Biochar and Granular\nActivated Carbon Mitigate Polystyrene\nNanoplastics Inhibition in Dark Biohydrogen Fermentation of Sludge

Nano/microplastics (NPs/MPs) are\ncommonly found in sewage sludge,\nwhich leads to their unavoidable introduction into anaerobic bioreactors\nused for the fermentation or digestion of sludge in bioenergy recovery\nprocesses. This results in oxidative stress on the microbiome, ultimately\nhindering energy recovery. This study investigates the efficacy of\nbiochar (BC) and granular activated carbon (GAC) in enhancing the\ndark hydrogen fermentation of primary sludge while mitigating the\ninhibitory effects of polystyrene nanoplastics (PsNPs). Comprehensive\nanalyses included volatile fatty acid production, microbial community,\ntoxicity, reactive oxygen species (ROS) generation, and sludge dewaterability.\nFor the sludge without PsNPs, the highest enhancement (22.4% over\nthe control) in biohydrogen production was obtained for 5 g/L BC.\nHowever, GAC performed better than BC by achieving the highest recovery\n(64.3%) of biohydrogen production by reducing ROS and toxicity from\nPsNPs. The abundance of Firmicutes in BC- and GAC-amended reactors\nwas linked to higher biohydrogen yields. Also, BC and GAC significantly\nreduced the prolonged capillary suction times observed in the PsNPs-containing\nreactors, demonstrating their effectiveness in enhancing the sludge\ndewaterability. These findings demonstrate the potential of carbonaceous\nadditives, such as BC and GAC, to deliver multiple benefits, including\nboosting biohydrogen production and mitigating the inhibitory effects\nof PsNPs.