The horticulture sector also has to comply with increasingly strict regulations regarding their wastewater. In a time that the margins in the sector are not that great. In the Zunurec project, three organizations are looking for a solution. Within two years, this must lead to a (mobile) installation that can be mobilized at the horticulture companies, purifies their water and extracts the nutrients, so that both can be reused again.

BPK (“Belgian Plant Nursery”) is a company that specializes in the cultivation of young vegetable plants for professional horticulture. BPK has more than 200,000 m² of fully automated, heated and exposed greenhouses for this. But it has a problem. These plants naturally need water to grow. This creates various residual water flows on BPK’s site. This mainly concerns rinsing water from sand filters, cleaning water from the ebb and flow systems and excess drain water. Together they form a drainage water. This drainage water contains residues of nutrient nitrogen in the form of nitrate and phosphorus in the form of phosphate, plant pathogens, plant protection products, and occasionally also some zinc and cleaning agent. In the market it is common to buffer this water and then to drain and process it. It is generally not suitable for discharge, neither on grassland nor on sewerage.

General issue
The general problem in the horticultural sector is that, after use, irrigation waters no longer meet the standards for reuse, for example by pathogens, nutrients or for other reasons. So gardeners discharge it. Overall it is about 0 to 10 percent of the irrigation water. There have been many improvements in recent years: the volume of water that is not being used has been seriously reduced. Yet there is usually still a fraction above 50 mg / l nitrate in the drain water, so that it cannot be discharged into the surface water. Then there are two options left: deposit that drainage water on grassland or purify it. More and more attention is being paid to purification, especially for gardeners who work with ebb and flood systems for their irrigation. They have a huge amount of hectares with that system, so they have a lot of water. They could theoretically drop it on grass, but then they would need a lot of land to spread the quantities that they are allowed to spread per hectare according to the law. Or they carry the water to an approved processor – they do that until today. But that costs a lot of money. They look for a solution in purification.

Solution: ZuNuRec
Three organizations joined forces for a demonstration project within the “Flanders Circular” program. They start a project that started in July 2018 and ends in the summer of 2020: ZuNuRec: Purification and Nutrient Recovery and deals with purification with nutrient recovery. There are three partners: BPK, (problem owner), Verhoeve (design and construction of water treatment), and the Proefstation, which forms the link to the wider horticultural sector.

In Belgium and the Netherlands, the Zunurec project is being watched with great interest. The reason is that neither of the countries meets the water quality standards set in the European “water framework directive”. It came into force in 2018. In terms of its water quality, Belgium focuses primarily on nitrogen, phosphorus and groundwater. For the Netherlands, on the other hand, the strict regulation that has been in force since 2018 with regard to crop protection products in burst streams is striking; all nutrients must also disappear from the water there by 2027. ”ZuNuRec combines all things together.

In the greenhouse
The project partners want to purify and reuse the drainage water from BPK and to separate nutrients from it. The recovered nutrients and the purified water are reused during cultivation. The intention is that only a small fraction of drainage water remains, which is moreover sufficiently pure to be allowed to even discharge it into surface water. In a test set-up and cultivation tables, the test station examines the extent to which tomatoes, peppers and cumcumbers can be grown with recycled nutrients.

The test installation
The treatment train essentially consists of a combination of two techniques. The first is advanced oxidation with ozone, hydrogen peroxide and / or ultraviolet, to remove crop protection product residues and disinfect water. The second is ion exchange, with resins, to concentrate nutrients on.

The water that passes through the installation is clean and reusable. The challenge is to be able to get the quality of the fertilizers high enough, through appropriate adjustment and dimensioning of the installation.

The project will have to lead to the construction of a mobile installation that growers can mobilize to treat drainage water from their storage buffers. Growers in Belgium and the Netherlands are willing to invest in purification technology to comply with the legislation, but not to spend money on technology that is out of date within two years. An alternative is to pay for purification and nutrient recovery as a service, via a mobile installation, instead of purchasing such an installation as a product.

The project manager is Petra Geldof | Project manager & calculator | +32(0) 354 00 310 |