Constructed wetlands pilot project

 

The motto of Water Nexus is ‘salt water where possible, fresh water when needed’. Different industries produce brackish to salt waste water streams, that possibly can be reused by either the industry itself or by for instance agriculture. However, this water often needs to be treated before reuse. A treatment option is the use of constructed wetlands (CWs). CWs are man-made wetland systems, isolated from the natural environment, that employ the natural treatment capacity of natural systems for the removal of contaminants from water streams. ​Throughout the world, CWs have been employed as an alternative for or in addition to different forms of domestic- and industrial wastewater treatment. CWs are often considered to be a suitable (secondary) wastewater treatment option because of their low maintenance effort and costs, low energy requirements and their integration in the landscape.

 

The development of constructed wetlands (CWs) for water treatment has a central place within the Water Nexus project. CWs can be combined with other water treatment technologies developed within Water Nexus to come to the most optimal water treatment technology train. In addition, CWs provide the required space and environmental conditions for the installation of plant-microbial desalination cells. CWs also provide opportunities for biobased production. Furthermore, CWs can function as a water storage area. However, this demands proper modelling of the on- and off site water streams and land use.

 

The main function of the CWs to be installed is the natural treatment of the saline industrial waste water streams. The suitability of CWs for waste water treatment is a result of various contaminant removal processes occuring in CWs simultaneously. Anaerobic and aerobic biodegradation, photodegradation, plant uptake and adsorption to the soil matrix are the main processes responsible. The dominating removal process in a CW depends on its configuration. For instance, photodegradation occurs mainly in open water ponds where sunlight can enter the water directly, while aerobic and anaerobic biodegradation can be found in batch fed vertical subsurface flow CWs where air is allowed to enter the CW. In addition, the removal efficiency of CWs are influenced by the choice of substrate, vegetation, hydraulic retention time and the climatological circumstances.

 

Next to the Wageningen University, various 12 m3 CW basins with direct connection to the laboratories are installed (figure 1) to test their applicability for the treatment of saline industrial water streams provided by the different industrial partners from the Water Nexus consortium. These water streams contain different chemicals to maintain a proper functioning water circuit on site as corrosion inhibitors, biocides and antiscalants. In earlier research, these compounds have shown to be susceptible to different removal pathways occurring in the CWs. However, this was never tested in the context of saline industrial wastewater. Hence, various CW configurations have been designed to test the removal of these residual treatment chemicals from the different saline waste water streams. The objective is to find the removal efficiency of different removal pathways for a set of target components and this way find the most optimal CW design. Most likely, this design will consist of various CW configuration, and therefore different sequences of these configurations will be tested. Therefore, separate small scale CW inserts with different configurations were developed and installed in the big CW basin in order to be able to be flexible with the CW sequences in the future (figure 2-12) .

Figure 1. Demo CW basins at the start of the project

Figure 2. Different custom made CW inserts

Figure 3. Transport of the small insert to the larger basin (on the left)

 

 Figure 4-9. Installing the CW sequences

Figure 10. Wetland set-up finished

 

Figure 11. Determining optimal plant distribution

Figure 12. Planting Phragmites australis