Enhanced semi-continuous hydrogen production by addition of microplastics under mesophilic and thermophilic fermentation.

• Effects of microplastics (MPs) on the semi-continuous H 2 production were investigated. • Mesophilic and thermophilic H 2 production were enhanced in MPs supplemented groups. • MPs can favor the H 2 -producing bacterial growth and optimize the microbial community. • The highest semi-continuous H 2 production rate reached 4.85 L L−1 d−1. In this study, the influences of polyethylene terephthalate microplastics (PET MPs) on the semi-continuous hydrogen (H 2) production and microbial community under mesophilic and thermophilic fermentation were investigated. Results indicated that PET MPs can enhance the semi-continuous H 2 production performance, and the highest H 2 production rates in mesophilic and thermophilic MPs supplemented groups were 4.85 and 3.6 L L−1 d−1, which were 21.6% and 63.6% higher than the control groups, respectively. Moreover, it was found that PET MPs could favor the growth of H 2 -producing bacteria and optimize the microbial community structure. In mesophilic MPs supplemented groups, the abundance of genus Lactococcus and Ethanoligenens increased from 20.77% and 6.7% to 38.69% and 10.78%, respectively. The abundance of genus Thermoanaerobacterium became the dominant bacteria in thermophilic fermentation, and its abundance increased from 9.02% to 69.38%. This work provides novel insights into the function of MPs in fermentative H 2 production system. [ABSTRACT FROM AUTHOR]