Biohydrogen Production from Anaerobic Fermentation - Biotechnology in China: Biofuels and Bioenergy - page 157

Fig. 2 Process diagram of the integrated hydrogen production, microbial electrolysis cell
(MEC), and microbial fuel cells (MFCs)
sugars, 215 (based on glucose); ethanol, 2,379; acetate, 740; propionate, 351;
butyrate, 204; valerate, 20. Before the effluent was fed into the MEC reactor, it was
centrifuged to remove biomass and the pH was adjusted from 4.5-4.6 to 6.7-7.0
using PBS. With use of a single-chamber MEC at 0.6 V, the hydrogen production
rate was 1.41 m 3 H 2 /m 3 /day and the overall hydrogen recovery was 83% based on
both electrical energy and substrate utilization. For the whole coupling system of the
fermentation and the MEC, the hydrogen production rate was 2.11 m 3 H 2 /m 3 /day
and the overall hydrogen recovery was 96%. The energy efficiency was up to
287% based on the electrical energy input. However, the study also showed that
little hydrogen was produced when the effluent was directly fed from the ethanol-
type fermentation to the MEC system because of the low pH.
Wang et al. [ 96 ] developed a multiple coupling system integrating dark
fermentation, MFCs, and an MEC together (Fig. 2 ). Hydrogen was firstly pro-
duced in continuous dark fermentation at a yield of 10 mmol H 2 /g cellulose, which
consumed about 71% cellulose. The COD of the fermentative effluent was
7,005 mg/L, of which 69% was volatile fatty acids, including acetic, propionic,
butyric, and valeric acids, and ethanol. The pH of the effluent was 5.3, which was
adjusted to 7.0 before the effluent was fed into the MFCs and the MEC. The
effluent feeding into the MFCs generated a voltage of 0.43 V, which powered the
MEC for hydrogen production at a yield of 33.2 mmol H 2 /g COD. The overall
hydrogen production for the integrated system was increased by 41% compared