Is underground irrigation a solution for water shortages?

This season it was dry again, which meant that the theme of 'water scarcity' came up for the umpteenth year. Can underground irrigation with treated sewage water change this? Researchers at the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam think so. "The soil has to act as a natural filter."

The group of researchers is looking at whether treated sewage water in the agricultural sector can be reused through irrigation via groundwater. "At the moment, treated wastewater is already unconsciously reused, namely via above-ground irrigation. This is because sewage treatment plants discharge very large quantities into surface water and rivers, among other things," says PhD student Dominique Narain-Ford who is involved in this research. Evidence shows that conventional treatment plants cannot remove all micropollutants. "As a result, the treated sewage often still contains residues of medicines or a wide range of chemicals."

According to Narain-Ford, this is particularly a problem in dry summers. "The surface water is then fully used by the farmers for above-ground irrigation and this therefore results in unintended exposure to these micro-pollutants." The team is investigating whether underground irrigation with treated sewage water will solve this problem. "Underground systems can hold water for longer, giving the soil a chance to filter, buffer and break down the chemicals left in the wastewater." However, exact figures on this are not yet known. "We have collected samples and that data is currently being worked out."

Not possible everywhere
There are several countries that use underground irrigation or the use of treated sewage through above-ground irrigation (including the Middle East, Africa and the Mediterranean countries), but the combination of treated sewage and underground irrigation is new. "This is mainly due to the fact that wastewater is not yet optimally used and an existing infrastructure (the irrigation-drainage system) must be in place," explains Narain-Ford. This also means that innovation is not possible everywhere. 

In addition, there are sufficient areas in the Netherlands where water cannot be retained properly. "For underground irrigation, the groundwater levels must be above the pipes, otherwise nothing will be stored. If a field does not allow this, then underground irrigation is not possible. Of course you can still consciously use the treated sewage water with other above-ground techniques." Narain-Ford explains.

Long-term research
All in all, much is still unclear. "The first results are positive, but we still have a lot of research to do. The project started in 2015 and I joined in 2018. The goal is to complete it in 2022. Then, for example, it should be clear to what extent the soil acts as that natural filter," concludes Narain-Ford.

Kimberly Baker

Kimberly Bakker is an all-round editor at Boerenbusiness. She also has an eye for the social media channels of Boerenbusiness.

k.baker @boerenbusiness. Nl

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