Thermophilic-operating environment promotes hydrogen-producing microbial growth in a lignocellulose-fed DF-MEC system for enhanced biohydrogen evolution

This current work investigated the effects of increasing temperature on microbial biofilm composition during the conversion of the lignocellulosic agricultural wastes into biohydrogen using a dark-fermentation and Microbial electrolysis cell integrated system bio-catalyzed by a mixed culture. The reactors were operated under a thermophilic environment (R-Th) and directly compared with the reactors operated under mesophilic conditions (R-Me). The R-Th anodic biofilm composition was dominated by thermophilic lignocellulose-degrading and hydrogen-producing microorganisms belonging to the phyla of Proteobacteria (37.82 %), Thermotogota (35.94 %), and Coprothermobacteria (8.3 %) whereas the same phyla were noticeably less represented under mesophilic conditions. Compared to R-Th, R-Me anodic biofilm was characterized by more diverse microbial communities, and concomitantly promoted the proliferation of the methanogenic archaeal genera including Methanosarcina sp. (71.87 %), Methanothermobacter sp. (17.23 %), Methanomethylovorans sp. (8.35 %), Methanobrevibacter sp. (0.97 %), Methanobacterium sp. (0.79 %), Methanosphaera sp. (0.28 %), and Methanosaeta sp. (0.28 %). These results clearly show that the agricultural waste-fed DF-MEC integrated reactors performed under a thermophilic environment significantly promoted thermophilic-hydrogen producing microbial communities and inhibited the hydrogen-consuming microbial growth, which thus enhanced hydrogen yield. This work will significantly help the practitioners in selecting the suitable operating temperature during the fermentative conversion of agricultural wastes into biohydrogen energy on a large scale.

Automated summary

This study investigated the effects of increasing temperature on microbial biofilm composition during the conversion of agricultural wastes into biohydrogen. The results showed that operating the reactors under a thermophilic environment significantly promoted thermophilic-hydrogen producing microbial communities and inhibited the hydrogen-consuming microbial growth. The study provides valuable insights for the large-scale fermentative conversion of agricultural wastes into biohydrogen energy.