In Almeria (Spain) it is common for tap water to be used for the irrigation of crops in horticultural greenhouses. This tap water is produced by RO installations, which purify the Mediterranean seawater into drinking water. Water reuse in greenhouses is still being used to a limited extent.
In The Netherlands, rainwater is often used for water recirculation. In addition, low-sodium fertilizers are used. With increasing water scarcity, more and more use is being made of small-scale RO installations in horticultural greenhouses. Brackish groundwater is desalinated to complete desalination and the concentrated brine is returned to the ground. As a result, the groundwater becomes even saltier. This is still being tolerated, but Dutch legislation seems to prohibit this. There are better and more sustainable solutions.
Water Future believes that sodium removal on tap water offers a good alternative. It reduces the sodium content to 0.2 mmol / l in 1 step and has a water yield of 98%. In addition, valuable nutrients in drinking water are retained for the crops.
Growing crops on the effluent water from WWTPs sounds strange, inappropriate and dangerous?
With current water purification techniques, this can become a realistic picture of the future. The microbiological contamination can be filtered out well and organic contamination is captured in activated carbon. The salt content is reduced with the selective sodium removal. With these purifications it is possible to reuse the effluent water as feed water of suitable quality for crops. For more information, see the RVO project cucumber on effluent water.
Various provinces in the Netherlands still have access to good groundwater quality. A low salt concentration, making it suitable as a nutrient solution for crops. Still, the sodium content is too high for water recirculation purposes, resulting in unnecessary drain water and nitrogen discharge. This can be minimized with sodium removal from groundwater. The natural minerals (Calcium, Magnesium, Carbonate) are also retained for the crop.