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Background: Poly(3‐hydroxybutyrate) (PHB) is a polymer produced by Azotobacter vinelandii. The production of PHB in a bioreactor is affected by oxygen transfer conditions. The aim of this study was to evaluate PHB synthesis in extended batch of A. vinelandii, to obtain an operation curve (productivity versus oxygen transfer rate) and to scale up the bioprocess. Results: PHB production by A. vinelandii under dinitrogen fixation was evaluated using an extended batch modality under different oxygen transfer rates (OTRs). Extended batch cultures were performed using different agitation rates (400, 600, 800 and 1000 rpm), which determined different OTRs in the cultures. Under the conditions evaluated, it was possible to establish an operation curve of PHB productivity at different OTRs, allowing for the establishment of the maximum productivity of PHB. The maximum PHB productivity obtained was 0.40 ± 0.05 g L−1 h−1, which was reached under an OTR of 22.1 ± 1.5 mmol L−1 h−1. Using the OTR as a criterion to scale up PHB production from 3 to 30 L, it was possible to obtain a similar PHB concentration (7.9 ± 0.0 g L−1) and volumetric productivity (0.43 ± 0.04 g L−1 h−1) on a 30 L scale. Conclusions: The results lead to the conclusion that in extended cultures and under dinitrogen fixation in A. vinelandii cultures, the OTR value determines the maximum PHB productivity. This study provides evidence that the OTR is an adequate parameter as a criterion for the successful scaling up of PHB synthesis for the first time. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The updated Bioeconomy Strategy document "A sustainable bioeconomy for Europe: strengthening the connection between economy, society and the environment", which was issued by the European Commission in October 2018, encourages the exploitation of organic wastes according to a pyramidal hierarchy in which the extraction of valuable biomolecules, which will be used as they are or as precursors of high‐added‐value compounds, is a priority in biofuel production. This review considers a biorefinery platform in which food waste and sewage sludge are adopted to produce volatile fatty acids (VFAs) through a dark fermentation process. VFA fermentation is optimized by slightly acid pH (6–7), short hydraulic retention time (1–7 days) and high organic load rate (more than 10 gTS L−1 d−1). Attention has been focused on VFA exploitation for polyhydroxyalkanoate (PHA) production via a 'feast and famine' strategy performed in sequencing batch reactors. The obtained PHA yields are around 0.4–0.5 gPHA gCOD−1. Moreover, VFAs allow for the production of biofuels, such as hydrogen and methane, through single‐ or double‐staged anaerobic digestion. Innovative bioelectrochemical upgrade strategies for biogas helps producers to obtain biomethane for the automotive sector. Moreover, biogas has recently been tested for the production of polyhydroxybutyrate, a biodegradable and biocompatible thermoplastic made by microorganisms from C1 carbon sources (CO2 and CH4). Digestates from anaerobic bioreactors are still rich in nitrogen and phosphorus compounds. These latter compounds have been identified as critical raw materials due to their low availability in the European Union and to increasing demand from the growing global population. Thus, nutrient recovery from digestate allows users to close the loop of the 'circular economy' approach. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Rice husk, an agricultural waste, is abundantly available in many countries such as China, India, Brazil, US, and South East Asia. Despite the massive production of rice husk, it is mainly disposed to landfill. In this work, utilization of rice husk for a potential waste‐water treatment is evaluated, along with subsequent encapsulation of the adsorbed heavy metals (Pb and Cd) inside a porous glass‐ceramic. Vitrified bottom ash (another source of waste) was mixed with foaming agents in dif‐ ferent weight ratios (40:60, 50:50, and 60:40) to prepare a glass matrix for encapsulation of Pb‐/Cd‐loaded rice husk. It was shown that using 40 wt% vitrified bottom ash with 60 wt% foaming agents leads to a foam glass with the best pore size distribution. Therefore, this batch was further mixed with 70 volume% (5 wt%) heavy metal‐loaded rice husk and was heat‐treated at 750°C for 3 hours. The final glass‐ceramic porous structure was char acterized using SEM, XRD, compression test, and it was shown that it is safe to be used as it passes the EN12457‐2 leaching test. [ABSTRACT FROM AUTHOR]

In this work, ceria-based nanocatalysts mixed with copper and manganese were studied. All the catalysts were synthesized via the hydrothermal procedure. Four samples were prepared here denoted through the atomic ratios of the metals in the mixed oxide: Ce0.95Mn0.05, Ce0.95Cu0.05, Ce0.95Mn0.025Cu0.025 and CeO2. The samples were tested for the CO and soot oxidation reactions with different gas-phase oxygen concentrations (10, 1.0, 0.5 and 0.02 vol% O2). As a whole, the most promising catalysts for the CO oxidation reaction are the Ce0.95Cu0.05 and Ce0.95Mn0.025Cu0.025 samples. Indeed, the presence of Cu species in the solid enhances the surface redox mechanism for the CO oxidation. High vol% O2 values lead to competitive CO and O2 adsorption on the catalyst surface thus reducing the catalytic performances for binary and ternary oxides. On the other hand, the CO oxidation reaction over the CeO2 catalyst appears favored with 10 vol% O2. For the soot oxidation reaction, the most active catalyst (in terms of soot conversion %) is the CeO2 sample likely due to the unique feature of presenting well-defined and highly reactive nanocubic structures. Moreover, the presence of 10 vol% O2 in the mixture appears to be the best condition to oxidize the soot particles.Graphical Abstract: [ABSTRACT FROM AUTHOR]