Biochar and Granular Activated Carbon Mitigate Polystyrene Nanoplastics Inhibition in Dark Biohydrogen Fermentation of Sludge

Nano/microplastics (NPs/MPs) are commonly found in sewage sludge, which leads to their unavoidable introduction into anaerobic bioreactors used for the fermentation or digestion of sludge in bioenergy recovery processes. This results in oxidative stress on the microbiome, ultimately hindering energy recovery. This study investigates the efficacy of biochar (BC) and granular activated carbon (GAC) in enhancing the dark hydrogen fermentation of primary sludge while mitigating the inhibitory effects of polystyrene nanoplastics (PsNPs). Comprehensive analyses included volatile fatty acid production, microbial community, toxicity, reactive oxygen species (ROS) generation, and sludge dewaterability. For the sludge without PsNPs, the highest enhancement (22.4% over the control) in biohydrogen production was obtained for 5 g/L BC. However, GAC performed better than BC by achieving the highest recovery (64.3%) of biohydrogen production by reducing ROS and toxicity from PsNPs. The abundance of Firmicutes in BC- and GAC-amended reactors was linked to higher biohydrogen yields. Also, BC and GAC significantly reduced the prolonged capillary suction times observed in the PsNPs-containing reactors, demonstrating their effectiveness in enhancing the sludge dewaterability. These findings demonstrate the potential of carbonaceous additives, such as BC and GAC, to deliver multiple benefits, including boosting biohydrogen production and mitigating the inhibitory effects of PsNPs.