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Cereal distillers grains, a by-product from bioethanol industry, proved to be a suitable feedstock for biogas production in laboratory scale anaerobic digesters. Five continuously stirred tank reactors were run under constant conditions and monitored for biogas production and composition along with other process parameters. Iron additives for sulfide precipitation significantly improved the process stability and efficiency, whereas aerobic pretreatment of the grains had no effect. The microbial communities in the reactors were investigated for their phylogenetic composition by terminal restriction fragment length polymorphism analysis and sequencing of 16S rRNA genes. The bacterial subcommunities were highly diverse, and their composition did not show any correlation with reactor performance. The dominant phylotypes were affiliated to the Bacteroidetes. The archaeal subcommunities were less diverse and correlated with the reactor performance. The well-performing reactors operated at lower organic loading rates and amended with iron chloride were dominated by aceticlastic methanogens of the genus Methanosaeta. The well-performing reactor operated at a high organic loading rate and supplemented with iron hydroxide was dominated by Methanosarcina ssp. The reactor without iron additives was characterized by propionate and acetate accumulation and high hydrogen sulfide content and was dominated by hydrogenotrophic methanogens of the genus Methanoculleus.

At urban locations certain challenges are concentrated: organic waste production, the need for waste treatment, energy demand, food demand, the need for circular economy and limited area for food production. Based on these factors the project presented here developed a novel technological approach for processing organic waste into new food. In this system, organic waste is converted into biogas and digester residue. The digester residue is being used successfully as a stand-alone fertilizer as well as main substrate component for vegetables and mushrooms for the first time - a "digeponics" system - in a closed new low energy greenhouse system with dynamic soap bubble insulation. Biogas production provides energy for the process and CO2 for the greenhouse. With very limited land use highly efficient resource recycling was established at pilot scale. In the research project it was proven that a low energy dynamic bubble insulated greenhouse can be operated continuously with 80% energy demand reduction compared to conventional greenhouses. Commercial crop yields were achieved based on fertilization with digestate; in individual cases they were even higher than the control yields of vegetables such as tomatoes, cucumber and lettuce among others. For the first time an efficient direct use of digestate as substrate and fertilizer has been developed and demonstrated.

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