110 / 2021-06-30 22:23:55

Kinetic effects of temperature on accumulation of volatile fatty acids during anaerobic digestion of food wastes, looking in the balance between production and degradation

Anaerobic digestion,Temperature,Volatile fatty acids,Food waste,Kinetics

    To reveal the effect of temperature on the accumulation of volatile fatty acids (VFAs), this study selected food waste (FW), various organic components and typical VFAs as substrates, to carry out a series of batch tests under mesophilic and thermophilic conditions, analyzed systematically the causes and characteristics on accumulation from the aspects of production and degradation of VFAs. The results showed that under thermophilic conditions, the main accumulative type of VFAs on the anaerobic digestion of FW was propionate. Specifically, among the four specific organic components of FW, protein had the highest conversion rates of propionate and valerate, reaching more than 13% and 8%, respectively, while which of others were  less than 9% and 3%; moreover, the thermophilic condition further promoted the production of VFAs, especially for the conversion process of protein to VFAs, the conversion rate increased by 13.9%. Compared with the mesophilic conditions, kinetic analysis of the maximum substrate utilization index (Km) of protein and lipid increased by 0.103 and 0.132 g COD/g VSS·d, respectively, which illustrated protein was the main factor for the obvious accumulation of VFAs under thermophilic conditions. And from the perspective of VFAs degradation, thermophilic condition promoted the degradation of acetate and butyrate but adversely inhibited the microbial activity of degrading propionate; and as the intermediate of valerate, the Km of propionate decreased from 0.090 to 0.079 g COD/g VSS·d, to further affected the Km of valerate even decreased by 0.013 g COD/g VSS·d. This became one of the main reasons for the plateau of valerate degradation. Furthermore, RDA analysis revealed that protein was the main component that affected the accumulation of VFAs. Under thermophilic conditions, the Km of protein (0.266 g COD/g VSS·d) was significantly higher than that of propionate (0.079 g COD/g VSS·d) and valerate (0.129 g COD/g VSS·d), while lower than that of acetate (0.330 g COD/g VSS·d) and butyrate (0.326 g COD/g VSS·d), which exacerbated the imbalance of production and degradation of propionate and valerate, making a more serious accumulation of VFAs.