A UK landfill site operated by Veolia

Genetically engineered slugs ‘could help mine landfill sites’

Image credit: Veolia

Recovering valuable metals buried in amongst municipal and industrial waste could be big business in future, a government-backed UK research centre says – and 'bioengineering' could help kick start the process

Landfill sites might one day be able to be mined for valuable metals using genetically engineered slugs or repurposed microorganisms, scientists pressing for the commercialisation of synthetic biology say.

Dr John Collins, commercial director of UK research centre SynbiCITE, said revolutionary new cell technology called CRISPR-Cas9 could herald the creation of new manmade biological systems or ‘biocatalysts’ to digest waste and convert it into useful products.

CRISPR-Cas9, described as the most precise and versatile method for genome editing ever developed, is already being used to forge new biomedical and pharmaceutical tools. The process is opposed by some who believe it will amount to scientists ‘playing God.

SynbiCITE has received tens of millions of pounds from the British government to accelerate this type of genetic innovation and position the UK as a global leader in the field of bioengineering. One application for the technology might be in helping to realise the so-called circular economy vision entailing treating waste as a potentially valuable resource. Research into ‘biometallurgy’, whereby bacteria are designed to selectively recover certain metals, is ongoing at several scientific institutions worldwide, though insiders say it is currently “at a low TRL [technology readiness level]”.

“Biomining is going to be a thing of the near future,” Collins told E&T. “Without a doubt we have to do it because we have such limited natural resources.”

Large quantities of lithium that could be reused to create batteries for electric cars lies buried deep within old landfill sites in the UK. It could be reclaimed, potentially with the help of genetically enhanced organisms.

A synthetically produced “broth of cells” designed to change colour on contact with certain metals could be poured into mounds of waste to help locate the desired chemical compounds. Specially designed metal-chomping slugs could one day be churned out by a new type of biological assembly plant and unleashed at waste disposal sites, before being harvested to make new batteries, Collins claimed – though he later admitted this idea might seem far-fetched.

“The slugs thing is a whole genetic splicing thing that might never happen, but it’s a lovely thought,” he said. “In terms of actually having an organism that you create - a bacteria that biomines - there are already people doing that on a very small scale in gold mines.”

Mining of landfill sites using more conventional methods is already being practised in some countries, most notably Belgium, which is home to what is believed to be the largest landfill mining project anywhere in the world.

Techniques used to mine municipal landfill sites containing household waste differ dramatically from those used at sites that contain industrial residue. Inventories of the contents can be completed using techniques like sonar or radar, but legal issues concerning ownership and land rights can present challenges. The fact that numerous ex-landfill sites in Britain have been capped off and turned into public parks could also put a brake on excavation in the UK. In addition, efforts to push landfill mining at a pan-European level are understood to have faltered because of an alleged queasiness about radical environmental solutions among top-level European Union bureaucrats.

Peter Jones, the coordinator of a landfill mining research project at Belgian university KU Leuven, said: “As well as policy, economics and technology, there is the whole legal issue and the ‘nimby’ syndrome. With a lot of the landfill mining projects that have been investigated over the last decade, the technology is ready, and in some cases there is a valid business case, but the problem is the lack of permits that have been issued because of objections from a very small minority of local people.”

He added: “People might say they don’t want landfill mining to happen in their back yard, but that means these raw materials then have to be sourced from somewhere else. They might have to come from China and will have to be transported all the way to Europe.

“They have a major environmental burden locally in China in terms of specific metals, so we are just being very hypocritical, because there is a much larger environmental burden now with primary raw materials being transported over such long distances.”

Piet Wostyn from KU Leuven’s molecular design and synthesis unit, said: “Landfill mining is already taking place. It has been shown to work. The question is: How can we make sure it is an economically sound model?”

He added: “What we want to do with the landfill sites, ultimately, is to clean them up completely. We want to take out everything, recycle what can be recycled, get out the energy that is in the waste and with the final fraction containing interesting materials like metals, get that out and convert what is left into new products like green cement or plasma rock.”

Back in the UK, Collins remains hopeful that landfill mining could soon take place in Britain.

“It all depends on who wants to do it,” he told E&T. “If people have the desire to do it, then I would say it is maybe only two or three years off. There are already various sensors that can detect interesting materials like arsenic. Detecting something like lithium and lithium compounds shouldn’t be too difficult.

“We know there is lithium in these sites. You can look at the degradation of the batteries and all those things that have been put into landfill – which is an acknowledged problem – and you can look at the lithium content in the area and measure it.”

But he added: “At the moment people are entirely complacent about landfill and don’t really know about biomining. It’s a case of out of sight, out of mind.”

He said other potential applications for bioengineering include dealing with fatbergs in sewers. Specially modified bacteria could be put into sewers to stop these conglomerations of cooking fat from ever forming.

“You could put them in a Yakult-type drink so people could drink them and poo them out and they could get into sewers that way,” Collins said.

He even raised the prospect of using CRISPR-Cas9 to create microorganisms designed to chomp through plastics in the ocean and convert them into byproducts that would cause less harm to marine life, or to remove the hormone oestrogen from rivers where it is said to have accumulated because of use of the contraceptive pill.

Collins said: “In the same way as we’ve used rational design for all sorts of things – to make cars go faster or make planes get off the ground – we can do exactly the same with biology.”

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