Mechanical separation
Nutrient Removal and Recovery from Digestate: A Review of the Current Knowledge
Digestate is a byproduct of anaerobic digestion, which can be considered waste or a product of potential use for the chemical industry or agriculture. In either case, the digestate must usually be treated prior to being disposed of or valorized. This review describes digestate processing technologies and their specific characteristics. Nutrient recovery and removal from digestate can be achieved through mechanical, physicochemical or biological processes. Available and potential digestate treatment techniques are presented. The complexities of the technologies available, legislation, the agronomical value of the digestate and the economic value of the process mean a decision support tool is required to help managers choose the best digestate processing technology. To ensure adequate analysis, the whole biomethanization project should be integrated in the use of these decision support tools. The objectives and limits of some of the currently available tools are analyzed at the end of this review.
Nutrient recovery from digestate: Pilot test experiments
A pilot-scale study tested several technologies to treat biogas digestate— the residue from anaerobic digestion of dairy, animal, and some crop wastes—so that nutrients can be recovered and the material can be reused. The digestate was processed through microfiltration, ultrafiltration, reverse osmosis, selective electrodialysis, and UV/ozonation. Early filtration steps removed over 80% of solids and large organic molecules, while reverse osmosis removed nearly all remaining dissolved substances, producing clean water suitable for reuse. Selective electrodialysis recovered over 95% of ammonium and potassium and about 55% of phosphate, 75% of which was turned into struvite, a valuable fertilizer.
Nutrient-recovery-from-digestate-Pilot-test-experiments.pdfDigestate Valorization: Turn Waste into Premium Organic Fertilizer & Energy
The article explains how digestate — the wet by-product of anaerobic digestion — is being transformed from a bulky waste into a premium organic fertiliser and energy source. It highlights multiple upgrade technologies such as mechanical dewatering, thermal drying, pelletisation, struvite precipitation and water recycling, allowing facilities to recover nitrogen, phosphorus, potassium and also reuse water.
It emphasises both the economic benefits (reduced disposal costs, revenue from energised processes, premium pricing for processed products) and the environmental advantages (lower greenhouse gas emissions, less reliance on synthetic fertilisers, conservation of finite resources, improved water quality) of such valorisation paths.
The article suggests the future of digestate lies in its integration into circular-economy models: waste becomes input for high-value outputs, helping to close nutrient loops while enhancing sustainability.
Read the full article here
Nutrient Recovery by Biogas Digestate Processing
This report reviews various approaches for processing of biogas plant digestate for the purpose of nutrient recovery. It covers both established and emerging technologies and assesses technical performance and where possible economics. Techniques for nutrient recovery from digestate are developing rapidly and aim to improve nutrient management in agriculture and in waste treatment systems.
The report is aimed at biogas plant developers and operators as well as agriculture policy makers and was produced by IEA Bioenergy Task 37. IEA Bioenergy Task 37 addresses challenges related to the economic and environmental sustainability of biogas production and utilisation.
Read the full report here
Treatment of Manure and Digestate Liquid Fractions Using Membranes: Opportunities and Challenges
This review examines how membrane technologies can be used to process nutrient-rich manure and digestate liquids, which often cause membrane fouling due to their high content of organic matter, solids, and mineral compounds. It summarizes the key physico-chemical properties of these effluents and explains how different solid–liquid separation methods interact with these complex variables. The paper outlines the major factors influencing membrane fouling, along with approaches for inspecting membranes and analyzing foulants. It also discusses how feed characteristics, operating conditions, pH control, flocculation–coagulation, and cleaning strategies affect system performance. Finally, it highlights techniques for recovering nutrients such as ammonia-nitrogen and phosphorus, as well as removing heavy metals from farm effluents.
Treatment-of-Manure-and-Digestate-Liquid-Fractions-Using-Membranes-Opportunities-and-Challe.pdfNutrient 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.
Nutrient-Recovery-from-Biogas-Digestate-by-Optimised-Membrane-Treatment.pdfNutrients recovery from anaerobic digestate of agro-waste: Techno-economic assessment of full scale applications
Sustainable fertilizer production—especially for phosphorus—will be a major challenge in the coming decades, making nutrient recovery from agricultural, urban, and industrial organic wastes increasingly important. This study evaluated five full-scale technologies used to recover nutrients from anaerobic digestate in farm-scale plants, including drying with acid capture, stripping with acid capture, and membrane-based separation. All systems achieved strong recovery performance, with average nitrogen and phosphorus yields exceeding 50%. The techno-economic analysis showed notable differences among the technologies: membranes produced high-quality water and reduced digestate volume, drying was limited by available heat, and stripping faced issues with suspended solids. Overall, the systems showed comparable costs, similar to those reported in other European applications, highlighting their practical feasibility.
Nutrients-recovery-from-anaerobic-digestate-of-agro-waste-Techno-economic-assessment.pdfValorisation of digestate: Characteristics, products, processes and potential
Anaerobic digestion (AD) is an important technology for renewable energy production and waste management, but it also generates large volumes of digestate that must be effectively managed to realize its full sustainability potential. This review examines the key characteristics of digestate and how they influence opportunities for its valorisation into useful products. It assesses current technologies, including separation methods and advanced processing pathways, and discusses their technical and economic implications. Policy and regulatory considerations are also highlighted. Overall, the review provides guidance for researchers, industry stakeholders, and policymakers working to advance circular economy strategies.
Valorisation-of-digestate-Characteristics-products-processes-and-potential.pdf