Plazoo

Drive out of almost any Indian city and you will pass it sooner or later. A grey hill by the highway, with smoke rising from one corner, birds circling overhead and a smell that reaches you before the sight does.

That hill is a dumpsite, and most of what sits in it was thrown there 10, 20 or even 30 years ago. Cities kept adding to it because there was nowhere else to send the garbage.

That old, accumulated waste is called legacy waste. This article explains what it is, why it matters, and how cities are now digging it out and clearing the land.

What legacy waste is

Legacy waste is municipal solid waste that has been dumped and left untreated at a site for years. It was never segregated, never processed, and never covered properly.

Over time, the organic part of it breaks down. What is left is a packed mix of soil-like material, plastic bags and wrappers, cloth, rubber, glass, stones, construction debris and bits of metal.

Under the Swachh Bharat Mission (Urban) 2.0, cities across India have been asked to clear their old dumpsites. That is why legacy waste projects are now running in big metros as well as smaller towns.

Why old dumpsites are a problem

• Fires: decomposing waste gives off methane, which catches fire easily. Dumpsite fires can smoulder for days and fill nearby areas with toxic smoke.


• Groundwater pollution: rainwater seeps through the waste and picks up chemicals and heavy metals. This dark liquid, called leachate, reaches wells and borewells around the site.


• Greenhouse gases: methane traps far more heat than carbon dioxide, so large dumpsites add to climate change year after year.


• Health of nearby residents: families living close to dumpsites deal with flies, mosquitoes, bad air and contaminated water every day.


• Locked land: acres of land near the city sit unusable. In a growing city, that land could hold a park, a waste processing plant or public facilities.

And the longer a dumpsite stays, the higher and harder to handle it gets.

How biomining works

The most common way to clear legacy waste in India is biomining. In simple words, the old waste is dug out, treated, sieved and sorted, and each part is sent where it can be used or safely disposed of.

1. Site survey: the team measures how much waste is there, how deep it goes and what it is made of. This decides the machines and the timeline.


2. Bioremediation: the waste is spread out in rows and sprayed with microbial cultures. It is turned regularly so air gets in. Over a few weeks, the remaining organic matter breaks down, moisture drops and the smell reduces.


3. Excavation: excavators and loaders dig out the waste layer by layer and feed it to the processing line.


4. Screening: trommel screens, which are large rotating drums with holes, sieve the material by size. Fine soil-like material falls through, and larger pieces move ahead.


5. Separation: further screens, air separators and magnets pull out plastics, cloth, stones, debris and metal into separate streams.


6. Dispatch: each stream is stacked and sent to its buyer or disposal point.

Once the waste is cleared, the land is levelled and can be handed back to the city for new use.

Where each separated part goes

When screening and separation are done well, only a small share of the original waste should need to go to a landfill.

What to plan for before starting a biomining project

• Know the waste: a proper survey with sampling at different depths tells you how much soil, plastic and debris to expect. Machines chosen without this often get choked or run below capacity.


• Match machine capacity to the deadline: work out the tonnes per day needed to finish on time, and pick screens and conveyors that can actually handle it.


• Plan for monsoon: wet waste is heavy and sticky and screens poorly. Build the rainy months into the schedule.


• Line up buyers early: fix arrangements with cement plants for RDF and with contractors for soil and inerts before processing starts. Otherwise sorted material piles up on site.


• Handle leachate and dust: collect leachate, spray water to control dust, and keep fire safety equipment on site through the project.


• Maintenance: screens, belts and motors run in harsh conditions. Spare parts and service support close to the site save days of downtime.

Clearing the hill for good

Every old dumpsite cleared means cleaner air and water for the people living around it, and land the city can use again. The work is slow and heavy, but the method is proven and the results are visible.

Arcler Projects LLP, based in Ahmedabad, designs and supplies processing equipment for legacy waste and biomining projects, including screening and separation systems. If you are planning a dumpsite clearance project, you can see how their setups work at Arcler Projects.