Wetlands - the way of water
“How can we innovatively make water use more sustainable?” is a question we asked ourselves frequently during the contract negotiations with Evides. There, wetlands emerged as a natural tool for purifying water. Two pilots are already in progress and expectations are high. But what do these wetlands actually do? And what exactly is the path taken by water? More on that in this article.
The way of water
The infographic below shows the path water takes. Niels Groot, Water Specialist at Dow, explains: “We use treated wastewater from the municipality of Terneuzen (top left of the infographic) and treated wastewater from Dow's own wastewater treatment plant (middle right) that goes towards the wetlands. Together with the rainwater that is collected at the Dow site (top right), we want to achieve that the biological activity in the wetlands is stabilized and also that as much nitrogen and phosphate as possible is removed from the water. We can then use a series of treatment steps (including desalination) to bring this water up to quality standards so that it can be used again in our plants. The trick with wetlands is that the water is so stable that we can then do the steps much more effectively with significantly less energy and chemicals.”
The functioning of a wetland
A wetland is an inventive and functional piece of nature. Niels: “The water that flows into a wetland is distributed underground in a system that contains brown porous clay granules. Bacterial populations develop in these brown granules and these bacterial populations can break down organic waste products in the water. This prevents those organic substances from depositing on the desalination membranes (very fine filters) in the follow-up steps and the need for frequent cleaning. In addition, reed plants are planted in the substrate which ensure that, among other things, the breakdown of polluting components takes place in the root zone.” With this, wetlands ensure that much more wastewater can be reused.
The potential benefits of a wetland in a nutshell
Because of the wetlands, fewer chemicals and energy are needed in the treatment process. Niels: “Without the wetlands, the filters would clog up much faster in the subsequent steps of water purification. Because that purification takes place at the molecular level, water that is too dirty would cause problems very quickly.” Furthermore, the wetlands are also useful for storing excess surface water. This can be of value in the summer during longer droughts. “And”, adds Niels: “A nice side effect is that this piece of nature also stimulates biodiversity in the area, but the most important aspect remains that through wetlands we can scale up the reuse of water, and thus greatly reduce the use of potential drinking water.”
“The pilot has been running for 1.5 years now. This summer it will be completed and we will evaluate the results and see if it is also economically valuable for Dow,” said Jeroen Tap, Energy Contracts Manager at Dow. “So that decision will probably be in the fall of 2021, after which we can start building the wetlands and the associated linked treatment technologies.”