Remo landfill site, Belgium

Genetically engineered slugs to chew through landfill and mine precious metals

Genetic engineering could allow scientists to create new lifeforms capable of retrieving materials buried deep within waste sites.

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, believes revolutionary cell technology called Crispr-Cas9 could herald the creation of synthetic 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 globally, 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 tells 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 pinpoint the desired chemical compounds. Specially designed metal-eating slugs could one day be churned out by a new type of biological assembly plant and let loose at waste disposal sites, before being harvested to manufacture batteries, Collins claims – though he goes on to admit 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 says. “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.”

His colleague Professor Richard Kitney says developments in synthetic biology could allow new types of “plastic-eating biological devices” to be created en masse. Non-​biodegradable plastics could be digested and turned into biodegradable material, he says, insisting that the development of this technology is “totally feasible”.

Kitney says: “What we have within landfill is a natural resource, actually, in the same way as oil and gas are natural resources.”

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 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 officials.

Peter Jones, the coordinator of a landfill-mining research project at Belgian university KU Leuven, says: “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 adds: “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; 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, says: “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?” 

Wostyn adds: “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.”

However, Professor Kate Spencer, an expert in environmental geochemistry who has worked with England’s Environment Agency to investigate the impact of historic landfill sites, doubts the practicality of excavating and cleaning up such sites. Though it might technically be possible to do this, she says, it would require an enormous investment of money and would be a giant logistical operation.

Spencer tells E&T: “Some of the landfill sites we have looked at are half a kilometre long and several metres deep. That’s a huge volume of waste material, and it’s hugely variable. We’ve found, from the chemical analysis we’ve done, that levels of pollutants vary hugely over centimetre scales, metre scales and larger scales.

“One of the things that would be really challenging in terms of recycling is that, of all that waste, an awful lot of it isn’t actually of any use. Clearly there are going to be precious metals in there, but they are very dispersed. One of the ways in which technology needs to move forward is in determining how we can get at the material in there which is of value to us and what we do with the material that has no value.”

She adds: “At the moment, all I can think of is you’ve got millions of tonnes of waste and you’ve got to somehow remove that, and then what? Take it to a facility? Are these techniques they are proposing in situ?

“The challenges are in removing the waste. Every piece of equipment that you use will become contaminated. Yes, you can do tests to find out what’s in there, but how many tests do you need to do to accurately find out what’s there?”

She also says there was a “big difference” between modern landfill sites managed according to current environmental regulations and much older sites containing potentially more dangerous materials.

“If your remediation attempts are critical on there being a certain amount of mercury in there, for example, then how do you systematically and thoroughly analyse such a huge volume of material to find out that you have the right level of mercury present?” she asks.

John Collins nonetheless remains upbeat about the prospect of landfill mining in Britain. “If people have the desire to do it, then I would say it is maybe only two or three years off,” he says. “There are already various sensors that can detect interesting materials like arsenic. Detecting something like lithium shouldn’t be too difficult.”

But he adds: “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.”

Collins says other potential applications for bioengineering include creating modified bacteria  to stop fatbergs forming in sewers.  “You could put them in a drink and they could get into sewers that way,” he suggests. He also raised the prospect of using Crispr-Cas9 to create microorganisms designed to chomp through plastics in the ocean or to remove oestrogen from rivers.

He says: “In the same way as we’ve used rational design to make cars go faster or make planes get off the ground, we can do exactly the same with biology.” 

Cleaning up oil-based products

Case study

Professor Richard Kitney from Imperial College London writes:
An example of how landfill waste can be used formed the basis of a project that we performed in our centre.

The system that we developed was designed to maximise the recovery of specific components of landfill waste, namely oil-based plastics. Synthetic biology techniques were used to produce chemical ethylene glycol. This led to developing a synthetic biology recycling system for P(3HB), which is a bioplastic poly-3-hydroxybutyric acid.

This was done at the several-litre scale and, with the help of Imperial College technicians in the fermentation facility, showed the feasibility of industrially scaling the process.

The importance of the project was that it showed that non-degradable waste plastics can be turned, using synthetic biology techniques, into biodegradable plastics that can be used to produce new plastic products. Hence, waste and landfill becomes a source rather than a sink for raw material. As these techniques advance they could be used at local levels, like single households or in a neighbourhood or company, to recycle domestic and industrial waste.

The controversy around Crispr-Cas9

The prospect of genetically engineering small organisms or ‘biological devices’ to help mine landfill sites has led scientists to consider a variety of ethical conundrums.

The technique known as Crispr-Cas9 has “tremendous promise” but also “potential pitfalls,” said Dietram Scheufele, a professor of life sciences communication, speaking in October at a symposium in Hanover on the implications of ultra-​precise genome editing.

Scheufele declared that genome editing “is here to stay, not just in medicine, but also in countless applications in agriculture and food systems”, but added: “The question is how to responsibly roll out various applications in a way that does not unnecessarily slow down innovation.”

Rapid development of Crispr-Cas9 has also fuelled speculation about potential military or other more nefarious uses, including the prospect that it could be used to produce viruses that could be inhaled to create genetic mutations associated with cancer, Scheufele said.

Pilar Ossorio, Scheufele’s colleague and one of a trio of academics from the University of Wisconsin-Madison and the Morgridge Institute for Research who took part in the Hanover conference, said another area of concern centred on use of ‘gene drives’ – a technique that could spread genetic changes within a species to neutralise its ability to be a vector for viruses. She said: “There are safety and environmental concerns about releasing an organism that has a gene drive into the wild. But security experts also worry about a gene drive that could be used to gradually poison a food supply, or enable a mosquito to transmit more rather than less virus.

“Gene editing is unprecedented in that it gives us the capability to make hundreds of genetic changes at the same time, ...in people, other animals and in plants.”

Ossorio added: “We cannot envision all of the directions this technology could take.”

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