Modus

Coming clean: the benefits of bioremediation

Using bacteria to cleanse soil doesn’t just remove hazards from contaminated areas, it neutralises toxins in the process

Author:

  • Gela Pertusini

06 January 2023

Flower growing in lab beaker

Illustrations by Miléna Bucholz

In April 2010, an oil rig in the Gulf of Mexico exploded, its wreckage sinking into the sea about 50 miles from the coast of Louisiana. Eleven oil workers were killed but, what Deepwater Horizon is remembered for, is the colossal damage that the subsequent oil spill caused: more than 130m gallons of oil gushed into the sea. Millions of sea creatures were killed immediately and many more were slowly suffocating and starving as their habitats became contaminated.

Deepwater Horizon was the world’s worst oil rig disaster – an event so dramatic that it inspired an eponymous film. It led to a clean-up operation that cost BP, the rig’s operator, $65bn. Several billion of that amount was given in compensation to people whose livelihoods were devastated by the explosion.

But what marked the Deepwater Horizon clean-up was not just the size and extent of the oil spill, it was the use of bioremediation to limit its effects. Traditionally, oil slicks have been “cleared” by skimming and soaking the pollution from the affected area and moving the resultant waste to an area whose ecology is considered less important. Similarly, “dig and dump” methods have been used on contaminated land.

Bioremediation uses microorganisms to degrade hazardous waste materials that are polluting water and land, processing the pollutant and neutralising it by turning it into water and carbon dioxide. The method is used to clean up oil that has seeped into the environment, but it can also be used to combat solvents, heavy metals and chemical waste – anything that is comprised of hydrocarbons.

There are some who argue that traditional practices such as composting or sewage-cleaning reed beds form a type of bioremediation. But industrial-scale bioremediation really took off in the 1970s and 1980s when money – particularly from the US’s Superfund – became available to research how these “natural” techniques could be harnessed and refined.

Gavin Black FRICS was an early adopter of the technology in the UK, setting up a company with other investors in the 1990s to move the science away from the university labs where it had been developed and onto brownfield sites. “The great advantage of bioremediation is that the soil gets cleaned up rather than transferred to another location,” he says. “Dig and dump moves the problem away but it doesn’t solve it.”

It is not hard to see why he was attracted to the potential of the technology: it was a time when green concerns were rapidly moving up the public agenda. The UK – and much of the developed world – was transitioning from an industrial economy but had been left with a legacy of heavily-contaminated land that needed to be treated to make it suitable for other uses. Bioremediation practitioners offer a careful analysis of the type and extent of the pollution but the treatment itself sounds surprisingly straightforward. The soil is dug and aerated – known as “sparging” - and microorganisms (a variety of different bacteria or fungi can be used) are introduced and monitored while they process the pollutants.

If these microorganisms sound as if they might be lab-grown and rarefied, the reality is often far simpler. In one case in Germany, Black recalls that a disused and heavily contaminated ICI factory site needed remediation – the soil expert who attended noticed that there was a pig farm nearby and used the easily-available and accessible pig waste from it to successfully treat the land. 

Professor Graeme Paton is Head of the School of Biological Sciences at the University of Aberdeen and one of the world’s foremost soil scientists (his research won the Queen’s Anniversary Prize in 2021). He believes that events, such as COP26 in Glasgow which put the emphasis on “nature-based solutions”, have provided a showcase for the bioremediation approaches that he has been involved with throughout his career (among his achievements, he has patented a method of water remediation using barley husks, a waste product from whisky distilling). “Bioremediation has always been there,” he says. “A lot of companies have tried to use high-tech solutions to clean up land but bioremediation gives you the chance to solve the problem forever.”

Flower dying in puddle

“A lot of companies have tried to use high-tech solutions to clean up land but bioremediation gives you the chance to solve the problem forever” Prof Graeme Paton, Head of Biological Sciences, University of Aberdeen

His work has taken him to newly-industrialised countries such as China which, less than 40 years into its industrial revolution, is already waging its own war against contaminated land – and successfully so: he says much of the new research in the area is coming from Chinese universities. He was also invited to advise on the clean-up of Kuwait after the First Gulf War when Saddam Hussein’s retreating troops set light to the country’s oil fields. Once the fires had subsided, he was able to remediate the areas to such an extent that, where there was once desert, there are now parks.

“If you think about a tree, the wood is almost a random arrangement of molecules and the carbon within it can be broken down with the right conditions,” he explains. “What we do is condition enzymes to target the carbon [in pollutants].”

The aim is to reduce contamination to a point where the land is judged to be safe enough for a two-year-old child to play on with a less than 1 in 100,000 chance of immediately, or even many years later, developing side effects. “I have a lab full of artificial toddlers’ digestive systems,” says Paton. “It’s a big part of my job… Each site is specific with different levels of contamination, different pollutants.”

The benefits of bioremediation sound like a no-brainer – so why is dig and dump still used?

One of the drawbacks of bioremediation is that it takes time to work – as opposed to dig and dump which, depending on the size of the site, can be achieved in days. Given that many sites spend months in planning limbo, however, there is often an opportunity to treat the soil during this period. The method is also limited to hydrocarbon-based pollutants so won’t work on, say, asbestos.

The second factor might be called “tradition”: some developers are just happier using methods that they are used to and feel that they can control. Gavin Black says that his former company was given a huge boost in Scotland when the Scottish Parliament decided to make it more difficult to dig and dump. 

Different plants growing in a petri dish

“If you think about a tree, the wood is almost a random arrangement of molecules and the carbon within it can be broken down with the right conditions. What we do is condition enzymes to target the carbon in pollutants” Prof Graeme Paton, Head of Biological Sciences, University of Aberdeen

Third is a more endemic problem with the technology: it produces carbon dioxide. Paton argues convincingly that using heavy plant machinery to excavate soil and then carrying it away on lorries to distant landfill sites is likely to produce at least as much CO2 as bioremediation. But a large part of his research is now focussed on locking in carbon to the soil and rendering it harmless to the environment.

And if this can be achieved, it will take the technology from the merely amazing to the absolutely miraculous.

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