Maximizing the production of butyric acid from food waste as a precursor for ABE-fermentation

The current study reports on the maximization of butyric acid production from food waste using a mixed microbial fermentation. In semi-continuous fermentations the effect of three different pH values (5.5, 7.0 and 9.0), three different temperatures (37 degrees C, 55 degrees C and 70 degrees C) and two levels of hydraulic retention time (HRT, 2 days and 6 days) on the formation of butyric acid as well as total volatile fatty acid production (tVFA) were investigated. Overall, pH 5.5 provided the lowest butyric acid concentrations regardless of the temperature and the HRT. At mesophilic temperature (37 degrees C) alkaline conditions (pH 9.0) lead to a strong incline of tVFA as well as butyric acid concentration probably due to a decreased solubilization of the substrate. However, most efficient in terms of butyric acid production was the fermentation conducted at 55 degrees C and pH 7 where a butyric acid concentrations of 10.55 g/L (HRT 2 days) and 13.00 g/L (HRT 6 days) were achieved. Additional experiments at 70 degrees C showed declining butyric acid production. Increase of the HRT from 2 days to 6 days provided an increment of butyric acid concentration throughout almost all experimental settings. However, regarding volumetric productivity the increase in concentration does not compensate for the bigger reactor volume required to establish a higher HRT. At pH 7 and 55 degrees C the resulting volumetric production rates were 5.27 g/L(*)d at a HRT 2 days and only 2.17 g/L(*)d at a HRT of 6 days. (C) 2017 Elsevier B.V. All rights reserved.