Complex I and alternative NADH dehydrogenase (NDH-2)

The work presented in this Thesis addressed the diversity of respiratory membrane enzymes with special focus on type I and type II NADH:quinone oxidoreductases. The searching for common denominators that characterize these enzymes in order to find minimal functional elements relevant for their operation was the main rational in this work.(...

Donnan Dialysis for Recovering Ammonium from Fermentation Solutions Rich in Volatile Fatty Acids

Funding Information: Universitat Politècnica de València and Ministerio de Universidades de España (Plan de Recuperación, Transformación y Resiliencia—financed by European Union—Next GenerationEU) are acknowledged for the post-doctoral research grant attributed to Kayo Santana Barros. Funding Information: This work was financed by Fundação para a Ciência e a Tecnologia, I.P., Lisbon, Portugal in the scope of the projects UIDP/04378/2020, UIDB/04378/2020 and PTDC/BTA-BTA/30902/2017 of the Research Unit on Applied Molecular Biosciences—UCIBIO and the project LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy—i4HB. The work was also supported through the projects UIDB/50006/2020 and UIDP/50006/2020, funded by FCT/MCTES through national funds. Publisher Copyright: © 2023 by the authors.For the production of polyhydroxyalkanoates (PHA) using nitrogen-rich feedstocks (e.g., protein-rich resources), the typical strategy of restricting cell growth as a means to enhance overall PHA productivity by nitrogen limitation is not applicable. In this case, a possible alternative to remove the nitrogen excess (NH4+/NH3) is by applying membrane separation processes. In the present study, the use of Donnan dialysis to separate ammonium ions from volatile fatty acids present in the media for the production of PHA was evaluated. Synthetic and real feed solutions were used, applying NaCl and HCl receiver solutions separated by commercial cation-exchange membranes. For this specific purpose, Fumasep and Ralex membranes showed better performance than Ionsep. Sorption of ammonium ions occurred in the Ralex membrane, thus intensifying the ammonium extraction. The separation performances with NaCl and HCl as receiver solutions were similar, despite sorption occurring in the Ralex membrane more intensely in the presence of NaCl. Higher volumetric flow rates, NaCl receiver concentrations, and volume ratios of feed:receiver solutions enhanced the degree of ammonium recovery. The application of an external electric potential difference to the two-compartment system did not significantly enhance the rate of ammonium appearance in the receiver solution. The results obtained using a real ammonium-containing solution after fermentation of cheese whey showed that Donnan dialysis can be successfully applied for ammonium recovery from such solutions.publishersversionpublishe