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There's gold in them there landfills

Ed DouglasNew Scientist

01 October 2008 - IN THE movie WALL_E, humankind has left Earth in a bit of a mess. The planet is choked with garbage and all the people have shipped out, leaving robot WALL_E to clean the place up and make it habitable again. Things may not be quite that bad yet, but there's no doubt that we produce a huge amount of waste. Even with increased recycling, landfill sites are filling up by the day and -in the absence of a plucky robot - the waste experts of planet Earth are working on the next best thing: landfill mining.

The idea is simple. Instead of disappearing under mountains of our own waste, while paying through the nose for diminishing commodities, why not dig up and recycle what we have already thrown away?

Next week, industry experts will gather in London for the first global landfill mining conference. Bringing together environmental scientists, economists and landfill operators, the one-day meeting promises to show delegates how to turn waste into "garbage gold".

Landfill mining has been tried before. The first scheme began in 1953 at Hiriya garbage dump outside Tel Aviv, Israel, and aimed to reclaim fine-particle waste rich in minerals to improve soil quality at local citrus fruit farms. The landfill closed in 1998, but the recycling plant that remains on the site still produces soil improver from green waste. Then during the 1960s and 1970s, a handful of sites in the US began separating waste to recycle the steel and to compost food scraps. In the late 1980s, a pilot programme was set up to extract recyclables from a small, community landfill in the town of Edinburg, New York, and burn the solid residue to generate energy. This pilot proved uneconomical but during the oil price spike of the 1990s interest in the economic value of waste soared. Investors clamoured to snap up scrap metal companies, only for the price of commodities to drop through the floor in the mid-1990s.

Yet now that commodities prices are rising once more, environmental issues are high on everyone's list of priorities and land prices are increasing, every square kilometre is worth too much to use for landfill. Raiding the dump seems like a good idea again. This time the prospects are more promising. Thanks to a decade of innovation by the recycling industry, the technology to process landfill waste is more readily available.

So what's in a landfill worth recycling? For a start, the average landfill is strewn with valuable - and sometimes even precious - metals. Aluminium, from drinks cans, is just one example. According to Patrick Atkins, environmental consultant for private equity fund Pegasus Capital Advisors, and until recently director of energy innovation at US aluminium producer Alcoa, Americans throw away 317 aluminium cans every second of every day. Around half of these, totalling 680,000 tonnes of aluminium each year, dodge the recycling bin and end up in landfill. Given that the cost of aluminium peaked at $2700 per tonne in July this means America is burying up to $1.83 billion worth of metal per year. Atkins estimates that there is now more aluminium in US landfills than can be produced from ores globally in one year. And it's not only aluminium that is lurking down there with the used diapers and grocery bags. One tonne of scrap from discarded PCs contains more gold than can be produced from 16 tonnes of ore, he says. And the world throws away 18 million tonnes of electronic waste each year.

Nowadays it is relatively easy to separate the metal you want from the junk you don't using recycling technologies. Eddy current magnets, for example, can deflect aluminium and other non-ferrous metals from a flowing stream of waste. Plastic, too, is becoming easier to pick out. Rather than the more expensive process of doing it by hand, some plastic sorting plants are now using spectroscopic scanners, which sort different types based on the spectrum of light they absorb. And since rising prices are making oil seem like an expensive raw material to produce plastics, recycling existing plastic from landfill seems sensible.

Metals and plastics are only part of it, says William Hogland, an environmental engineer at the University of Kalmar in Sweden. All that smelly food and other organic waste rots down sooner or later. And as the TelAviv project discovered back in the 1950s, even this can be worth digging up.

"The earth fraction of landfill can be one of the most profitable as coverage material, compost and for lawn improvement," Hogland says. There's also plenty of combustible material in landfills. One kilogram of the coarse earth fraction - containing particles greater than 50 millimetres across - yields between 6 and 10 megajoules of energy, Hogland says, and the average Swedish landfill has 40 million tonnes of the stuff. Burning that waste is a controversial idea because of toxins that may be released in the process. But, Hogland says, thanks to new technology for cleaning flue gases, Sweden is building new incinerators to provide heat and light for local communities. Too good to waste

So if landfill sites are, sometimes literally, gold mines, why aren't companies tearing into them already? For its part, Alcoa has invested heavily in stopping as many cans as it can from reaching a landfill, but has stopped short of digging them up again. "It's not something we are doing at this point," said Alcoa spokesman Kevin Lowery. "If we thought it was the most efficient thing, we'd do it."

