From dumpsite to construction site: Can geopolymer technology solve India’s legacy waste crisis?

India faces a mounting challenge as the September 2026 deadline for the Swachh Bharat Mission-Urban (SBM) 2.0 approaches. According to the SBM dashboard, more than 88.20 million tonnes of legacy waste still need to be managed, with states such as Maharashtra (29.6 million tonnes), Rajasthan (8.5 million tonnes) and Karnataka (10.6 million tonnes) accounting for a large share.

While cities including Delhi have expanded biomining capacity to process up to 30,000 metric tonnes a day, a key question remains: What should be done with the processed “fine fraction waste” (FFW)?

A recent study offers a potential answer. Published in the peer-reviewed Journal of Process Safety and Environmental Protection, it suggests geopolymer technology can safely lock in hazardous heavy metals from FFW and convert it into a usable, green construction material.

The “fine” problem with legacy waste

Excavating old landfills produces more than plastics or combustible materials. A significant share — typically 40 per cent to 80 per cent of the total mass — is a fine soil-like fraction, usually smaller than 4mm. Though it resembles soil, it is often heavily contaminated.

A study by IIT Bombay, analysing FFW from Ahmedabad’s landfill, found elevated levels of heavy metals, including chromium and lead, averaging 166 milligrams per kilogram (mg/kg) and 105.19 mg/kg respectively. These exceed India’s compost standards by 232 per cent for chromium and 5 per cent for lead.

Such contamination makes FFW unsuitable for direct use as compost or even simple landfill cover. Reburying it, experts say, defeats the purpose of landfill mining.

A dual approach: stabilising and reusing

The study presents an innovative approach to hazardous waste stabilisation, replacing conventional cement-based methods with geopolymer technology to produce more environmentally safe construction materials. Conventional cement production accounts for nearly 8 per cent of global carbon dioxide (CO₂) emissions. By contrast, this alternative uses a binder derived from industrial by-products.

The process involves mixing contaminated waste with a geopolymer binder made from fly ash — a by-product of thermal power plants — and an alkaline solution. This triggers a chemical reaction that forms a dense, three-dimensional structure, effectively trapping heavy metals and preventing them from leaching into the environment.

The resulting construction blocks show promising results:

• Structural strength: Blocks with 25 per cent contaminated waste achieve compressive strength of up to 33 megapascal (MPa), suitable for paving, landscaping and landfill cover

• Environmental safety: Leaching tests show chromium at 1.53mg/L and lead at 1.87mg/L — both within regulatory safety limits

• Durability: The material withstands temperatures up to 550 degrees Celsius (°C) and survives freeze-thaw cycles, suggesting resilience across varied climates

Careful assessment remains essential, says Richa Singh, research scientist at University College Dublin and lead author of the paper. “Fine fraction waste often contains hazardous chemicals, making chemical characterisation extremely important before any reuse,” she says.

“Using FFW in a geopolymeric matrix minimizes the leaching potential of these contaminants, effectively turning a hazardous material into a safe, usable construction product, a true win-win scenario. Scaling this approach, however, will require close collaboration between urban local bodies, waste management contractors, and research institutions to ensure region-specific mix designs, rigorous testing, and effective implementation,” she added.         

A solution for cities under pressure

With the 2026 deadline approaching, cities face increasing pressure to clear landfill sites. Managing the recovered waste — including refuse-derived fuel (RDF) and FFW — remains a major challenge.

Currently, some contractors use FFW as filler in low-lying areas, while recent guidelines suggest its use in road construction. However, these approaches may not be suitable everywhere, which will need innovative, scalable, and evidence-based solutions. 

Meanwhile, the Bombay High Court has called for urgent technological measures to tackle pollution at Mumbai’s Kanjurmarg dumpsite.

Geopolymer technology could offer an alternative. By converting toxic FFW into construction material, it provides a potentially safer and more economically viable route for managing the estimated 16.8 million tonnes of waste still awaiting remediation. By combining two waste streams, FFW and fly ash, the approach also supports a circular economy, reduces reliance on virgin sand and lowers the carbon footprint of construction.

Promise and limits of geopolymers

Geopolymers have long been studied as an alternative to cement for stabilising contaminated waste, both in India and internationally. While results are encouraging, challenges remain. Higher proportions of FFW (above 40 per cent) can reduce mechanical strength and increase the risk of leaching. This means mix designs must be tailored to the specific composition of waste, which varies across regions.

For instance, data from Tamil Nadu’s Perungudi dumpsite, where 94 acres are being reclaimed, shows significant variation in both the quantity and quality of FFW. This underlines the need for careful testing and monitoring before scaling up.

With the Union Ministry of Housing and Urban Affairs launching the Dumpsite Remediation Acceleration Programme, which offers Rs 550 per tonne of waste, investment in such technologies could prove significant.

Rather than simply clearing waste, the focus could shift towards reuse. For millions living near landfill sites in cities such as Delhi, Mumbai and Chennai, the approach offers more than a technical fix. It suggests a pathway towards cleaner, healthier and more sustainable urban environments.