Urban sewage sludge-derived TiO₂-based composites for simultaneous wastewater treatment and photocatalytic hydrogen production

Sewage sludge management and sustainable hydrogen production are challenges in the transition to a circular economy. To the best of our knowledge, this study investigates an innovative sludge valorization strategy based on the selective recovery of Ligno-Humic-Like compounds (LHLs) from sewage sludge and their conversion into LHLs-derived biochars (BCs) for integration into TiO₂-based photocatalysts for simultaneous wastewater treatment and hydrogen production. LHLs were extracted from sewage sludge and converted into BCs by thermal treatment. TiO₂ was precipitated onto surfaces of LHLs and BCs, yielding two classes of TiO₂-based composites, followed by in situ Cu photodeposition to modify the photocatalytic properties and enhance hydrogen production from organic substrates and real wastewater matrices. Photocatalytic performance was evaluated using glycerol (1000 ppm) as a sacrificial electron donor under simulated solar irradiation (500 W m⁻²), reaching 850 μmol H₂ g⁻¹ TiO₂ h⁻¹ . An investigation using several classes of organic compounds found in wastewater streams resulted in hydrogen production of up to 1086 μmol H₂ g⁻¹ TiO₂ h⁻¹ and 95.1% pollutant removal (for HCOOH). Physicochemical characterization indicated that the incorporation of BC and Cu modified the surface and optical properties of the TiO₂-based composites, consistent with enhanced photocatalytic performance. The selected photocatalyst showed higher activity retention than Degussa P25 under the investigated recycling conditions and was evaluated using four wastewater matrices for feasibility screening, followed by testing with real biodiesel wastewater. This work presents an integrated approach to sewage sludge valorization, hydrogen production and wastewater treatment, highlighting its potential integration within a circular economy framework.