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Baker's Yeast Industry (BYI) effluent was one of the strongest wastewaster type that contains high amount of organic matter, salinity, nitrogen and sulphate. These characteristics were unfavorable for the application of wastewater treatment. For this reason, a recovery-oriented approach was applied for the appropriate conditions to increase the Volatile Fatty Acid (VFA) production potential of BYI. In this concept, hydrolysis anaerobic Membrane Bioreactor was used to produce VFAs. The hydrolysis reactor was operated between 2.5 and 13.4 days in Hydraulic Retention Time, at a thermophilic temperature (55 °C) and at pH of 4.5–8 for 858 days. The highest biomass concentration was 26 g L−1 in the reactor, and mainly acetate, propionate and butrate production was observed. The highest acetate production was seen at pH 7 with an average concentration of 25,930 mg L−1. The highest total VFA production yield was 0.98 g VFA–COD g−1 COD. It was concluded that carrying out hydrolysis and acidification reactions at neutral pH was better as long as methane production could be avoided. In addition, a VFA-rich stream with free suspended solids could be obtained with the 0.05 µ pore diameter submerged membrane. Population dynamics remained quite stable and rich in biomass consortia throughout the study. It was suggested that a high commercial value could be obtained, especially by recovering acetate from the hydrolysis reactor's outlet stream. [ABSTRACT FROM AUTHOR]

The valorisation of protein-rich residual streams by anaerobic mixed-culture fermentation (MCF) has been barely studied in contrast to carbohydrate-rich wastes. The aim of this work was, therefore, to investigate how protein composition, i.e. the amino acid (AA) profile, affects the individual consumption of amino acids and, consequently, the outcome of the process. Mixed-culture fermentations were performed with two model proteins (casein and gelatin) using continuous and batch reactors at neutral pH values and 25 °C. The acidification was incomplete for both proteins, with casein achieving a higher value than gelatin. Albeit dominated by acetic acid, product spectra were different as well, with n-butyric acid as the second major product for casein and propionic acid for gelatin. The preferential consumption of amino acids was demonstrated, which interestingly depends on protein composition. The previously accepted stoichiometry accurately describes iso and n-butyric acid production, but it fails for propionic, iso and n-valeric acid generation. Overall, this study offers a better understanding of protein fermentation mechanisms, which will help to improve degradation models and to design fermentation processes, based on optimal substrate selection. Image 1 • Protein fermentation generally results in incomplete acidification. • Balanced amino acid redox roles do not guarantee higher acidification degrees. • The preferential consumption of amino acids was demonstrated. • Protein composition affects acidification, selectivity and preferential consumption. • The accepted stoichiometry is not sufficient to describe protein conversion to VFA. [ABSTRACT FROM AUTHOR]