Microbiological mechanisms of sludge property variations under long-term landfill: From micro-omics perspective

Landfill sludge (LS) with high moisture content is non-standard and insecure, necessitating the investigation of characteristic variation mechanisms to guide its further treatment. In this study, the degradation rules and property changes of raw dewatered sludge (RDS) and solidification sludge (SDS) with varying landfill ages (3–10 years) were systematically explored using physicochemical index, organic compositions, and micro-omics. The results revealed that the permeability and fluidity of LS dropped early with a high concentration of extracellular polymeric substances (EPS) from the lysis or metabolite of microorganisms. Then they rose remarkably at the post stage of the landfill when the degradation of EPS was dominant with looser sludge flocs, illustrating that fresh and aged LS required dewatering conditioners with destructive and aggregation capacity, respectively. Two-dimensional correlation spectroscopy of IR spectroscopic indicated that the hydrophilic substances in SDS were degraded antecedent to hydrophobic substances, while the opposite trend was observed in RDS, contributing to better permeability. Discrepancies between metagenomic and metaproteomic data suggested dominant functional hydrolytic bacteria and methanogens within RDS as landfill age turned to substrates due to insufficient EPS excretion, leading to sludge disintegration tendencies. While the activity of these phyla was effectively kept in SDS, resulting from that the curing agent facilitated the initial release of EPS and expedited anaerobic reaction processes, which contributed to the improved dewaterability after the long-term landfill. The results provide new insights and research strategies for comprehending the nature variation mechanisms of LS, and thus informing the technical protocol of the re-dewatering process.