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125 Dr. rer. nat. Brigitte Kempter-Regel Phone +49 711 970-4128 brigitte.kempter-regel@ Dr. rer. nat. Ulrike Schmid-Staiger Phone +49 711 970-4111 ulrike.schmid-staiger@ Contact Funding We would like to thank the German Federal Ministry of Educa- tion and Research for funding the project “EtaMax – Mehr Bio- gas aus lignocellulosearmen Abfall- und Mikroalgenreststoffen durch kombinierte Bio-/Hydrothermalvergasung”, promotional reference 03SF0350A, in the “Bio-Energie 2021” program. Project partners Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany | Karlsruhe Institute of Technology (KIT), Germany | Paul Scherrer Institute PSI, Villigen, Switzerland | Daimler AG, Stuttgart, Germany | EnBW Energie Baden- Württemberg AG, Karlsruhe | FairEnergie GmbH, Reutlingen, Germany | Netzsch Mohnopumpen GmbH, Selb, Germany | Stulz Wasser- und Prozesstechnik GmbH, Grafenhausen, Ger- many | Subitec GmbH, Stuttgart, Germany | City of Stuttgart, Stuttgart, Germany fruit and vegetable waste digestion in 180 liter FPA reactors over a four month period. The ammonium concentration of approximately 800 mg/L contained in the liquid digestate was fully depleted. The biomass concentration in the FPA reactor was 2.5 g/L to 5.5 g/L between the times of harvest. The volumetric biomass productivity fluctuated between and 0.35 g L–1 d–1 depending on the weather conditions. Outlook or the first time, digestion of fruit and vegetable waste in changing composition could be carried out in a long-term operation under continuous conditions with a retention time of 17 days and in a stable manner with high degradation level and high biogas yield. The material cycles were closed by utilization of the biogas (not shown) and utilization of the digestate. The use of liquid digestate as a medium component for algae cultivation is one step towards decreased production costs for algal biomass. But the results also show a way to reduce the nitrogen and phosphate loads of liquid digestate and to produce phototrophic biomasses that can be used for material and energy recovery. This result is linked to a reduc- tion of costs in both algae production and in wastewater treatment of biogas processes. 1 Fruit and vegetable waste from the Stuttgart wholesale market. 2 Two-stage pilot plant for the digestion of fruit and vegetable waste. 3 Greenhouse facility with 180 liter flat- panel airlift reactors. 4 Procedure and value-added chain. 4 products/ semifinished goods milling hydrothermal gasification phase separation digestate solid digestate two-step algae cultivation light biowaste algae residues, expired fruits and vegetable waste two-step diges- tion process inert residues liquid digestate (nutrients) algal oil biogas CO2 methane gas tank biogas upgrading gas station Phone +49711970-4128 Phone +49711970-4111