Fig. 4b showed that the SCFAs composition in co-digestion of FW
and AS was changed by FW/AS. The content of the SCFAs was as
follows: acetic acid > propionic acid > iso-valeric acid > iso-butyric
acid > n-butyric acid > n-valeric acid. The acetic acid and proponic
acid were the main SCFAs in all reactors. The percentage of proponic acid at FW/AS of 30% was more than that at other FW/AS,while the percentage of acetic acid was lower than other samples,
since acetic acid was easily converted to biogas in AD process (Jang
et al., 2013). According to the above results, FW/AS changed the
transformation of SCFAs, just as acetic acid, which further caused
the change of SCFAs composition.