Evaluation and enhancement of hydrogen production from Vietnamese macroalgae in the single-stage of dark fermentation and microbial electrolysis cell

Macroalgae-derived hydrogen (H 2 ) has emerged as a potential energy source due to its cleanness and sustainability. Vietnam has a long coastline with a wide variety of macroalgae, possibly suitable for sustainable H 2 production. To evaluate and promote H 2 production from Vietnamese macroalgae, the single-stage dark fermentation (DF) and microbial electrolysis cell (MEC), namely sDFMEC, was applied for the first time in this study. Three common species were examined, including Gracilaria tenuistipitata (Rhodophyta), Sargassum polycystum (Phaephyta), and Ulva lactuca (Chlorophyta). The results showed that S. polycystum exhibited the best performance with an H 2 yield of 472.4 ± 9.2 mL/g-VS. Furthermore, to enhance the performance of S. polycystum -fed sDFMEC, intermittent energy input (I-E app ) mode and chloroform (CHCl 3 ) addition were also investigated. The results revealed that with a proper duty length ranging from 1 to 60 min, I-E app mode could improve H 2 production and energy efficiency of sDFMEC. Meanwhile, the presence of CHCl 3 at 30 ppm almost completely inhibited methane (CH 4 ) generation in sDFMEC and maintained this inhibitory effect without further addition for the following 8 batch cycles (∼300 h). Accordingly, applying these enhancement methods improved the H 2 yield and overall energy recovery by around 150% and 170%, respectively. However, small amounts of CH 4 (∼0.5–1% v/v) were still detected regardless of the high CHCl 3 concentrations (up to 100 ppm), suggesting reactor design optimization is required. Besides, more eco-friendly inhibitors with a similar mechanism and the process's economics should also be further investigated.