The effect of different C-N ratios on volatile fatty acid (VFAs) production from acidogenic fermentation of sucrose in continuous-stirred tank reactors

This study evaluates the production of volatile fatty acids (VFAs) from the acidogenic anaerobic digestion of sucrose in continuous-stirred tank reactors. A semi-continuously feed operational process was employed to observe the influence of different carbon-nitrogen ratios (C-N), from 5 to 100, on the volume and composition of VFA production. With a steady increase in VFA production, the C-N 5 assay attained the highest concentration with a VFA value of 26.08 g L-1 after 15 days of incubation, while on the 13th day of incubation, the maximum VFA concentration of 23.82 g L-1, 20.44 g L-1, 16.76 g L-1, 11.88 g L-1, and 11.60 g L-1 was attained in C-N 10, C-N 20, C-N 30, C-N 50, and C-N 70 assays respectively. Acetic acid and butyric acid were the principal VFAs observed in all the different C-N assays tested in this study. The mean values of acetic acid ranged from 64.58 to 79.12% for C-N increase between 5 and 100. On the other hand, C-N variations between 5 and 100 resulted in a significant decrease in butyric acid production from 30.33 to 13.93%. Volatile solid degradation and carbohydrate utilization rates decreased from 41.86 to 32.45% and 78.56 to 61.25% respectively as C-N ratios increased from 5 to 100. This aligns with the hypothesis that increasing the nitrogen content of substrate increases VFA production. Our findings provide new information regarding the C-N ratios for improved VFA production from acidogenic fermentation of sucrose.

Automated summary

This study evaluated the production of volatile fatty acids from the acidogenic anaerobic digestion of sucrose in continuous-stirred tank reactors. It found that increasing nitrogen content in the substrate led to higher VFA production, with acetic acid being the predominant VFA observed. The study highlighted the importance of carbon-nitrogen ratios in improving VFA production from acidogenic fermentation of sucrose.