Aafrin Kidwai 
Picture credit: by Ropable, https://commons.wikimedia.org/w/index.php?curid=530271
- What is legacy waste?
Legacy waste typically refers to aged municipal solid waste in landfills or dumpsites. In India, there is no agreement on the minimum age of waste to be considered legacy waste and there is no formal definition of legacy waste. The term “legacy waste clearance” has become synonymous with the removal of poorly planned and managed dumpsites that may be posing long-term risks to the environment and public health.
2. What is legacy waste composed of?
Typically, fresh municipal solid waste and legacy waste are mixed together at dump sites in India. This includes biodegradable waste that has partially or completely decomposed, plastic waste, textiles, metals, glass, and other materials. Legacy waste differs from new municipal solid waste in terms of composition and characteristics. The selection of treatment technologies and the final use of recovered materials are both significantly influenced by this difference. Fines are typically the single largest element of legacy waste.
3. Does the composition of legacy waste differ across locations?
Yes. The region and age of a dumpsite affect the legacy waste’s composition. For instance, the fine percentage in Hyderabad and Delhi is almost 75%, indicating that the dumpsites are old and the organic waste has been deteriorating for many years. However, because the dumpsites in Ahmedabad and Mumbai are more recent, the proportion of fines is relatively lower. The activities of the informal sector involved in recycling extraction determine the amount of recyclables.
4. How is legacy waste treated?
The two methods for remediating dump sites are biocapping and biomining. In order to reduce the amount of rainwater seeping into the legacy waste below, a high-density polyethylene (HDPE) liner, a clay liner, and a vegetative cover are used in the scientific process known as biocapping. Leachate and landfill gas collection and treatment systems have been installed. However, it is not practically possible to recover all landfill gases and leachate from a non-scientific landfill. Although capping might seem like a quick and easy way to remediate a dumpsite, it does not reclaim the land or ensure that legacy waste is treated scientifically. Thus, it leaves behind lingering risks to human health and the environment. Due to these factors, urban local government entities must choose biomining over biocapping, according to the Solid Waste Management Rules of 2016 and several National Green Tribunal (NGT) directives.
5. What is India’s experience in biomining?
The Deonar dumpsite in Mumbai was mined in 1989 as a pilot case study for using compostable waste. At the Kodungaiyur and Perungudi dumpsites in Chennai, Kurian Joseph and his research team from Anna University pioneered the study of legacy waste in 2003.
6. Is there a business case for legacy waste clearance through biomining?
Yes. When historical waste dumps are the subject of scientific mining operations, a sustainable business model is produced. Three main goals may be attained by mining dump sites:
- Increase landfill capacity or allow other uses for the land beneath the dumpsite
- Yield scrap combustible fraction (SCF) from scrap polymeric and combustible materials
- A yield inert fraction that can be applied to geotechnical and construction projects.
7. What do the SWM Rules (2016) say about biomining?
The responsibilities of local governments, village panchayats, census towns, and urban agglomerations for remediating dumpsites are outlined in Rule 15. All open dumpsites and currently operating dumpsites must be examined for their potential for biomining and bioremediation, and, if practical, the necessary steps must be taken to biomine or bioremediate the sites. The Rules state that if a dumpsite cannot be used for biomining or bioremediation, it must be scientifically capped in accordance with landfill capping standards to stop further environmental harm.
8. What are some of the steps involved in biomining of legacy waste?
Dumpsite remediation through biomining has six broad steps, including:
- A pre-feasibility assessment that includes extensive site investigation studies, surveys, and waste characterization
- Systematic removal of legacy waste
- Stabilization by bioculture spraying to reduce waste volume and mass
- Processing of the excavated fraction
- Use of extracted waste fractions in various profitable applications; and
- Clearing and preparing recovered land.
