Prussian Blue–Alumina as Stable Fenton-Type Catalysts in Textile Dyeing Wastewater Treatment

Textile dyeing effluents are characterized by recalcitrant organics and high salinity, requiring robust pretreatments prior to biological polishing. The heterogeneous Fenton-type (HFT) oxidation over Prussian Blue nanoparticles supported on γ-alumina (PBNP/γ-Al2O3) was investigated in a liquid batch-recycle packed-bed reactor treating a synthetic textile wastewater (STW) reproducing an industrial dye bath with the Reactive Black 5 (RB5) dye, together with simplified RB5 and RB5 + NaCl matrices. Hydrogen peroxide decay followed pseudo-first-order kinetics. Using fixed initial doses (11, 20, 35 mmol L−1), the catalyst exhibited an early adaptation phase and then reproducible operation: from the fourth reuse onward, both the H2O2 decomposition rate constant and DOC removal varied by <10% under identical conditions. Among matrices, STW exhibited the highest oxidant efficiency. With an initial H2O2 dose of 11 mmol L−1, the treatment enabled complete discoloration and produced effluents with negligible toxicity. Increasing the initial dose to 20 or 35 mmol L−1 did not improve treatment and led to a decrease in the hydrogen peroxide decomposition rate with reuses and loss of PB ν(C≡N) Raman bands, indicating surface transformation. Overall, PBNP/γ-Al2O3 demonstrated reproducible activity and structural resilience in saline, dyeing-relevant matrices at H2O2 doses that preserve catalytic integrity, confirming its feasibility as a stable and reusable pretreatment catalyst for saline dyeing effluents, and supporting its integration into hybrid AOP–biological treatment schemes for dyeing wastewater.