The article describes a pilot-industrial system developed by SIGMA Water Group in Spain for the treatment of the liquid fraction of digestate from a biogas plant co-digesting cattle manure and fruit residues. Through ultrafiltration (UF) followed by reverse osmosis (RO), the liquid digestate is separated into a purified water stream and a nutrient-rich concentrate. The purified water meets high quality standards, while the concentrate is valorised as an agricultural product (potential fertiliser or soil application). The system demonstrates the feasibility of membrane technologies for digestate valorisation at scale and contributes to closing nutrient loops while reducing environmental impacts.
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