Kolkata attempts to eliminate ‘legacy waste’ in landfills through biomining

Kolkata attempts to eliminate ‘legacy waste’ in landfills through biomining

Subject :Environment

Section: Pollution

Context:

• The Dhapa landfill, Kolkata’s main municipal dumping ground since 1987, has been causing frequent fires and subsequent air quality deterioration in the city.

Details:

• Dhapa has been undergoing biomining and bioremediation, the methods chosen by the National Green Tribunal for clearing legacy waste, which allows the extraction of usable materials from the waste.
• Though the project began in 2019, as of February this year, 0.78 million tonnes of the 4 million tonnes of legacy waste has been processed, with the COVID-19 pandemic landing a blow to the progress.

Dhapa landfill:

• The Dhapa land was originally part of the East Kolkata Wetlands, which serves as Kolkata’s natural sewage treatment system and was designated a Ramsar site in 2002, as a wetland of global importance.
• Dhapa is spread over 35 hectares – a little over half the size of Eden Gardens cricket ground. Of this area, 12 hectares have been closed, capped and covered with grass after covering the waste with a geotextile membrane, with support from a World Bank project.
• Another 23 hectares are currently active, with new waste coming in while legacy waste is still being processed.

Harmful environmental impact of landfills:

• Landfills are known to greatly contribute to global warming, as they produce methane, a greenhouse gas that possesses a global warming potential over 21 times that of carbon dioxide.
• Municipal solid waste landfills are considered the third-largest source of methane generated from human activities.
  • Methane facilitates fires, which worsen air quality.
• Leachate in landfills leads to pollution of groundwater, surface water, soil and air. It also contaminate the drinking water with heavy metals.

Legacy wastes:

• Legacy wastes are the wastes that have been collected and kept for years at some barren land or a place dedicated to Landfill (an area to dump solid waste).
• This waste can be roughly grouped into four categories:
  • Contained and/or stored waste(contained or stored waste are wastes in tanks, canisters, and stainless steel bins).
  • Buried waste.
  • Contaminated soil and groundwater
  • Contaminated building materials and structures.
• The biomining method has been proposed by the Central Pollution Control Board (CPCB) for the effective disposal of legacy wastes.
• The CPCB, in 2019, estimated that “more than 10,000 hectares of urban land is locked” in the form of ‘legacy wastes’ in landfills across the country.
• Environmental Impact of Legacy Waste:
• Legacy wastes not only occupy large spaces but also become a breeding ground for pathogens, flies, malodours and the generation of leachate (a liquid generated by airless waste that pollutes soil and groundwater).
• They also contribute to the generation of greenhouse gases and pose a risk of an uncontrollable fire.

Biomining:

• According to the Central Pollution Control Board (CPCB) guidelines, “Biomining is the scientific process of excavation, treatment, segregation and gainful utilisation of aged municipal solid waste lying in dumpsites typically referred to as legacy waste.”
• In this process, microorganisms (microbes) are used to extract metals of economic interest from rock ores or mine waste.
• It comprises 4 steps:
  • excavation of legacy waste,
  • stabilising the waste using bioremediation,
  • segregation of excavated waste and
  • sustainable management and its safe disposal.
• The methods of biomining include Bioleaching, Bio-oxidation, Dump leaching, and Agitated leaching.
• It is usually used for old dumped waste that remains in a partly or fully decomposed state with no segregation in existence between wet and dry waste.
• In the cost-effective method of biomining, treatment is done by dividing the garbage heap at the site into suitable blocks to let the air percolate in the heap.
• As a result, the leachate which is the water in the heap with suspended solid particles is drained off and microbes are sprayed in the heap to initiate biological decompositions.
• The waste is turned over several times in order to devoid the waste from leachate as much as possible.
• This biological decomposition of the waste decreases the volume of the waste by 40%.