Carbohydrate-to-protein ratio regulates hydrolysis and acidogenesis processes during volatile fatty acids production

In this study, the typical model solubilized and hydrolyzed substrates of protein and carbohydrate were anaerobically fermented at different carbohydrate-to-protein (Car/Pro) ratios to examine volatile fatty acids (VFAs) production and substrate consumption. The highest VFAs yields of 0.71 and 0.72 mg COD/mg CODsubstrate both occurred at Car/Pro ratio of 1 by BSA-dextran and amino acids (AAs)-glucose fermentation, respectively. The limiting processes were hydrolysis and acidogenesis for the higher Car/Pro ratio of 3 and lower Car/Pro ratio of 0.25, respectively. An inhibitory effect of AAs accumulation was found, and VFAs production could be raised by 25.5% through quartic fed-batch strategy. There existed a significant relationship between activity of hydrolytic and acid-forming enzymes and acidogenic metabolism efficiency, which could be fitted by first-order kinetic and Logistic-based models. Understanding the effects of Car/Pro ratio on VFAs production is of guiding significance for regulating hydrolysis and acidogenesis processes during anaerobic fermentation of organic wastes.

Automated summary

This study investigated the production of volatile fatty acids (VFAs) and substrate consumption in anaerobic fermentation under different carbohydrate-to-protein (Car/Pro) ratios. The highest VFAs yields were observed at a Car/Pro ratio of 1 for BSA-dextran and amino acids-glucose fermentation. Hydrolysis and acidogenesis were identified as the limiting processes for higher and lower Car/Pro ratios, respectively. Accumulation of amino acids was found to have an inhibitory effect, but VFAs production could be increased by 25.5% through quartic fed-batch strategy. The activity of hydrolytic and acid-forming enzymes was significantly related to the efficiency of acidogenic metabolism.