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The inhibition of coq2 by 4‐nitrobenzoate decreases the CoQ content, promoting the biosynthesis of cholesterol. The increased cholesterol content reduces the plasma membrane fluidity, lowering intracellular oxygen tension. The OxPhos activity and the antioxidant defences are decreased. These conditions favor the stabilization of hypoxia‐inducible factor 1α, which mediates the adaptive metabolic response stimulating the glycolytic pathway, with enhanced glucose entry and induction of the PMOR system to lessening the intracellular reducing power.

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A transdisciplinary approach that integrates thermochemical conversions and biological transformations for valorizing C-content and chemical energy of anaerobically digested sewage sludge and producing biopolymers (polyhydroxyalkanoates, PHA) and drop-in chemicals (crotonic acid) has been presented here. Hydrothermal carbonization has increased by 10-times the soluble COD of sewage sludge, allowing it to split 44–54% of its COD into an aqueous phase (HTCap) enriched in small fermentable organic molecules; the coupling of acidogenic fermentation and aerobic fermentation converted these substrates first into volatile fatty acids (20% of CODHTCap) and then into PHA (about 20% of CODVFA). The extraction of microbial biomass with dimethyl carbonate (DMC) allowed high quality PHA to be produced, with a high molecular weight (0.9 MDa) and a percentage of medium chain monomers (hydroxyvalerate and hydrohexanoate) close to 12%. The postextraction microbial biomass, still containing a relevant portion of “unextractable” PHA, was last treated at 300 °C to selectively convert the PHA-backbone into crotonic acid with a 42% yield on PHA content basis.

Polyhydroxyalkanoates (PHA) are a key constituent of excess sludge produced by Aerobic Sewage Sludge Treatment plants. The accumulation of significant amount of PHA inside aerobic microbial cells occurs when a surplus of an easily degradable carbon source (e.g., volatile fatty acids, VFA) is found in combination with other nutrients limitation. Herein, hydrothermal treatment (HT) of PHA-containing sludge at 300 and 375 °C was demonstrated to be effective in converting most (>70% w/w) of the bacterial PHA stored inside microbial cells into alkene/CO gas mixtures. Simultaneously, most of non-PHA biomass was converted into water-soluble compounds (50% carbon yield) that were acidogenic fermented to produce volatile fatty acids, ideal substrate to feed aerobic bacteria and produce more PHA. According to results here presented, HT of excess sludge with moderate (13%) PHA content can produce about 50 kg of alkenes per tonne of suspended solids treated, with a significant reduction of sludge mass (80% reduction of wet sludge volume) and consequent disposal cost.