Many cyanobacteria produce extracellular polymeric substances (EPS) mainly composed of heteropolysaccharides with unique characteristics that make them suitable for biotechnological applications. However, manipulation/optimization of EPS biosynthesis/characteristics is hindered by a poor understanding of the production pathways and the differences between bacterial species. In this work, genes putatively related to different pathways of cyanobacterial EPS polymerization, assembly, and export were targeted for deletion or truncation in the unicellular Synechocystis sp. PCC 6803. No evident phenotypic changes were observed for some mutants in genes occurring in multiple copies in Synechocystis genome, namely ∆wzy (∆sll0737), ∆wzx (∆sll5049), ∆kpsM (∆slr2107), and ∆kpsM∆wzy (∆slr2107∆sll0737), strongly suggesting functional redundancy. In contrast, Δwzc (Δsll0923) and Δwzb (Δslr0328) influenced both the amount and composition of the EPS, establishing that Wzc participates in the production of capsular (CPS) and released (RPS) polysaccharides, and Wzb affects RPS production. The structure of Wzb was solved (2.28 Å), revealing structural differences relative to other phosphatases involved in EPS production and suggesting a different substrate recognition mechanism. In addition, Wzc showed the ATPase and autokinase activities typical of bacterial tyrosine kinases. Most importantly, Wzb was able to dephosphorylate Wzc in vitro, suggesting that tyrosine phosphorylation/dephosphorylation plays a role in cyanobacterial EPS production.

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The present paper aims at assessing the carbon and energy footprint of an innovative process for carbon dioxide recycling, with flue gas as feedstock of nitrogen and carbon dioxide. Nitrogen is converted into ammonia through the Haber-Bosch process and carbon dioxide into methane via Sabatier reaction using hydrogen produced by renewable electricity excess. Carbon and energy footprint analysis of the process was assessed based on experimental data related to hydrogen production by electrolysis, methane synthesis via Sabatier reaction, energy consumption and energy output of the process units for flue gas separation, carbon dioxide methanation and ammonia synthesis. A Life Cycle Assessment method is applied, based on the experimental and computational data, both in case of renewable electricity excess and electricity from the grid. Results show that in case of renewable electricity excess, for a functional unit of 1 kg of treated flue gas, the specific carbon footprint is 0.7819 kgCO2eq and energy footprint is 50.73 MJ, which correspond to 4.012 kg and 260.3 MJ per 1 kg of produced hydrogen. In case of electricity from the grid, the specific carbon footprint is 1.550 kgCO2eq and energy footprint is 59.12 MJ per flue gas mass unit. If the carbon footprint is positive, the process indirectly leads to avoided emissions, ranging from 0.673 to 0.844 kgCO2eq kg−1fluegas, thus proving the sustainability of the proposed pathway.@en

In EU where the architectural heritage is significant, enhancing the energy performance of historical buildings is of great interest. Constraints, such as the lack of space especially within the historical centers and architectural peculiarities, make the application of technologies for renewable energy production and storage a challenging issue. This study presents a prototype system consisting in using the renewable energy from a Photovoltaics (PV) array to compress air for a later expansion to produce electricity when needed. The PV-integrated small scale Compressed Air Energy Storage system is designed to address the architectural constraints. It is located at the unoccupied basement of the building. An energy analysis was carried out for assessing the performance of the proposed system. The novelty of this study is to introduce experimental data of a CAES prototype suitable for dwelling application as well as its integration accounting for architectural constraints. The simulation, carried out for a summer average day, shows that the compression phase absorbs 32 % of PV energy excess in a vessel of 1.7 m3 and the expansion phase covers 21.9 % of the dwelling energy demand. The electrical efficiency of a daily cycle is equal to 11.6 %. If air is compressed at 225 bar, instead of 30 bar, 96.0 % of PV energy excess is stored in a volume of 0.25 m3, with a production of 1.273 kWh, 26.0 % of the demand.@en

The utilization of the captured CO2 as a carbon source for the production of energy storage media offers a technological solution for overcoming crucial issues in current energy systems. Solar energy production generally does not match with energy demand because of its intermittent and non-programmable nature, entailing the adoption of storage technologies. Hydrogen constitutes a chemical storage for renewable electricity if it is produced by water electrolysis and is also the key reactant for CO2 methanation (Sabatier reaction). The utilization of CO2 as a feedstock for producing methane contributes to alleviate global climate changes and sequestration related problems. The produced methane is a carbon neutral gas that fits into existing infrastructure and allows issues related to the aforementioned intermittency and non-programmability of solar energy to be overcome. In this paper, an experimental apparatus, composed of an electrolyzer and a tubular fixed bed reactor, is built and used to produce methane via Sabatier reaction. The objective of the experimental campaign is the evaluation of the process performance and a comparison with other CO2 valorization paths such as methanol production. The investigated pressure range was 2–20 bar, obtaining a methane volume fraction in outlet gaseous mixture of 64.75% at 8 bar and 97.24% at 20 bar, with conversion efficiencies of, respectively, 84.64% and 99.06%. The methanol and methane processes were compared on the basis of an energy parameter defined as the spent energy/stored energy. It is higher for the methanol process (0.45), with respect to the methane production process (0.41–0.43), which has a higher energy storage capability.@en