Hyperthermophilic fermentation as pre-treatment step in Biogas plants

HYPERFERMENTAN is carried out by the partners Hyperthermics AS (Project Owner), Hyperthermics Regensburg GmbH, NIBIO and NMBU. In parallel with the project, project owner has installed and put into operation a full-scale pilot plant with annual capacity of 10,000 tonnes. The two parallel projects are part of an overall strategy for commercializing hyperthermophilic fermentation as an effective biomass pre-treatment for increased and profitable biogas production. Hyperthermophilic pretreatment in a biogas process has the potential to: 1. Higher energy yield from biomass (waste) 2. Reduced external thermal energy due to internally generated free energy 3. Reduced operating costs due to reduced volume of residual biomass and higher solids concentration in biogas reactor 4. Reduced investment costs for plants due to higher load capacity or lower plant footprints. HYPERFERMETAN has, in addition to the direct project results, contributed to the establishment of laboratories and expertise for hyperthermophilic processes at the biogas laboratory at NIBIO / NMBU, collaboration with the Hyperthermics laboratory in Regensburg / University of Regensburg and competence transfer. The project partners will use the established infrastructure and expertise in further projects. The project has identified the best suitable hyperthermophilic organisms and optimal conditions in a bioreactor. A continuous bioreactor system consisting of a hyperthetmophilic reactor and a biogas reactor has been established as well as a theoretical model of the Hyperthermics process including kinetics, stoichiometry and calorimetry. The project has shown that pressurized liquid from source-sorted food waste works well as substrate for hyperthermophilic fermentation in continuous single cell culture. The project has had challenges in establishing continuous fermentation on a small scale due to inhomogeneity and solids in food waste. Part of the work in the laboratories has therefore been carried out on substrates that can be used on a small scale. Together with data from the pilot plant, it has been shown that the Hyperthermics process is robust and has good capacity to transform and optimize food waste into an easily accessible substrate for conversion into a subsequent biogas process. We have found that established bacterial culture reacts immediately to the supply of food waste in high concentrations (typically 10% solids). Laboratory trials have shown stable operation of continuous cultures of selected strains of Thermotoga on media based on glucose, starch or whey. Gas quantities, gas quality and estimates of cell densities are analyzed. The hyperthermophilic organisms short generation times are demonstrated and substantiate the hypothesis of utilizing dense bacterial cultures to generate exothermic heat. Optimization of substrate design through combinations of waste streams or the supply of external cheap carbohydrate sources enables increased economy and sustainability through lower demand for added heat or higher hydrogen and gas yields. Hydrogen from the process can be used in the biogas process to increase methane content. The potential of substrate design is important since energy-efficient waste fractions such as food waste are unstable and are rapidly fermented. This directly reduces the amount of carbohydrates and protein available for gas production.

HYPERFERMENTAN aims to demonstrate, in lab scale, secure hygienisation and substantial improvement of biogas yields through a hyperthermophilic (HT) fermentation step as an alternative to existing pasteurization, thermal hydrolyzing process (THP), or complicated operating regimes at thermophilic conditions. The integration of a hyperthermophilic pre-treatment revolutions the biogas industry by: 1. Higher energy yields from the chosen substrate (waste stream), 2. Less demands for external thermal energy input due to the generation of internal free energy from HT fermentations, 3. Less operational costs due to less surplus biosolid to handle, reduction in energy input, operating with higher dry solids concentration in the biogas reactor (DS), 4. Less investment costs due to higher loading capacities or lower foot prints, and 5. upgrading of biogas through exploitation of internal hydrogen production. The project will screen for best suitable hyperthermophilic strains, optimize the culture conditions for highest turnover rates, establish a continuous bioreactor system consisting of an HT and a biogas reactor, and build up a theoretical model of the HT process including kinetic, stoichiometric, and calorimetric aspects.