Dutch endive grower Leon Duijvestijn sees the legal obligation to purify drainage and industrial waste water, even when discharged into the sewer, as paramount. "It is important that we take this step to make surface water even cleaner. We must be careful what we discharge. Therefore, it is even more important that all growers, without exception, check their ditches to ensure that no drainage tubes discharge there. Especially when companies have been taken over, it is not always clear for the entrepreneur whether, or where there are discharge pipes," the grower tells Glastuinbouw Waterproof.

Crop rotation
Duijvestijn: "Growers must also be honest and close all valves with crop rotation. Waste water should no longer be discharged into the ditch, but removed with a tanker. And you should hold your neighbor accountable even though this is not always easy. In the end, it concerns the improvement of water quality, which benefits everyone."

Central water drainage
Leon and Wilma Duijvestijn grow endives in the ground on 2.1 hectares. Drain water is collected through a drainage and pumping facility in the ground at 0.80 m depth. In spite of a little salt infiltration they manage to re-use 50 percent of the drain water. The other half is discharged into the Centrale Afvoersysteem Drainagewater (CAD) [Central Drainage Water System]. This separate sewerage system was installed in the early 80s at the initiative of entrepreneurs in different horticultural areas in the western part of Westland.

Duijvestijn is a member of the Vereniging Afvoer Drainagewater Zanddijk [Association of Drainage Water Drainage Zanddijk]. This, and five other associations are linked to the overarching Stichting Verbetering Oppervlaktewater Westland (SVO Westland) [Foundation Improvement Surface Water Westland]. These total about 350 hectares of greenhouse.

Purification system
The foundation has signed the associations up as collectives, because it sees good opportunities to centrally purify the discharged water. A feasibility study was carried out as to the removal of plant protection products, fertilizers and heavy metals. The industrial waste water is collected in silos at a central collection point. There, buffering and sedimentation takes place, whereby the sediment is thickened and discharged. An active carbon filter then removes the plant protection products and biologically treats the fertilizers and the heavy metals. The first part already settles in the buffer silos. Only the salt remains in the water, but that is no problem because the treated water is discharged into the sea.

Collective solutions
"For an individual company to purchase a purification system requires a considerable investment. It is cheaper and better to do it together. That’s why we signed up for the collective," the grower explains.

Under certain conditions, collectives for the treatment of residual water can get a postponement of the individual purification duty commencing January 1, 2018. The postponement will then apply for a maximum of three years, latest until January 1, 2021.