Mining old garbage dumps

Posted on August 16, 2011. Filed under: Waste |

-The Star-

LANDFILLS are said to be the next gold mine. Prospectors are keen to mine old garbage dumps for valuable recyclables such as metals, plastics and rubber. These had ended up in dumps as waste separation and recycling were not the norm in the past, plus there was no recycling technology for some wastes back then.

In landfill mining, old rubbish heaps are dug up and recyclables are retrieved. Depending on the type of technology used, the remaining waste can be processed to tap energy or composted.

Several proposals on landfill mining have reached the Department of National Solid Waste Management but it has not approved any as the companies had not submitted the detailed studies required.

“We want the full study as they must convince us that it is safe and worthwhile to dig out the waste,” says director-general Datuk Dr Nadzri Yahaya. “In one proposal (for a landfill in Kuala Lumpur), the waste is 200m high and 300m deep. What will be the cost of digging out and disposing of that huge volume of waste? How will they do it? And where are they going to send the (excavated) waste? As the owner of Bukit Tagar landfill, we can refuse to accept the (excavated) waste as it will shorten the lifespan of the landfill.”

Waste extraction: Heaps of old rubbish, unearthed from the Kelana Jaya dump which was closed in 1996. Through landfill mining, valuable materials such as metal scraps, plastics and rubber can be retrieved from old dumps.

Landfill mining has to be done with care. Aside from foul stench, digging up waste buried for years can be dangerous for workers, points out Zamri Abdul Rahman, general manager of Worldwide Landfills.

“We do not know what hazardous substances lie below. (With the excavation) Landfill gases are released in a short time and can be flammable. The waste should be removed in a procedural manner, cell by cell.

“There must also be a study on the volume of waste, the age and types, as well as surveys on the chemical characteristics of leachate and gas emissions before the landfill is dug up.”

And after all the valuable recyclables have been fished out, whatever that remains has to be safely discarded. “This must go to a sanitary landfill because it is still waste, no matter what. Even if the organics have decomposed, there will still be heavy metals. Fifteen years (the age of Kelana Jaya dump) is unlikely for waste to become inert … 30 years, maybe.”

Besides, it is not enough to just remove the buried waste. Zamri says the surrounding soil must be extracted, too, as it can be contaminated by landfill leachate and gases.

With so many necessary precautions, the cost of landfill mining can run high. Research by Yale University finds that with current technology and prices, the activity is generally not economically viable. The benefits such as revenue from sale of recovered materials generally did not outweigh the costs.

In the West, landfill mining is carried out partly because it frees up much-needed landfill space, thus lengthening their lifespan and avoiding the need to find land to build new dumps. Sometimes, landfill mining is done to remediate poorly designed dumps by enabling installation of protective measures such as liners as well as leachate and gas collection pipes.

In Malaysia, however, landfill mining appears to mask a more lucrative motive – to get the land for development. If done right, this might be acceptable. But so far, there has been no proper landfill mining – it is more like digging out of old rubbish and then dumping that somewhere, anywhere. Tan Cheng Li

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