Part of the reason for this reticence is that while aluminium can be recycled at a fraction of the cost of producing it from ore, and using 94 per cent less energy, that's only the case once you have collected the cans. Getting them out of landfill is more expensive than buying aluminium directly from a recycling plant. Plus no two landfill sites are the same. Each has a different blend of useful materials, mixed with all kinds of less useful or dangerous materials such as asbestos. And when you consider that companies would likely want to mine more than one site, covered perhaps by different state or national regulations, it starts to look like too much trouble.

Reid Lifset, an industrial ecologist at Yale University who has investigated the prospect of extracting copper from landfills, has come to a similar conclusion. "With current technology and prices, landfill mining is generally not economically viable," he says. "The benefits such as revenue from sale of recovered metals, [and] reduction in regulatory costs, generally did not outweigh the costs." In other words, there may be a lot of copper buried in landfills, but if copper is your thing, a huge mine with gigantic equipment makes more sense than picking your way through several different landfill sites.

Advocates of landfill mining argue that with more imagination and a sober assessment of the true cost of burying trash, there is a viable economic case for landfill mining. He and his colleagues have calculated that reclaiming sites in the Baltic region alone could generate billions of euros from various revenue streams. Rather than approaching landfill mining with one outcome in mind, Hogland says, you have to look at the overall advantages, including environmental services like protecting water quality.

In the European Union, for example, landfill regulations mean that operators are responsible for controlling and monitoring pollution from the run-off. That cost stays with the company for decades. There are countless older landfill sites in the EU that Hogland says are in need of remediation. Companies with old landfills on their property need plans for their aftercare. Mining them could offer them that. Landfills also produce huge amounts of gases, particularly methane, which is 21 times as potent a greenhouse as carbon dioxide. Shutting off this source would clearly be a good thing.

This is even more important in the vast open dumps that disfigure the megacities of Asia and Africa. Few of these have any control over the release of methane, and most are also unlined, allowing toxic liquid to run into watercourses. Environmental engineer Kurian Joseph at Anna University in Chennai, India, suggests that one way to improve matters would be to industrially compost organic matter and recycle what is left. That will take huge investment, but Hogland suggests western companies could earn carbon credits by mining landfills in the developing world to prevent the release of methane and carbon dioxide. He knows of at least one company that is looking into it.

In the EU and North America, however, methane is already collected and burned as biogas. Waste consultant Peter Jones warns that operators in the UK will not mine landfills until they have stopped producing this valuable gas. Under renewable energy incentives, he says, UK operators get £1 million for every megawatt of generating capacity they install that uses methane as its fuel, so they will not jeopardise that source while it lasts. "Anyway, [mining] would never be allowed on grounds of uncontrolled methane releases and safety."

However, Joeri Jacobs of Dutch waste company Afvalzorg, says that landfills can be mined sooner if you accelerate methane production. The liquid that collects at the bottom of the landfill can be reintroduced into the top through infiltration ponds or drainage pipes. This feeds the organic matter that is already producing methane and can even start the process in "quieter" parts of the landfill. The same amount of gas is produced as through normal "biodigestion", it is simply produced more quickly.

Ultimately, though, the impetus to mine landfill sites may come not just from the value of their contents, nor from environmental savings, but from the value of the land they were built on. Reclaiming landfill sites for construction has already proved profitable in the city of Sharjah in the Persian Gulf. There, Singapore-based waste-management company IUT has successfully reclaimed the city's 190-hectare dump to build housing, a shopping centre, a hospital and a highway.

They did this by first flushing the landfill site with oxygen to kill off the anaerobic bacteria that produce the methane. Then they stripped off layers of trash, 3 metres at a time, and fed them into a sequence of conveyors, filters, magnets and shredders which separated the waste by material type, size and weight. Plastics, iron-containing metals, wood, and rocks were collected for re-use, recycling or to be turned into "refuse-derived fuel", while inert waste like rocks and sand was moved to the city's new landfill site, out of town.

Using this method, IUT says it is possible to reduce the volume of waste in a landfill by up to 60 per cent. In the west, where there is ferocious public opposition to new landfills, this could have real advantages by helping to keep existing ones open for longer. No one wants to live next to a new landfill (forget "nimby", the modern acronym is "banana" - build absolutely nothing anywhere near anything). And if we're all going to get our way, we either need a plucky robot to clean up after us, or someone needs to roll up their sleeves and start raking through the trash. Ed Douglas is a freelance writer based in Sheffield, UK

From issue 2676 of New Scientist magazine, 01 October 2008, page 34-36


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