and detected at the highest concentrations of 9.2 and 6.7 g L1, respectively. However, under the neutral condition, produced ethanol and lactic acid were quickly consumed along with the accumulation of VFAs. Ethanol addition enhanced valeric acid and caproic acid production, while lactic acid addition enhanced propionic acid and butyric acid production. Further research is needed for a better understanding of longer chain VFAs
production regulated by addition of electron donors, such as the
role of lactic acid on chain elongation and the corresponding
microbial community succession.