Abstract
This study explores the mechanisms enhancing phosphorus (P) release from sludge in anaerobic digestion (AD) with thermal hydrolysis pretreatment (THP) using sequential chemical extraction, X-ray absorption near-edge structure spectroscopy (XANES), 31P NMR, and multiomics. THP-treated sludge notably increased liquid-phase P by 53.8% over 3 days compared to sewage sludge (SS), identifying solid-phase Fe-P as the primary P source. The THP+AD also provided a higher abundance of bacteria that contributed to P release through multiple pathways (MPRPB), whereas SS+AD enriched some microbial species with single P release pathway. Moreover, species co-occurrence network analysis underlined the pivotal role of P-releasing bacteria in THP+AD, with 8 out of 16 keystones being P-releasers. Among the 63 screened genes that were related to P transformations and release, the poly beta-hydroxybutyrate (PHB) synthesis genes associated with polyphosphate bacteria-mediated P release were more abundant in THP+AD than in SS+AD. Furthermore, the upregulation of genes involved in methyl phosphonate metabolism in the THP-treated sludge enhanced the methane production potential of the AD process. These findings suggested that MPRPB were indeed the main contributors to P release, and enrichment in the THP+AD process enhanced their capability for P liberation.
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