Reactor-Ready Photocatalytic Wastewater Treatment: Cross-Scale Benchmarking of Catalyst Performance, Photon Utilization, Hydrodynamics, Safety, and Sustainability

Heterogeneous photocatalysis can transform persistent aqueous contaminants through light-driven charge generation and interfacial oxidation–reduction reactions. Modified oxides, heterojunctions, and supported catalysts may improve spectral use, carrier separation or recovery, although these benefits depend on the water matrix and reactor geometry. This structured critical review proposes an application-specific reactor-readiness framework connecting catalyst synthesis and deployment to photon allocation, hydrodynamics, matrix interference, safety, durability, and whole-system burden. It evaluates slurry, immobilized, membrane-integrated, and structured catalysts in annular, flat-plate, compound-parabolic, falling-film, packed-bed, and internally illuminated configurations. The framework distinguishes between intrinsic material activity, observed reactor performance, and delivered treatment service, and proposes a six-domain performance and seven iterative decision gates. Published cases are used illustratively; sparse comparable photon, hydraulic, toxicity, and lifetime data preclude a pooled quantitative ranking. Priorities are paired real-water comparisons, explicit photon and energy boundaries, transformation-product and effect-based measurements, and durable operation at defined treatment endpoints.