Nitrogen‐doped carbons were synthesized by a solvent‐free mechanochemically induced one‐pot synthesis by using renewable biomass waste. Three solid materials are used: sawdust as a carbon source, urea and/or melamine as a nitrogen source, and potassium carbonate as an activation agent. The resulting nitrogen‐doped porous carbons offer a very high specific surface area of up to 3000 m2 g−1 and a large pore volume up to 2 cm3 g−1. Also, a high nitrogen content of 4 wt % (urea only) up to 12 wt % (melamine only) is generated, depending on the nitrogen and carbon sources. The mechanochemical reaction and the impact of different wood components on the porosity and surface functionalities are investigated by nitrogen physisorption and high‐resolution X‐ray photoelectron spectroscopy (XPS). These N‐doped carbons are highly suitable as cathode materials for Li–S batteries, showing high initial discharge capacities of up to 1300 mAh gsulfur−1 (95 % coulombic efficiency) and >75 % capacity retention within the first 50 cycles at low electrolyte volume.

We developed an upcycling process of polyurethane obtaining porous nitrogen-doped carbon materials that were applied in supercapacitor electrodes. In detail, a mechanochemical solvent-free one-pot synthesis is used and combined with a thermal treatment. Polyurethane is an ideal precursor already containing nitrogen in its backbone, yielding nitrogen-doped porous carbon materials with N content values of 1–8 wt %, high specific surface area values of up to 2150 m2·g−1 (at a N content of 1.6 wt %) and large pore volume values of up to 0.9 cm3·g−1. The materials were tested as electrodes for supercapacitors in aqueous 1 M Li2SO4 electrolyte (100 F·g−1), organic 1 M TEA-BF4 (ACN, 83 F·g−1) and EMIM-BF4 (70 F·g−1).

A demonstrator plant of a recently patented process for improved sludge degradation has been implemented on a municipal scale. In a 1500 m3 sewage sludge digester, an intermediary stage with aerobic sewage sludge reactivation was implemented. This oxic activation increased the biogas yield by up to 55% with a 25% reduction of the remaining fermentation residue volume. Furthermore, this process allowed an NH4-N removal of over 90%. Additionally, 16S rRNA gene amplicon high-throughput sequencing of the reactivated digestate showed a reduced number of methane-forming archaea compared to the main digester. Multiple ammonium-oxidizing bacteria were detected. This includes multiple genera belonging to the family Chitinophagaceae (the highest values reached 18.8% of the DNA sequences) as well as a small amount of the genus Candidatus nitrosoglobus (<0.3%). In summary, the process described here provides an economically viable method to eliminate nitrogen from sewage sludge while achieving higher biogas yields and fewer potential pathogens in the residuals.

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