High rate acidogenic fermentation in an up-flow anaerobic sludge bed reactor at extremely low pH

Abstract

Volatile fatty acid (VFA) platform has drawn much attention and it has been confirmed that VFA production by mixed-culture acidogenic fermentation at low pH has several advantages. The metabolic mechanisms and stability of acidogenic fermentation at low pH was investigated by a continuous stirred tank reactor (CSTR) fed with glucose with pH controlled at 4.0 (day 1–28), 5.0 (day 29–42) and 4.0(day 43–62). Results indicated lactate fermentation and ethanol fermentation coexist when pH was controlled at 4.0. Lactobacillus was the dominant bacteria. However, when pH in CSTR reactor was increased and controlled at 5.0, the fermentative type changed. In order to improve the efficiency of acidogenic fermentation at low pH, a up-flow anaerobic sludge bed (UASB) reactor was operated with glucose as feeding material and the organic loading rate (OLR) of UASB gradually increased and eventually was high up to 42 g/(L.d). When operated at OLR of 42 g/(L.d) and HRT of 4 h, the UASB reactor was found with a higher VFAs yields of 16.4 gCOD/(L.d), which was much higher than CSTR reactor. In addition, acidogenic granular sludge successfully appeared in UASB reactor at extremely low pH of 3.2~4.0. Lactobacillus was also predominant in the acidogenic granular sludge of UASB reactor, which was similar with CSTR reactor, however, biohydrogen-producing bacteria also took large proportion.