A virtually closed circular cultivation of tomato, sweet pepper and cucumber; the new ‘Waterstreams’ webtool helps Dutch greenhouse growers make this a reality. “If the 4500 growers use the tool correctly, they will discharge less than five per cent of the water,” says scientist Erik van Os of Wageningen University & Research, Greenhouse Horticulture business unit.
Nearly 90 per cent of Dutch greenhouse horticulture takes place in greenhouses where major vegetables such as tomatoes, peppers and cucumbers are grown on substrate. This often comprises mineral wool and coconut fibres; lightweight material that is replaced after one year and fully reused or composted. Because the substrate contains no nutrients, the horticulture sector relies on a smart system of water in which an exact dosage of nutrients and, occasionally, plant protection products has been dissolved.
Even less water
“Many growers manage to keep a lot of water in the cycle,” explains Erik van Os, greenhouse horticulture scientist at Wageningen University & Research. “Nonetheless, some five to 15 per cent of the water is discharged into the sewers or surface water as growers suspect it is no longer useable – for instance because it contains too much sodium.”
The Wageningen webtool ‘Waterstreams’, launched in early November, gives growers insight into the water streams in their greenhouse and the cause of their discharge. “By varying the settings in the tool, growers can see how they can achieve a zero per cent discharge. Filtered flush water is now often discharged via an automatic process without the grower knowing exactly when and how much. The webtool shows users the actual volume and the fact that a discharge is occurring every few days. In addition, the tool allows them to choose an option in which the flush water is reused. This way they can see the effects and gain more insight into the necessary changes. Across the line this can reduce the emissions via water in horticulture from 15 to five per cent, or less.”
This benefits both the environment and the growers themselves, as they have to purchase less lost water and fertiliser or can start using a smaller purification system thanks to the results of the tool and its specific settings.
Complying with future regulations
Another factor is that the sector can expect even stricter regulations in the future. From 2018, growers can only discharge water after using a purification system that is certified for removing 95% of all pesticides. And from 2027 discharge water can no longer contain any nitrogen or phosphate. “This means that the horticulture industry will have to recirculate more water and require more equipment for maintaining water quality,” Van Os continues.
The webtool gives horticulturalists a greater insight into the volume and quality of their water streams, and helps them make investment decisions; for example, on whether to purchase purification equipment, storage tanks for rainwater or equipment for the reuse of the flush water from the filters in their greenhouse.
In essence, the webtool is a simple way for growers to enter information after which a smart algorithm performs the complex calculations. As the horticulture sector has already paid for the research work, the tool is available for free via the Wageningen University & Research website.
“Zero emissions in greenhouse horticulture along with a virtually circular greenhouse horticulture sector are within reach,” says Van Os. “The greenhouse is increasingly becoming an energy supplier instead of a large-scale consumer of natural gas, the substrate has a second life, and the process water is infinitely reused. The final step in closing the water cycle is reclaiming all evaporation, which is already possible in closed greenhouses. It also has many energy benefits, although this is not yet feasible from an economic perspective.”