Comparison of Microbial Diversity, Metabolic Pathways and Methane Production During Anaerobic Digestion Using Untreated and Thermally Hydrolyzed Sludge and Nano Zero-Valent Iron

In this study, thermally hydrolyzed sludge and nanoscale zero-valent iron (nZVI) nanoparticles are combined to assess their impact on enhancing methane production compared with conventional anaerobic digestion without pre-treated sludge and/or nZVI. To this end, 12 digesters were set up for a period of 27 days and divided into four groups, with or without pre-treated sludge and nZVI. To determine the changes in microbiota diversity and metabolic pathways that occurred, DNA shotgun sequencing was carried out. As a results, in the digester containing thermally hydrolyzed sludge and nZVI, methane production was slower but prolonged than with untreated sludge without added nZVI, where it was significantly higher but of shorter duration. Additionally, nZVI addition shortened the lag phase in both sludge types compared to the control digesters. Regarding microbial adaptation, results showed that it was slower in thermally hydrolyzed sewage sludge than in untreated sludge. In terms of microbial diversity, several methanogenic microorganisms have been identified, alongside roughly 75 metabolic pathways directly or indirectly linked to methane production confirming the results achieved related to methane production. the addition of nZVI to thermally hydrolyzed sludge promoted microbial diversity (such as Methanoculleus, Methanobacterium, Methanospirillum, Methanofastidiosum) along with the methane synthesis pathway; these results have been statistically confirmed. Ultimately, the proposed combination proves effective for methane production by improving the availability of nutrients to microorganisms, thereby stimulating the metabolism involved in methanogenesis.