Production of biogas from different organic materials is a most interesting source of renewable energy.The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.

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Process water reuse was exercised in the hydrothermal carbonization (HTC) of paper at 200 °C for 16 h, four times. Results showed that hydrochar mass yields increased significantly in the first recirculation step but only slightly in further steps. At the same time, solid carbon content did not increase, and a constant organic carbon distribution between the three product streams, hydrochar, process water (PW), and gas phase, was observed over all recycling steps. Dissolved organic carbon content (DOC) and chemical oxygen demand (COD) of the PWs increased, as well as total acids content, among those specifically lactic, acetic, formic, and propionic acid. Surprisingly, the aerobic biodegradability of the PWs decreased as indicated by lower biochemical to chemical oxygen demand (BOD/COD) ratios in reused process waters. Subsequent methanogenesis of the PW revealed that a high amount of biogas was produced; however, no increase was seen with each recirculation step.

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Microbiome based anaerobic digestion combined with microbial electrochemical technologies exploits biomass efficiently and flexibly by concurrent conversion to methane and electrons.

Background: Waterweeds (Elodea nuttallii and Elodea canadensis) are invasive neophytes, which have been proliferating at a phenomenal rate during the last decades in German waterways. In case of overgrowth, the strong covering of vegetation can cause problems in hydroelectric power plants and leads to limitations in ship and boat traffic as well as in use for bathing and fishing activities. After vegetation period, dead plants can accumulate and then negatively influence flood protection and water engineering works. For this reason, the aquatic biomass has been periodically removed and disposed without further use. In order to enable the energetic use of this water-containing substrate, the aim of the present study was the optimization of storage methods for an aquatic plant-based feedstock for biogas production. In climatic cold regions, substrate conservation is necessary in order to guarantee a year-round substrate availability. With waterweed (Elodea) taken as an example, the ensiling of aquatic plants was studied. The main focus was to develop practical methods for biomass conservation while producing high biogas yields. Methods: Elodea was harvested in the river Parthe in Leipzig-Schönefeld in October 2015. Silage mixtures of Elodea and wheat straw were tested after 180 days of storage for pH, volatile fermentation products, and methane potentials. The effect of different silage moisture contents and straw particle sizes on the substrate quality was studied. Results: Results show that waterweeds can be stored by ensiling and can achieve considerable biogas yields. However, with a water content of about 95%, the storability of the material is challenging. Mixed silage of waterweeds and wheat straw were suitable for storage in clamp silos. The pH values were between 4.9 and 6.5, and the volatile fatty acid content as lactic acid ranged from 0.0 to 1.9% total solid. The mixed silages achieved methane potentials between 166 and 228 mL g − 1 volatile solid (VS), which is equivalent to 52 and 72% of maize silage. Considering a methane potential of 228 mL g − 1 VS and costs for material pretreatment, the most promising silage variant was mixed silage from waterweeds and ground straw with 30% total solid content. Conclusions: Long storability of waterweeds could be possible by ensiling fermentation. Mixed silages from Elodea and wheat straw show suitable substrate characteristics for biogas production and can achieve high biogas yields.

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