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.