Wastepickers run biogas plants in Mumbai, India

By Virali Gokaldas and the Global Alliance for Incinerator Alternatives

Mumbai’s rapid growth, high density, and sheer size present significant challenges for its waste management system. The enormous quantity of waste generated in the city makes large-scale, technologically driven “solutions” tempting. However, the opposite approach—a highly decentralized, people-powered model of waste management—has proven successful. Dry waste is separated out for recycling while organic waste, Mumbai’s largest and heaviest waste stream, is treated close to its source through composting pits and biogas. This approach has reduced the need for costly transportation and landfill space while providing green jobs for waste pickers.

Parisar Bhaginis in their uniforms. (photo: Michael Atkin).

The Indian Municipal Solid Waste Rules of 2000 require source separation of waste and prohibit landfilling of biodegradable waste, but there is no formal recycling or composting program in Mumbai. There is, however, a thriving informal recycling economy. A large percentage of dry recyclables—meaning paper, plastic, metals, and glass—are recycled by waste pickers. This recycling sector is considered to be ‘informal’ since it is not regulated by government agencies, and there are no rules for pricing recyclable materials or protections for the health and safety of the waste pickers.

Because poor, low-caste women comprise 85 percent of the waste picker population, Stree Mukti Sanghatana (SMS), a non-governmental organization, started the Parisar Vikas (PV) program to train informal recyclers as “parisar bhaginis,” or “neighborhood sisters.” The bhaginis are taught the principles of zero waste, how to sort and handle waste from multi-family dwellings, composting and biogas plant management, gardening, and how to organize as worker cooperatives and negotiate contracts.

Through SMS programs, a total of 600 women work in almost 150 locations in Mumbai, ranging from institutional campuses to housing apartments. They bundle the dry, recyclable waste for sale to industry recyclers. Residuals and organics are either picked up by the city for disposal at dumpsites, or by SMS to be processed in composting and biogas facilities that produce manure and biogas for industry and domestic end uses.

Bhaginis earn income from the sale of recyclables and sometimes also receive a service fee for collecting, sorting, or managing composting pits/biogas plants. Most earn US $2 – $3 per day from collection fees and sale of recyclables, though this can vary considerably. Some apartments pay the waste pickers directly; others pay the co-op.

The cooperatives enter into recycling contracts with institutions, apartment complexes, businesses, and the municipality. They have seen the greatest success with private institutions and campuses, such as the Tata Institute for Social Sciences. At the institute, a cooperative operates a snack bar, sorting operation, and biogas facility. The snack bar generates 25 – 30 kg of clean, source-separated, organic waste per day. Supplemented with outside sources, this feeds the 100 kg/day capacity biogas plant. Gas from the plant meets a quarter of the canteen’s cooking gas needs. The operation has been so successful that the institute added another 500 kg/day plant at its larger canteen, and is constructing a third plant to service their new 1,000-student hostel.

Current contracts between the collector (SMS or the cooperative) and their customers are short, basic letters of agreement that allow bhaginis to come on-site to take dry recyclables away or to manage an operation for a set fee. The letters are typically signed and renewed on an annual basis and detail the number of bhaginis to be on site and the fee to be paid. Additional provisions include the necessity of safety and protection equipment, the need for identity cards to allow ease of access, and a requirement for worked hours to be documented.


A key innovation in PV’s model is the adoption of a locally viable technology for biogas creation, called the Nisargruna Biogas Plant. The technology was developed to convert on-site organic waste at an individual institution or apartment building into useful methane and high-quality manure (fertilizer) to then be sold back to households or local businesses. It was designed to digest almost any biodegradable waste including kitchen waste, paper, animal dung, bio-sludge, poultry manure, agro-waste, and biomass.

The Nisargruna Biogas technology has three stages of operation. First, waste must be properly separated before entering the biogas plant as some materials may damage the equipment. Even with good source separation, waste pickers conduct a sort on-site to pick out contaminants and inappropriate organic material. Hence waste pickers are a critical part of the operation’s smooth functioning. Second, because microorganisms cannot easily digest solid waste, the waste is placed in a mixer with an equal amount of hot water to break down fibers and create a homogeneous slurry. This slurry enters into the aerobic tank to be converted to butyric, fumaric, acetic, and other organic acids. Finally, the acidic slurry transfers to the anaerobic tank, to be converted into methane. The final products are nitrogen-rich manure, to be used on gardens, and methane gas, which can be used for heating or electricity. The water used in the process is heated through solar power and recycled for new batches. Out of every 100 liters of water used, 75 liters are recycled from the slurry.

Plant operation is relatively simple as the technology was designed to be used by non-skilled workers. And, unlike composting operations, a biogas plant does not create unpleasant decomposing odors, nor does it take up a large amount of space. Only 50 m2 are required for a plant that processes 100 kg per day. The resulting biogas is 85 percent methane, more efficient than the 50 percent methane typical of most biogas plants, which SMS attributes to Nisargruna’s two-step aerobic/anaerobic process. The small footprint, lack of odors, and direct use of biogas for heating mean that organic waste, the largest part of the waste stream, can be processed and used very close to where it is produced. This dramatically reduces the need for waste pick up, transport, and disposal, as well as the pollution associated with these activities. It also avoids the pollution that results from landfilling wet waste: methane emissions, toxic leachate, and odors.

The municipality saves considerable money in avoided transport and disposal costs. The city pays private contractors about US $11 per ton to transport the waste and another US $9 for disposal. So each one ton/day plant saves the city in excess of US $6,000 per year. These costs are not reimbursed to PV.

For a biogas plant handling five metric tons per day of wet waste, the environmental benefits are significant. On an annual basis, the plant saves greenhouse gas emissions equivalent to 4,197 tons of CO2 from recycling wet waste. The same plant creates, annually, biogas equivalent to 55,000 kg of liquefied petroleum gas and 10,000 kg of organic compost. This is in addition to the reduced impact of transportation on Mumbai’s crowded streets.

SMS has successfully demonstrated the viability of decentralized waste management in one of the world’s largest and most crowded cities. Although this approach takes more time to roll out than a one size-fits-all city-wide strategy, its greater flexibility and customization is important to its success. Waste picker cooperatives are instrumental in managing source separation, and the small-scale biogas and compost pits have generated higher-paying employment for women waste pickers while significantly reducing the waste burden on the municipality.

Copyleft GAIA. You may reprint this article in whole or in part.  Please credit any text or original research you use to Global Alliance for Incinerator Alternatives, On the Road to Zero Waste: Successes and Lessons from Around the World.