Single- vs. two-stage fermentation of an organic fraction of municipal solid waste for an enhanced medium chain carboxylic acids production − The impact of different pH and temperature
Anna Duber, Roman Zagrodnik, Natalia Gutowska, Filip Brodowski, Tomasz Dąbrowski, Sławomir Dąbrowski, Mateusz Łężyk, Piotr Oleśkowicz-Popiel
Abstract
• OFMSW was valorised to MCCA at specificity of 40% and conversion efficiency of 23%. • Two-stage fermentation enabled almost twofold increase in caproate production. • The maximum caproate concentration reached 4.0 g/L (8.4 gCOD/L) and specificity of 37 %. • Number of reads annotated to FAB exceeded the number of reads assigned to RBO. • The core microbial community belonged to Clostridia, e.g. Caproiciproducens sp. Single-stage fermentation was characterized by low medium chain carboxylic acids concentrations and different mesophilic temperatures had little effect on the process performance, whereas thermophilic conditions and pH 5.5 led to lactate and ethanol accumulation. Two-stage fermentation enabled almost twofold increase in the caproate productivity, that reached 0.8 g/L-d (1.7 ± 0.1 gCOD/L-d) with a caproate concentration of 4.0 g/L (8.4 gCOD/L) at specificity of 37% and led to a reduced release of carbon dioxide. Under pH 6.5 and temperature of 37°C the production of medium chain carboxylic acids required higher concentrations of ethanol. Number of genes annotated to fatty acid biosynthesis pathway exceeded the number of sequences assigned to the reverse β-oxidation pathway. Core microorganisms encoding these pathways belonged to Caproiciproducens, Caproicibacterium and Clostridium . This study provides a valuable insight for valorisation of organic fraction of municipal solid waste into carboxylates in a single- and two-stage systems.