Nano zerovalent iron boosts methane content in biogas and reshapes microbial communities in long-term anaerobic digestion of pig slurry
Míriam Cerrillo, Míriam Guivernau, Laura Burgos, V. Riau, August Bonmatí Blasi
Abstract
Adding nanoscale zero-valent iron (nZVI) to the anaerobic digestion (AD) process for livestock manure has been shown to significantly enhance methane content by influencing microbial communities and metabolic pathways. However, the long-term effects of nZVI on metabolically active microbial communities remain largely unexplored. This study explored these microbial shifts in nZVI-supplemented AD systems and biogas composition under both mesophilic and thermophilic conditions over extended operation. To this end, three lab-scale continuous stirred tank reactors were operated for 265 days using raw pig slurry as the feedstock. Two mesophilic reactors received 84 mg g SSV -1 of nZVI, while a third thermophilic reactor received 42 mg g SSV -1 . High-throughput sequencing and quantitative PCR were employed to monitor changes in bacterial and archaeal communities following nZVI addition. The results demonstrated a notable increase in methane content in the biogas, reaching 88% in mesophilic and 87% in thermophilic conditions with nZVI. Microbial responses differed between reactors, including increased copy numbers of metabolically active archaeal mcrA and bacterial 16S rRNA genes, as well as a rise in the relative abundance of specific genera, such as Methanosaeta . These findings underscore the potential of nZVI to enhance AD performance through targeted shifts in microbial community structure and function.