A Circular Partnership: From Wastewater to Greenhouse Growth
A circular collaboration between water management and greenhouse horticulture shows how residual streams can be turned into valuable resources — with a direct impact on sustainability and supply security. Watch the video and read the interview with Water Authority De Dommel and Fresh Valley.
Less Fossil, Less Vulnerable
CO₂ has long been seen as an unavoidable by-product of wastewater treatment. But through innovative partnerships, this residual stream is now being given a second life. Water Authority De Dommel is leading the way: the CO₂ released during their sludge digestion process is now being reused in greenhouse horticulture. A true win-win: the water authority finds a circular solution for what would otherwise be waste, and growers gain access to a stable and sustainable source of CO₂.
At first glance, Water Authority De Dommel and vegetable grower Fresh Valley may seem worlds apart — but they share a strong commitment to circularity. Their paths crossed about a year and a half ago through AquaMinerals, an organisation that helps Dutch water authorities find new purposes for the materials released during water purification.
Bas Peeters, board member at Water Authority De Dommel, focuses on innovation and circular solutions: “We see it as our responsibility to handle the residual streams from water management in a meaningful, sustainable way.”
A Green Solution
At Water Authority De Dommel, smart reuse of residuals is part of daily operations. Grass cuttings, for example, are used as raw material for insulation boards, and now the CO₂ from sludge digestion is also being put to good use.
“We convert part of it into biogas at our green gas facility in Tilburg,” Bas explains. “That plant supplies 100% renewable gas to four thousand households. There’s enormous potential for using CO₂ in various applications — especially since our source is continuous and always available.”
High CO₂ Concentrations Required
Recently, the CO₂ from Water Authority De Dommel has also been deployed in the cucumber greenhouses of Fresh Valley. Sam van Duifhuizen, board member at Fresh Valley, explains: “Our cucumbers are sold in almost every Dutch supermarket — in all shapes and sizes. We produce the standard variety, but also the mini snack cucumbers you often see in children’s lunch boxes. We grow about 50 million of those per year. ”That scale of production requires a steady and elevated supply of CO₂. Plants grow through photosynthesis, using sunlight, water, and CO₂ to produce sugars — and eventually cucumbers,” Sam continues. “That’s why we maintain elevated CO₂ levels in our greenhouses to speed up growth. We measure concentrations in ppm — parts per million. Outdoor air has about 420 ppm, while inside our greenhouses we aim for 500 to 700 ppm.”
The Impact of the Energy Crisis
When CO₂ levels drop below 400 ppm, Fresh Valley’s production is significantly affected because the plant’s photosynthesis becomes less efficient. “That happened during the early days of the war in Ukraine,” Sam recalls.
“Raw materials became scarce, prices skyrocketed, and the CO₂ sources we used before weren’t very circular. Much of it comes from fertilizer production, which relies heavily on fossil gas.”
A Continuous Stream of CO₂
The CO₂ from Water Authority De Dommel offers multiple advantages. “Because this CO₂ has a cleaner origin, it aligns better with our values,” Sam says. “At Fresh Valley, we make green choices wherever possible. We use natural pest control and work with beneficial insects instead of chemicals. This circular CO₂ source is the missing piece in our sustainability story. ”Another major benefit is the guaranteed continuity of supply. “As long as people exist, there will be wastewater — and therefore CO₂,” Sam concludes. “That means no matter what happens in the world, our cucumbers can keep growing.”