Science - April 26, 2018

Bacteria can purify Utrecht park soil

Roelof Kleis

How can you train bacteria to most effectively cleanse the polluted soil of Griftpark, a park in Utrecht? Wageningen researchers will be figuring that out.

© Het Utrechts Archief

Griftpark is attractive, green and a popular place for recreation. But things don’t look so good underground. The soil is contaminated by aromatic hydrocarbons from a gasworks that used to be on this site. In the 1980s, the park was one of the most polluted sites in the Netherlands. Instead of excavating the soil, the decision was made to close off the land with a 50-metre deep wall, says environmental technology specialist Tim Grotenhuis. Since then, the groundwater in the resulting basin has been pumped up to prevent it from seeping into the surrounding area.

Griftpark’s soil contains chemicals such as benzene and xylene from the gasworks that once stood here.
Griftpark’s soil contains chemicals such as benzene and xylene from the gasworks that once stood here.

That pumping operation could in principle go on for ever and it costs around 100,000 euros a year. Utrecht wants to see if there might now be a cheaper method. And there could well be, says Grotenhuis: the bacteria in the soil could eat up the pollutants. The park has bacteria that thrive on chemicals such as benzene, toluene, xylene and naphthalene, the principal contaminants in the soil. Grotenhuis says there is no doubt about that. ‘Lesson 1 in microbiology is that all bacteria are everywhere. And lesson 2 is that the environment
determines which microorganism or group of microorganisms gets the upper hand.’

Wageningen PhD candidate Lisanne Keijzer will be investigating the breakdown of the pollutants by the microorganisms. Grotenhuis: ‘We will take soil samples from the site and do experiments in the lab. We will study how we can optimize the breakdown rate by adjusting the right parameters.’

According to Grotenhuis, at this stage the aim is a proof of principle, to show that it is possible. Meanwhile, researchers at Deltares are getting a picture of the soil’s current state and Utrecht University is studying the groundwater flows. The ultimate goal is to be able to stop the expensive pumping. But that will only be possible if the bacteria can dispose of so many contaminants that nothing more seeps away along with the groundwater through the bottom of the basin. Grotenhuis: ‘The environmental conditions are probably not optimal for this at the moment. But you can create optimal conditions by adding substances in the right places.