A new perspective on evaluating the critical roles of sludge hydrochar (SH) and powdered activated carbon (PAC) in anaerobic granular sludge (AnGS) reactor: Focusing on operational stability, sludge characteristics and strengthening mechanism.
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75% confidenceThis study evaluates the use of sludge hydrochar (SH) and powdered activated carbon (PAC) in anaerobic granular sludge (AnGS) reactors, finding that SH improves methane production and operational stability, but becomes unstable at high organic loading rates due to sludge washout.
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Abstract
Enhancing methane production (MP) in anaerobic digestion (AD) systems largely relies on improving electron transfer between bacteria and methanogens, yet conductive materials' acceleration effects and stability pose challenges for practical use. This study constructed continuous-flow reactors to evaluate conductive material sustainability by analyzing reactor performance and sludge characteristics under different organic loading rates (OLR), with stable mechanisms elucidated via enzyme activity, microbial community, and functional gene variation. Results revealed that the SH-mediated reactor (R SH ) achieved the highest COD removal (97.0% ± 1.8%) and methane production (6.7 ± 0.2 L/d) at a high OLR of 48.7 ± 1.2 kg/(m 3 ·d) by enriching Desulfomicrobium (19.5%) and Methanothrix (54.4%), promoting acetoclastic methanogenesis (AM) via conductive-pili gene expression. However, under ultra-high OLR, R SH became unstable due to sludge washout caused by excessive extracellular polymeric substance (EPS) secretion (184.3 ± 22.1 mg/L), which further inhibited MP activity of remaining microbes. In contrast, the PAC-mediated reactor (R PAC ) maintained stability under ultra-high OLR by leveraging PAC's inherent conductive properties and upregulating cytochrome-C and flavin-protein genes, facilitating direct interspecies electron transfer (DIET) between Clostridium (64.9%) and hydrogenotrophic methanogenesis (HM) archaea (60.5%). Both SH and PAC enhanced the performance of AD reactors; nonetheless, R SH exhibited limited OLR stress resilience due to its enhanced AD pathway having excessive metabolic activity, whereas R PAC demonstrated robust performance through the reinforced syntrophic propionate oxidation (SPO)-HM pathway. This study highlighted the balance between the strengthening effect of conductive materials and sustainability in AD optimization, which advanced understanding of conductive material applicability, offering practical insights for sustainable anaerobic digestion technologies.