Exploring the effects of substrate composition on acidogenic fermentation of carbohydrate-protein mixtures

The organic composition of the substrate is a pivotal factor that significantly influences the performance of acidogenic fermentation processes. Despite its importance, the impact of this parameter on acidification yields, effluent composition, and bacterial communities remains inadequately understood. This study presents a comprehensive and systematic analysis of acidogenic fermentation experiments, where the sole variable was the substrate's organic composition. Utilizing a sequencing batch reactor under consistent conditions (volumetric and specific organic loading rates, pH, and temperature), simulated wastewater substrates with varying proportions of soluble carbohydrates (C) and proteins (P): 100%P, 75%P/25%C, 50%P/50%C, 25%P/75%C, and 100%C was investigated. The results reveal that substrates comprising mixtures of carbohydrates and proteins achieve higher degrees of acidification, carboxylic acid production yields, and organic matter in the form of acids in the effluent compared to substrates solely composed of carbohydrates or proteins. Notably, an increased protein proportion in the influent correlates with reduced selectivity towards specific acids. It was possible to obtain linear correlations between the protein content in the substrate and the effluent composition of butyric, isobutyric, and isovaleric acids. Furthermore, the presence of different bacterial genera in the reactor were successfully linked to the effluent components corresponding to the various substrate compositions tested. This work sheds light about the critical role of substrate organic composition in acidogenic fermentation performance, providing valuable insights for optimizing acidogenic fermentation under controlled operational parameters.