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Nutrient Recovery from Biogas Digestate by Optimised Membrane Treatment


Biogas plants produce nutrient rich digestates as side products, which are usually used as local fertilisers. Yet the large amount and regional gradients of biogas plants in Germany necessitate management, conditioning, and transportation of digestates, in order to follow good fertilising procedure and prohibit local over-fertilisation. With a membrane-based treatment chain, i.e. centrifugation, ultrafiltration, and reverse osmosis, digestates can be separated into a solid N,P-fertiliser, a liquid N,K-fertiliser, and dischargeable water. Up to now, the high energy demand of the process chain, in particular the ultrafiltration step, limits the economical market launch of the treatment chain. A reduction of the energy demand is challenging, as digestates exhibit a high fouling potential and ultrafiltration fluxes differ considerably for digestates from different biogas plants. In a systematic screening of 28 digestate samples from agricultural biogas plants and 6 samples from bio-waste biogas plants, ultrafiltration performance could be successfully linked to the rheological properties of the digestate’s liquid phase and to its macromolecular biopolymer concentration. By modification of the fluid characteristics through enzymatic treatment, ultrafiltration performance was considerably increased by factor 2.8 on average, which equals energy savings in the ultrafiltration step of approximately 45%. Consequently, the energy demand of the total treatment chain decreases, which offers potential for further rollout of the membrane-based digestate treatment.

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Agricultural biogas plant


Bio-waste biogas plant


Combined heat and power


Extracellular polymeric substances

k :

Consistency factor

n :

Power-law index

R c :

Cake layer resistance

R m :

Membrane resistance


Reverse osmosis




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This research project is supported and financed by the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt). The scientific research was organised at Osnabrück University of Applied Science in cooperation with the company A3 Water Solution GmbH. Furthermore, the authors thank the team of the Department of Water Engineering, Technical University of Berlin, for the LC-OCD analysis.


Funding was supported by Deutsche Bundesstiftung Umwelt (Grant No. AZ 31276).

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Correspondence to S. Rosenberger.

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Gienau, T., Brüß, U., Kraume, M. et al. Nutrient Recovery from Biogas Digestate by Optimised Membrane Treatment. Waste Biomass Valor 9, 2337–2347 (2018).

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  • Biogas
  • Ultrafiltration
  • Nutrient recovery
  • Rheology
  • Energy demand