O&M costs Rs 3.1 lakh/month underscore need for subsidies.
Periyanaickenpalayam FSTP, Coimbatore, Tamil Nadu
Cluster model for five urban local bodies (ULBs), 50 KLD capacity processes 400 kg waste daily into 6 tonnes/month at Rs 3-10/kg. Benefits from field trials showing crop yield boosts, despite Salmonella spikes and low K (0.001%). Shared costs (Rs 1.4 lakh/month) make it economical.
| FSTP | Capacity (KLD) | Mix Ratio | Output (t/month) | Price (Rs/kg) | Key Issue |
|---|---|---|---|---|---|
| Devanahalli | 6 | 1:2 | 2.5-3 | 7 | Heavy metals |
| Dhenkanal | 27 | 1:4 | 0.5-1 | 20 | Pathogens |
| PNP | 50 | 1:3 | 6 | 3-10 | Low nutrients |
These pilots prove technical feasibility but flag quality inconsistencies.
Proven Benefits Driving the Co-Composting Revolution
- Nutrient Synergy: Biosolids provide NPK; organic waste adds carbon, yielding balanced fertilizer reducing chemical imports.
- Pathogen Elimination: High temperatures ensure safe reuse, meeting partial FCO/USEPA criteria.
- Environmental Gains: Cuts landfill methane (India's third-largest source), enhances soil organic matter by 20-30%.
- Economic Viability: Low capex (windrows cheap); revenue offsets 5-10% O&M in mature plants.
- Circular Economy: Aligns with SWM 2026's legacy waste remediation targets.
Field trials in Coimbatore confirm 15-20% yield increases in veggies without residue risks.
Overcoming Key Challenges
Despite promise, hurdles persist: regulatory gaps (no biosolids-specific standards), variable quality (heavy metals from urban sludge), farmer reluctance (perceived contamination), and logistics (sourcing consistent organic waste). Economics show losses (Rs 2-3 lakh/month O&M vs low sales), demanding subsidies. CSE urges national guidelines and training.
Regulatory Framework and CSE's Policy Roadmap
India's National Faecal Sludge Policy 2017 and SWM Rules 2016 encourage reuse but lack biosolids specifics; FCO 2023 guides compost quality. CSE recommends: unified standards, government procurement mandates, farmer demos, and SBM 2.0 integration for 100% FSTP reuse by 2030. For details, explore the full CSE report.
New SWM Rules 2026 enforce segregation, aiding supply chains.
Stakeholder Perspectives and Future Outlook
ULB operators praise scalability for small towns; farmers seek certification for trust. With MSW organic fraction at 50%, potential output could hit millions of tonnes yearly, slashing fertilizer bills (Rs 2.5 lakh crore imports). By 2030, co-composting could treat 80% biosolids, supporting Viksit Bharat's net-zero goals. Innovations like rotary drums promise efficiency gains.
Actionable Steps for Scaling Co-Composting Nationwide
- ULBs: Invest in segregation, partner FSM agencies.
- Farmers: Trial certified co-compost for soil tests.
- Policymakers: Enforce FCO, subsidize pilots.
- Researchers: Monitor long-term soil impacts.
India's co-composting revolution, catalyzed by CSE's insights, promises resilient waste-to-resource systems.
Photo by Amaan Abid on Unsplash