Carbon‐Negative Upcycling of Sewage Sludge into Superiorly Stable Gel Via Liquid‐Phase Utilization Strategy for Water‐Remediation

Sewage sludge utilization holds strategic significance for environmental and sustainable goals. This work presents an integrated low‐temperature sludge hydrothermal coupled with gel crosslinking strategy, which enables stepwise upgrading of sludge resources into water‐treatment materials. Diverging from the current solid‐phase‐only process, this strategy utilizes the organic components in the hydrothermal liquid for co‐crosslinking with sodium alginate, achieving immobilization of hydrothermal constituents. By introducing multifunctional groups and competitively reorganizing the alginate network to expose multidentate adsorption sites, these organic components collectively promote the construction of a hydrothermal‐liquid‐gel capable of forming high‐density metal‐O coordination. The hydrothermal‐liquid‐gel showed up to 47.2% and 368.8% adsorption capacity for heavy metals and antibiotics higher than pure alginate gel, respectively, further reducing residual contaminant concentrations in wastewater by over an order of magnitude. The sludge component in the liquid utilization pathway contributes over three times to pollutant removal that of conventionally focused sludge hydrochar, while maintaining remarkable structure and performance stability across diverse sludge sources through designed regulatory principles. Life cycle assessment and economic analysis demonstrate that sludge integral utilization process maintains economic viability and achieves remarkable carbon reduction benefits. Overall, this work establishes an integrated sludge utilization pathway to construct a sustainable water‐energy‐resource circulation system.