Persulfate-enhanced lanthanum iron oxide-mediated photocatalysis can effectively degrade an aqueous industrial dye and mineralize water and wastewater

A novel, home-made lanthanum iron oxide (LF; 0.125-1.00 g/L) was used to treat an industrial model pollutant (Reactive Black 5 dye-RB5; C-o = 20 mg/L) under UV-A irradiation (1.3 W/L). Aqueous, hydrolyzed RB5 solution that was prepared to mimic reactive dyehouse effluent could be successfully degraded by LF-mediated photocatalytic treatment and the degradation rate was remarkably enhanced in the presence of persulfate (PS; 0.6-1.2 mM). LF-mediated heterogeneous photocatalysis was only effective at pH <= 4. The dissolved organic carbon (DOC) content of the aqueous RB5 solution (DOCo = 5.15 mg/L) could also be substantially removed by LF/UV-A (LF = 0.5 g/L; 52%-54% DOC removal after 150-180 min) and PS-enhanced LF/UV-A (LF = 0.5 g/L; 60%-66% DOC removal after 120 min). Reuse of the same LF photocatalyst for complete color and partial DOC removals was confirmed for the selected LF/UV-A/pH3 and LF/PS/UV-A/pH3 treatment conditions in four treatment cycles. LF/UV-A/pH3 and LF/PS/UV-A/pH3 were also applied to real water and wastewater samples; tap water (DOCo = 1.98 mg/L) and two secondary treated sewage (DOCo = 5.39 and 16.83 mg/L) samples. A decrease in DOC removals to 25% (tap water), 22% (secondary treated, low-DOC sewage sample) and 5% (secondary treated, high-DOC sewage sample) was observed for the real water and wastewater samples.