In the quiet town of Jülich, Germany, where innovation meets industry, a team of researchers at the NOWUM-Energy Institute of FH Aachen is turning a challenge into opportunity. Dheeraja Winter and her colleagues have zeroed in on a pressing issue for paper recycling mills: how to efficiently separate water from the digestate left over after processing short-fibre residues. This isn’t just about waste management—it’s about unlocking a new stream of reusable water and reducing freshwater consumption in an industry that guzzles millions of litres annually.
Digestate from paper recycling is a tricky substance—part liquid, part solid, and packed with organic matter. Traditional methods like simple sedimentation (letting gravity do the work) only skim the surface, recovering a fraction of the liquid while leaving behind a sludge that’s costly to manage. Winter’s team tested seven different approaches to dewatering, from chemical aids like iron(III) chloride and polyDADMAC to mechanical methods like centrifugation. The results, published in the journal *Recycling*, reveal a clear winner: centrifugation paired with polyDADMAC delivered the highest liquid recovery—up to 690 grams of water per kilogram of digestate—while keeping solids low. “The mechanical force combined with the right chemical additive fundamentally changes how we approach this separation,” Winter explains. “It’s not just about removing water; it’s about doing it in a way that makes the liquid fraction reusable.”
For paper mills, this could mean a double win: cutting down on freshwater intake and reducing the volume of waste they need to dispose of. The study also found that key pollutants like chemical oxygen demand (COD) and phosphorus were largely stripped from the liquid, making the recovered water cleaner and easier to treat further if needed. Nitrogen and ammonium levels, however, remained variable, suggesting that additional filtration or treatment steps might still be necessary depending on the mill’s specific needs.
The commercial implications are significant. Paper mills are energy-intensive operations, and water is both a critical input and a waste stream. By improving dewatering efficiency, mills could lower their operational costs, comply more easily with environmental regulations, and even generate a new revenue stream by selling or reusing the recovered water. Winter’s work suggests that the future of digestate management in paper recycling isn’t just about disposal—it’s about transformation. “This isn’t just a step forward in waste management,” she says. “It’s a leap toward circularity in an industry that’s been linear for too long.”
As the paper industry grapples with sustainability pressures, research like this—published in *Recycling*—could set the stage for broader adoption of advanced dewatering techniques. The next frontier might involve integrating these methods with membrane filtration or anaerobic digestion to create closed-loop systems where water and energy are continuously recycled. For now, Winter’s team has given mills a practical tool to turn a problematic byproduct into a resource. The question isn’t whether they’ll take it—it’s how fast they can adapt.