Utrecht University: Toxin-degrading bacteria Griftpark mapped

Scientists from Utrecht University have identified the bacteria that can biologically clean up the groundwater in the Griftpark in Utrecht. Half of the bacteria in the bioreactor turn out to be biodegrading bacteria.

For 20 years, the polluted groundwater of the Utrecht Griftpark has been purified biologically by the city of Utrecht, Deltares and Royal Haskoning in a bioreactor in the north of the city. This method of bioremediation works very well: almost all pollutants are broken down by bacteria in the bioreactor.

Highly specialised and multiplied
However, it was still unclear which bacterial species were actually responsible for this rapid decontamination. This has now become known because bioinformaticians and microbiologists from Utrecht University were able to determine the composition of the micro-organisms in both the groundwater and the bioreactor. Researcher Tina Hauptfeld: “Most of the biodegrading bacteria belong to the Burkholderiales group. In the bioreactor, they make up 50% of all bacteria present, whereas in the polluted water that enters the bioreactor, they are only 0.3% of all bacteria. Over the years, they have specialised and multiplied in the bioreactor under the favourable conditions of the right temperature, acidity and sufficient oxygen. Now in the reactor they remove almost all pollutants from the water within 24 hours.”

Due to the strong specialisation and multiplication of the bacteria in the bioreactor, they now remove almost all pollutants from the water within 24 hours.

Tina Hauptfeld
Anti-bulking reactor
Hauptfeld was able to trace which species the biodegrading bacteria belong to by analysing the DNA present in the bioreactor in one go. “The result is the ‘metagenome’ of the entire community of microorganisms together, which you can then pick apart again with the computer.” The fact that these bacterial groups were able to make up such a large proportion of the total bacterial community has everything to do with the type of bioreactor. “In a normal reactor in which bacteria are reused, a thick layer of bacteria develops over time. The bioreactor that purifies the water from the Griftpark is a so-called ‘anti-bulking reactor’, where the bacteria do not stick together and the biomass can therefore easily be reused.”

Old gas plant
In the 1980s, the Griftpark in Utrecht became known for the heavy soil pollution caused by the remains of a gas factory and later a rubbish dump from the 19th and 20th centuries. The soil contamination was so severe that the park was enclosed underground by an isolating wall 64 metres deep to prevent the toxins from spreading. Research leader and metagenomics expert Bas Dutilh: “Otherwise there was a risk that the contaminants would end up in Utrecht’s drinking water. To ensure that the polluted water could not penetrate further into the soil via rainwater, it was continuously pumped away.”

Now we know which group of bacteria is responsible for the rapid decontamination, it may be possible to start up such a process in other places where groundwater was polluted by the oil and gas industry.

Bas Dutilh
Bacterial transplant
Now that it is known which group of bacteria is responsible for the rapid decontamination, the researchers believe it might also be possible to transplant the good bacteria from the Utrecht bioreactor to other places where groundwater polluted by the oil and gas industry needs to be cleaned. Dutilh: “It may then be possible to start up such a process much faster because the right bacteria are already abundantly present. It’s like bread dough, parts of which you pass on to bake a loaf of bread without having to add more yeast.”

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