Mechanisms and performance evaluation of oily sludge biodegradability enhanced by hydrothermal treatment

This study developed a hydrothermal treatment (HT) strategy to address the poor biodegradability of high-liquid-content oily sludge. Hydrothermal temperature effects were evaluated through petroleum hydrocarbons, heavy metals, microbial communities, and functional genes in the sludge. The results indicated that elevated temperatures effectively disrupted the sludge's emulsion system and promoted organic matter removal. However, excessive temperatures (>210 °C) induced polycondensation reactions, generating recalcitrant polymers that compromised biodegradability. HT significantly altered the chemical forms of heavy metals. Temperature increases facilitated the conversion of Cr to less bioavailable residual form, enhancing biodegradation potential. The microbial analysis revealed that Proteobacteria and Achromobacter became the dominant taxa after HT, with the abundance of hydrocarbon-degrading genes peaking at 170 °C. Biodegradation tests confirmed a 24 % increase in hydrocarbon degradation at 170 °C compared with untreated sludge. Thus, HT at 170 °C effectively enhances sludge biodegradability, demonstrating the potential of combined hydrothermal-bioremediation for eco-friendly sludge disposal.