Developing efficient integrated advanced oxidation processes (AOPs) is vital for sustainable treatment of antibiotic-contaminated water. In this work, a novel 3D photocatalyst was engineered by embedding a ternary Se/g-C3N4/Bi2WO6(SGB) heterojunction into a carboxymethyl cellulose hydrogel, yielding a stable and reusable SGB hydrogel system. Structural, optical, electrochemical, and photoelectrochemical analyses confirmed a hybrid Type-II/Z-scheme heterojunction, reducing the bandgap to 1.74 eV and enhancing charge separation. The synergistic effects of the ternary interface and hydrogel matrix enabled efficient in situ H2O2generation (716 μM in water; 958 μM with isopropanol), facilitating a self-Fenton-like reaction. Upon coupling with peroxymonosulfate (PMS) activation, the system achieved 93.86% tetracycline degradation within 30 minutes. Radical scavenging and trapping experiments revealed a multi-radical degradation pathway involving ˙OH, SO4˙−, O2˙−, and1O2, with their roles modulated by pH. At higher pH, PMS activation via O2˙−/e−favored SO4˙−and1O2generation, while lower pH conditions promoted H2O2/˙OH production and hole oxidation. LC-MS analysis confirmed the stepwise degradation of tetracycline into low-mass intermediates, supporting the proposed mechanism. Toxicity analysis further demonstrated that the transformation products exhibited reduced ecological risk, confirming the environmental safety of the process. The SGB hydrogels exhibited excellent stability and reusability, retaining 72.14% degradation efficiency after 12 cycles and retaining performance across a broad pH range. This study introduces a novel photocatalytic platform integrating Type-II/Z-scheme charge transfer, photoelectrochemical performance, multiple AOP pathways, and progressive detoxification within a hydrogel matrix for sustainable pharmaceutical pollutant remediation.