Wednesday, July 17, 2024

Landfill Mining

Bronwyn Slater asks if the emerging technology of landfill mining could eventually result in the elimination of all existing landfills.

Millions of landfills exist all over the world and many have now been covered over and closed as incineration becomes the preferred option for waste disposal in many jurisdictions.  Most or all of the rubbish buried in landfill still exists, because very little breaks down in a sealed oxygen-deprived environment.  Landfill mining, a relatively new technology which involves digging up old landfills and in many cases completely emptying them, may eventually eradicate landfills from the face of the earth.

It’s worth pointing out that humans have always had to deal with garbage, and they have done so in various ways including burning, burying and dumping it in rivers or even in the streets.  The first recorded landfill in history is located in Knossos, Crete where large holes were dug into the earth to dump refuse.  On the banks of the Tiber, the Monte Testaccio, also known as the third hill of Rome, is an artificial mound built almost entirely of fragments of broken amphorae (clay bottles) dating back to the time of the Roman Empire.

Broken clay bottles (amphorae) on an ancient Roman dumping ground

In the Middle Ages people dumped waste in streets, ditches and public waterways.  In 15th century Paris huge piles of garbage were dumped outside the city’s walls.  In many other European cities it was common for residents to dispose of rotting food and other trash by tossing it out the window – it was widely believed that wild dogs would consume the refuse.

Prior to the introduction of municipal waste disposal systems individuals burned or buried their waste.  Before the Industrial Revolution most of this waste was organic and would have broken down naturally.  And today, for anyone lucky enough to stumble upon any surviving relics of the past, they could be worth a fortune.

But today the story is very different.  For more than 100 years, the world has been discarding its unwanted waste in landfill sites. There are at least half a million of these sites in Europe alone.  Most have now closed, in line with the EU’s Landfill Directive, as Europe moves to waste incineration and increased recycling.

Landfills are not designed to break down waste, only to store it.  In an oxygen-free environment trash does decompose, albeit very slowly.  So there are millions of these sealed sarcophagi all around the world containing massive amounts of tightly compacted garbage which will remain unchanged for no-one knows how long. 

How Landfills Work

Waste is dumped into a specific area (called a ‘cell’) of the landfill and is then compacted by a tractor with spiked wheels that goes back and forth over the garbage.  The compactor makes three to five passes over the garbage to crush as much into the space as possible.  On average, about 1,200 to 1,400 pounds of waste can be compacted into one cubic yard of space.  At the end of each day, the working face of the cell is covered with a layer of soil or other cover material to minimize odour, pests and rodents as well as litter.  This three-step process is repeated over and over until the cell is filled.

Landfill sizes vary.  The largest in the world range in size from 200 to 2000 acres in surface area. 

Modern vs. Older Landfills

Modern landfills in most developed countries are classed as ‘sanitary’ landfills.  This means they are thoroughly insulated so that toxins do not leach into the groundwater, and methane is collected rather than allowed to escape into the atmosphere.

They are sealed with impermeable synthetic bottom liners which include 2 feet of clay, a plastic liner and a protective layer 2 feet thick, usually comprised of sand.

A storm water drainage system collects rainwater that falls on the landfill and a leachate collection system collects liquids and any rainwater that comes into contact with the garbage.

The average life expectancy of a landfill could be anywhere from 30 to 50 years.  When the landfill is completed, it is capped with a layer of clay or a synthetic liner in order to prevent water from entering.  Landfills must be monitored for 30 years after closure.

However, 90% of European landfills pre-date the 1999 Landfill Directive and are classed as “non-sanitary”.  They have little or no protection or liner technologies and many are simply “waste dumps”.  They often leak their unprocessed leachate into the groundwater, and so present a danger to public health.  They are also a major source of methane emissions.

Landfill Mining

Landfill mining is the process of excavating waste from landfills in order to reduce their environmental impact.  Waste is excavated and then separated into its constituent parts such as glass, metal, plastic, soil and other material that can be then used as fuel to generate electricity.  The glass, metal and plastic is recycled.

Landfills, especially older landfills which were in use prior to the introduction of recycling, contain large amounts of valuable metals.  Aluminium, copper, zinc and steel are high value commodities, and are recoverable from tin cans, scrap metal, electronic devices and other objects.  The concentration of aluminium in landfills can often be higher than the concentration of aluminum in bauxite from which the virgin metal is derived.

Landfills are now starting to be viewed as an untapped resource for many of these strategic metals.  In the UK alone, 2 billion tons of waste sit untouched in landfills.  In the US, more than 4.6 million tons of electronic waste were disposed of in landfills in the year 2000 alone.

While the cost of landfill mining is extremely high, it can be offset by the revenue generated by recycling and the production of energy from the fuel fraction contained in the landfill.  Other important benefits may include avoided liability through site remediation, reductions in closure costs, and reclamation of land for other uses.

The concept of mining landfills is not new.  Some 60 examples have been cited in solid waste literature since the first reported project in Israel in the 1950s.  The EU has been conducting research on the feasibility of landfill mining via ETN NEW-MINE (for municipal solid waste) and METGROW+ (for industrial waste).  The following video describes the approach of ‘New-Mine’:

In his report ‘Landfill Mining – Process, Feasibility, Economy, Benefit and Limitations’, Rosendal states that “many landfill mining projects have been carried out throughout the world during the last 50 years, but it is very difficult to find good reliable data.  In general, a mining project involves a significant financial investment and is not free of risks.”

However, analysts predict that the technology will improve into the future, making landfill mining more economically viable for companies looking to make a profit.  Another factor which will accelerate the technology is the need for more landfill space, as many cities around the world are running out of space and have begun to excavate existing landfills in order to create more.

At this point in time landfill mining will primarily be motivated by profit and public health and safety concerns, but it is not beyond the realms of possibility that at some point in the future technology will have reached a point where all landfills can be successfully be mined and thereby eliminated altogether.

For those who, like myself, hate waste and feel extremely uncomfortable with the idea of landfills, this new technology is cause for optimism.


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