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La mise en place et le développement de la méthanisation sont intrinsèquement liés à des questions géographiques et aux prises de position des institutions. Il est intéressant d’observer comment cela s’opère en Italie, de voir où les priorités sont placées et quels choix sont fait, notamment ici dans la région de Vénétie.

One of the objectives of the European Union (EU) 2030 strategy is the sustainable growth through a series of measures focused on the application of the “Circular Economy” (ec.europa.eu, 2020) with many benefits also for climate, environment, and society. Food waste and sewage sludge management is part of this actions plan. Both streams are ideal source for microbial valorization processes to produce biofuels in a sustainable way. Anaerobic digestion (AD) is the benchmark robust technology for biogas production; however, the dark fermentation (DF) is a higher-rate process which offers the possibility to accumulate important building blocks (volatile fatty acids; VFA) and hydrogen from renewable resources, at reduced volumetric impact compared to AD. Focusing on this goal, the effectiveness of the hydrogenase enzymes needs to be favoured; some strategies have been already adopted: maintaining pH between 5.0-6.0; limiting the activities of methanogenic bacteria, not responsible for VFA and H2 accumulation, by decreasing the hydraulic retention time (HRT). Mesophilic and thermophilic bio-H2 and VFA production by DF process from food waste (alone or mixed with sewage sludge) has been studied in this work through batch assays. Pursuing the interest of studying interactions between adsorbents materials and bacteria, some trials were amended with zeolite (Z; chabazite type) at zeolite/inoculum ratio (Z/I) of 0.20 g Z/g VSinoculum. The zeolite’s presence brought the H2 yield up to 0.04 m³ H2/kg VS in thermophilic trials, in parallel to the increased acetic acid production (close to 50% of the organic acids, including lactic and VFA). The rate of H2 production also increased with Z addition, up to 27.3 mmol/(L d), 23% higher than control without Z. The positive effect of zeolite could be related to its associated surface area (available for bacterial adhesion), or ability to adsorb/exchange protons. These results open novel perspectives not only in bio-H2 production but also in the study of interactions between bacteria and inorganicporous materials. [ABSTRACT FROM AUTHOR]

Summary: High‐temperature bioconversion of lignocellulose into fermentable sugars has drawn attention for efficient production of renewable chemicals and biofuels, because competing microbial activities are inhibited at elevated temperatures and thermostable cell wall degrading enzymes are superior to mesophilic enzymes. Here, we report on the development of a platform to produce four different thermostable cell wall degrading enzymes in the chloroplast of Chlamydomonas reinhardtii. The enzyme blend was composed of the cellobiohydrolase CBM3GH5 from C. saccharolyticus, the β‐glucosidase celB from P. furiosus, the endoglucanase B and the endoxylanase XynA from T. neapolitana. In addition, transplastomic microalgae were engineered for the expression of phosphite dehydrogenase D from Pseudomonas stutzeri, allowing for growth in non‐axenic media by selective phosphite nutrition. The cellulolytic blend composed of the glycoside hydrolase (GH) domain GH12/GH5/GH1 allowed the conversion of alkaline‐treated lignocellulose into glucose with efficiencies ranging from 14% to 17% upon 48h of reaction and an enzyme loading of 0.05% (w/w). Hydrolysates from treated cellulosic materials with extracts of transgenic microalgae boosted both the biogas production by methanogenic bacteria and the mixotrophic growth of the oleaginous microalga Chlorella vulgaris. Notably, microalgal treatment suppressed the detrimental effect of inhibitory by‐products released from the alkaline treatment of biomass, thus allowing for efficient assimilation of lignocellulose‐derived sugars by C. vulgaris under mixotrophic growth. [ABSTRACT FROM AUTHOR]

In recent years, the attention to organic wastes as a new feedstock for the production of PHA is increased based on the idea that this is the only way to reduce their high cost and to increase their sustainability. For this reason, a pilot platform has been designed to produce PHA from the source-sorted organic fraction of municipal solid waste (OFMSW). The cost-effective system consists in the three-steps anaerobic-aerobic process: the fermentation step was performed in a 200 L CSTR (OLR 20.0 kgVS/m³.d, HRT 3.3 d) in thermophilic conditions (55°C). The VFA-rich mixture was used for the two following aerobic steps: a first sequencing batch reactor (SBR, 100 L) for the production of functionalized PHA-producing biomass (mixed consortium, MMC), and a second batch reactor (50 L) for production of PHA and its maximization inside cell walls. The SBR was operated at 1.2-2.5 kgCOD/m³.d as OLR, and HRT of 1 d (equal to SRT); dynamic feeding regime (feast-famine) was used for consortium selection. The fermentation conditions allowed obtaining a significant COD conversion into VFA. Acetic, propionic and butyric acids accounted for more than 80% of total VFA and the relative yield was 0.45 ± 0.03 CODVFA/VS. The necessary buffering capacity was provided by anaerobic digestate addition, which increased the system alkalinity (2.8 ± 0.2 gCaCO3/L at pH 5.75). In SBR, a strong selective pressure favouring PHA-accumulating organisms was easily reached, as demonstrated by the short feast-to-cycle length ratio (often below 0.12). In the second aerobic accumulation reactor, the biomass was able to accumulate up to 49% gPHA/gVSS. Both aerobic steps were performed without temperature (T) control, avoiding additional consumption of energy; the applied OLR was chosen based on biomass kinetic in order to have a constantly short feast phase and a stable selection/enrichment of PHA-accumulating consortium. [ABSTRACT FROM AUTHOR]