Microbial protein (MP) can alleviate the increasing pressure of food demand on agriculture and our environment. For its sustainable production, feedstocks such as biomethane or (bio)hydrogen are needed. Here, we coupled biogas produced from agricultural waste directly with electrochemical biogas upgrading to subsequently produce MP from methane, hydrogen or a mixture thereof. Biogas was produced from co-digestion of pumpkin and pig manure at production rates of 0.73 ± 0.24 Lbiogas L -1 reactor day -1 (59 % CH4) and 0.59 ± 0.29 Lbiogas L -1 reactor day -1 (50% CH4). The biogas was directed to the cathode of an electrochemical cell. At current densities of 20 and 40 A m −2 , CO2 removal efficiencies of 88 ± 14 % and 99 ± 1 % were achieved. Enrichments of MP (hydrogen-and methane oxidizing bacterial cultures)were cultivated on either raw biogas or gases obtained from the cathode (CH4, CO2, H2) and anode (CO2, O2) in batch mode with external supplementation of O2 and H2 when required.The best performance was obtained when the cathode off-gas was used in terms of biomass concentration (0.585 g CDW L -1 ), yield (0.150 g CDW g -1 COD), efficiency of COD conversion to protein (17%) volumetric biomass productivity (0.226 g CDW L -1 day -1 ) and volumetric protein productivity (0.181 g protein L -1 day -1 ). The protein content was similar when using anode and cathode off-gases (66.3 ± 7.3 % of CDW) with raw biogas resulting in a 6 % lower protein content. This proof of concept demonstrated that electrochemical biogas upgrading enables steering MP production.

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The production of biogenic palladium nanoparticles (bio-Pd NPs) is widely studied due to their high catalytic activity, which depends on the size of nanoparticles (NPs). Smaller NPs (here defined as <100 nm) are more efficient due to their higher surface/volume ratio. In this work, inductively coupled plasma-mass spectrometry (ICP-MS), flow cytometry (FCM) and transmission electron microscopy (TEM) were combined to obtain insight into the formation of these bio-Pd NPs. The precipitation of bio-Pd NPs was evaluated on a cell-per-cell basis using single-cell ICP-MS (SC-ICP-MS) combined with TEM images to assess how homogenously the particles were distributed over the cells. The results provided by SC-ICP-MS were consistent with those provided by "bulk" ICP-MS analysis and FCM. It was observed that heterogeneity in the distribution of palladium over an entire cell population is strongly dependent on the Pd 2+ concentration, biomass and partial H 2 pressure. The latter three parameters affected the particle size, ranging from 15.6 to 560 nm, and exerted a significant impact on the production of the bio-Pd NPs. The TEM combined with SC-ICP-MS revealed that the mass distribution for bacteria with high Pd content (144 fg Pd cell −1 ) indicated the presence of a large number of very small NPs (D50 = 15.6 nm). These results were obtained at high cell density (1 × 10 5 ± 3 × 10 4 cells μl −1 ) and H 2 partial pressure (180 ml H 2 ). In contrast, very large particles (D50 = 560 nm) were observed at low cell density (3 × 10 4 ± 10 × 10 2 cells μl −1 ) and H 2 partial pressure (10-100 ml H 2 ).The influence of the H 2 partial pressure on the nanoparticle size and the possibility of size-tuned nanoparticles are presented.