Nutrient Recovery from Biogas Digestate by Optimised Membrane Treatment

Biogas plants produce digestates rich in nutrients, yet their uneven distribution across Germany creates challenges for responsible fertilizer use and transport. A membrane-based processing chain—using centrifugation, ultrafiltration, and reverse osmosis—can convert these digestates into separate nutrient products and reusable water, but the high energy demand, particularly in ultrafiltration, remains a major constraint. By examining digestates from numerous biogas plants, this study shows that filtration performance is strongly influenced by the liquid-phase properties and biopolymer content. Enzymatic pre-treatment significantly improved ultrafiltration efficiency, achieving nearly triple the filtration rates and reducing energy consumption by around 45%. These gains enhance the overall feasibility of membrane-based digestate treatment and support its broader deployment.