Impacts of medium composition and applied current on recovery of volatile fatty acids during coupling of electrodialysis with an anaerobic digester

Abstract

The accumulation of volatile fatty acids (VFAs) lowers anaerobic digestion (AD) performance. In this study, electrodialysis (ED) was coupled with AD to remove VFAs. The results show that acetate and propionate were removed once the current was applied during ED even in the presence of medium. However, current efficiency was <70%. Energy consumption was higher under a lower VFA concentration, and the maximum value reached 46.0 kW h/kg-acetate. Ethanol diffusion was not detected during laboratory-scale ED. The acetate removal percentage was about 40% in the ED-AD system, which was much faster than that of AD. However, the applied current significantly reduced bacterial activity, and no methane production was detected during the 50 days after the ED experiment. Therefore, separating the anaerobes from the fermentation broth before ED is necessary to maintain bacterial activity during AD.