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2015|16 Annual Report Fraunhofer IGB

124 Bioenergy for mobility In order to reduce dependence on dwindling oil resources and increasing carbon dioxide emissions at the same time, the use of renewable energies represents a sustainable alternative. Here, the use of plant biomass for the production of bioener- gy – electricity, heat or fuel – plays a crucial role. Nevertheless, to date the potential of waste biomass to produce biogas as well as its use as fuel has been underexploited so far. Efficient biogas production from biomass Organic waste materials with very high proportion of water and low content of lignin and lignocellulose, for example waste from the food industry, wholesale market waste or algae residues, are perfectly suited for digestion. Coordinated by Fraunhofer IGB, a project consortium has thus set itself the objective to obtain maximum energy generation by completely converting easily digestable, low-lignocellulosic wet biomass into biogas using an adapted high-load digestion process and closing all material cycles at the same time. In the project EtaMax the consortium is focusing in particular on cost-effective biowaste and algal biomass, both of which present no competition to food production. Local production and utilization of renewable methane from biogas represent the core of the pro ect Purified biomethane was used as a fuel to power CNG (Compressed Natural Gas) vehicles. Liquid, nutrient-rich digestates accruing during digestion were used to cultivate microalgae, since the residues contain a sufficient quantity of inorganic nutrients required for the growth of algae. Conversion of wholesale market waste into biogas or the first time, e pired fruit and vegetable waste from a wholesale market tuttgart wholesale market was very effi- ciently converted into biogas using a two-stage process in two gas-lift reactors each with a capacity of 3.2 m3 . The high-load digestion process for this was developed at Fraunhofer IGB and has been technically realized for sewage sludge several times since 1994; the process was expanded and adapted for this substrate. With an adjusted hydraulic retention time of 17 days per stage, the system could also be run by changing fruit and veg- etable waste in a permanent and stable manner. Degradation levels of up to 95 percent could be reached with the largest part of degradation in stage 1. The biogas yield was between 840–920 norm liters of biogas per kilogram TVS (total volatile solids) added; the methane content was 55–60 percent. Biogas production and algae cultivation as an efficient material cycle For the energetic use of algal ingredients, Fraunhofer IGB de- veloped a two-stage, fully automated process for the outdoor production of lipid-rich algal biomass in flat-panel airlift reac- tors (FPA) and transferred the process to pilot scale. Closing the material cycles for nitrogen and phosphate between biogas production and algae cultivation was carried out using liquid digestate from biogas reactors as the medium component for the production of algal biomass. A mixed algae culture specifically adapted to this li uid digestate has been successfully cultivated with liquid digestate from the ETAMAX – BIOGAS FROM LOW-LIGNO- CELLULOSIC WASTE AND ALGAE RESIDUES Brigitte Kempter-Regel, Ulrike Schmid-Staiger, Steffen Görner, Alexander Laug, Stephan Scherle, Christian Bringmann, Lukas Röhrenbach, Ronja Münkel, Ursula Schließmann ENERGY 321