Acidogenic fermentation of potato wastes to produce carboxylate platform chemicals : influence of cations used for pH control

Potato cropping and its industrial processing generate significant amounts of wastes/ residues which can be valorized for the sustainable production of value-added chemicals and energy (e.g. volatile fatty acids (VFAs) and biohydrogen) in biorefineries. These value-added products are produced through the acidogenic fermentation, which is a complex process influenced by several factors such as: temperature, pH, hydraulic retention time (HRT), organic loading rate, etc. In order to control the pH in semi-continuous bioreactors, we used three different carbonate salts (CaCO3, K2CO3 and Na2CO3), with the aim of assessing the potential inhibition effect of cations (Ca2+, K+, Na+) on the process while keeping the same anion (CO32-). Potato wastes were directly used with no physicochemical pretreatment and the acidogenic fermentation was monitored for 60 days under semi-continuous conditions. Maximum total VFA (tVFA) concentration was 24 g_COD/kg_mixed_liquor, and maximum yield of chemical oxygen demand (COD) conversion into tVFA was 42 % when the pH was neutralized by Na2CO3. Butyric, acetic and caproïc acid were the predominant VFA in all cases. The concentration of lactic acid was almost equal to caproïc acid concentration for the case of K2CO3. The difference in fermentation profile between the three used carbonate salts was not really significant. The amount of biohydrogen produced was about 22, 22 and 24 g_COD_H2/kg_mixed_liquor when the pH was neutralized by CaCO3, K2CO3 and Na2CO3, respectively.