Nature as a water filter
“How can we innovatively make water use more sustainable?” is a question we asked ourselves frequently during together with our partner in waterprojects Evides Industriewater. There, wetlands emerged as a natural tool for purifying water. Wetlands are swampy areas rich in natural vegetation - are used as a natural water filter. This purifies wastewater from the local industrial and domestic wastewater treatment plants and provides proper pretreatment for a downstream desalination step.
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.
Wetlands at Dow Terneuzen
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.
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.”
Two 350 m² wetlands have been created on the site of Evides Industriewater, on the border of the industrial park where Dow has several plants. The plant roots and microbes in the soil must ensure the biological stabilization of brackish wastewater before it is desalinated. The quality of the water is closely monitored via a newly built research location near these two test wetlands and the impact on further purification into demineralized water (mineral and salt-free water) is investigated. A special feature of this application is that additional functionality has been added to these natural systems through additional aeration, among other things.
At the same time, in the Braakman-Zuid area, in cooperation with local farmers, we are investigating the possibility of storing rainwater and polder water underground. In this way, reserves can be made available during droughts. This is an aspect that, certainly with the increasingly dry summers, can contribute to reducing the need to use water that is also suitable as a source of drinking water. Both projects receive financial support from the Deltafonds [Delta fund] and the EU Interreg Twee Zeeën [Two Seas] program respectively.
If the pilot is successful, it can be expanded to 6 to 8 hectares of wetlands. The result: a lot more (re)use of treated wastewater and a lot less use of Biesbosch water. And that is important, because Biesbosch water is an important source for the production of drinking water. In addition, the quality of the cooling water will be improved to such an extent that Dow will need less water and chemicals in the cooling towers.
