In this work, photocatalytic materials constituted by Cr-doped TiO₂ (Cr-TiO₂) decorated with noble metals show high effectiveness in the mineralization of Acid Orange 7 (AO7) and in the disinfection of real river water. The materials were firstly obtained by sol-gel method to get Cr-TiO₂ that was subsequently modified by photochemical deposition of Ag or Pd nanoparticles (Ag/Cr-TiO₂, Pd/Cr-TiO₂). Chemical-physical characterization results evidenced that the noble metals were homogeneously distributed on the Cr-TiO₂ surface. By using Pd(0.25%)/Cr-TiO₂, the AO7 discoloration efficiency was about 91.4% after only 60 min of visible irradiation, which can be due to the lowest band gap of this material. Moreover, nitrates, chlorides, total hardness, and coliform bacteria content significantly decreased after the treatment of real river water samples (that is contaminated by industrial and domestic effluents) under UV and visible light irradiation in the presence of TiCrOx decorated with noble metals. One hundred percent of elimination rate for E. coli, total coliforms, and other enterobacteriaceae (without regrowth) was achieved by using Ag/Cr-TiO₂ as photocatalyst.

In the present study were evaluated a biological treatment and several Advanced Oxidation Technologies (AOTs), including TiO₂/UV-VIS, H₂O₂-UV-VIS and TiO₂/H₂O₂/UV-VIS for industrial wastewater treatment. The experiments were carried out both in a laboratory reactor and in a 120 L/s pilot plant with autonomous operation under solar energy. The individual application of the biological treatment using a commercial bacteria strain led to a significant decrease in total hydrocarbons, sulfates, total organic carbon (TOC), hardness, alkalinity, biochemical oxygen demand (BOD5), and chemical oxygen demand (COD), in the starting industrial wastewater sample. It was also observed that the application of UV-VIS/H₂O₂/TiO₂ as combined treatments, is more effective than biological treatment and individual AOTs reducing certain quality parameters, such as conductivity, chlorides, nitrates, turbidity, fats and oils, total suspended solids, settleable solids, acidity, TOC, total coliform bacteria and in the removal of heavy metals (Zn, Cu, Cr, Ni, Fe, Pb). In addition, the use of a sequential treatment, initially applying a AOTs and subsequently a biological treatment, resulted in an improvement in the removal of contaminants such as chlorides, heavy metals (Fe, Pb), nitrates and hardness. Thus, the results suggest that the sequential combination of AOTs and biological treatment is an effective strategy for the recovery of industrial wastewater, achieving a greater reduction of contaminants compared to the application of each treatment separately, thus improving the final quality of the treated water.