Abstract
The widespread detection of emerging pollutants (EPs) such as antiretroviral drugs (ARVs) and endocrine-disrupting compounds (EDCs) in the aqueous environment has been a significant concern worldwide. These compounds are not removed in conventional wastewater treatment plants (WWTPs) and persist in the environment posing detrimental human health risks and ecotoxicological effects on wildlife and aquatic species. This has raised the need to develop eco-friendly and cost-effective alternative treatment methods to degrade these compounds in wastewater. Advanced oxidation processes (AOPs), including heterogeneous photocatalysis, are among the existing technologies that have, demonstrated success in the remediation of a broad class of EPs. The UV/TiO2/H2O2 hybrid system has shown impressive results in removing some pharmaceuticals and dyes. Although much work has been done in removing EDCs from wastewater, the corresponding removal of ARVs has been less studied.
This study focused on removing EDCs, represented by Bisphenol A (BPA) and ARVs drug residues of emtricitabine (FTC), lamivudine (LVD), Tenofovir (TFV), and nevirapine (NVP) from wastewater using the UV/TiO2/H2O2 advanced oxidation hybrid system. Synthetic wastewater (SW) and fortified natural wastewater (NW) samples were used. Mixed-phase TiO2 was synthesized and used as the photocatalyst. The UV/Visible lamp was utilized as the light source. The central composite design (CCD) of the response surface methodology (RSM) was used to optimize operating variables in SW and analyze the results statistically. Five factors (pH, pollutant concentration, TiO2 loading, H2O2 dosage and irradiation time) were optimized, and the response was specified to be Removal (%). The predicted optimum conditions for the ARVs were pH: 3.0 (FTC, NVP), 5.02 (TFV), and 6.18 (LVD); concentration: 33.64 μg/L (FTC), 50.0 μg/L (LVD), 37.73 μg/L (NVP) and 100 mg/L (TFV); catalyst: 1.03 g/L (FTC), 1.07 g/L (LVD), 1.04 g/L (NVP) and 0.5 g/L (TFV); H2O2: 2.0 % (FTC, TFV), 10.0% LVD) and 5.96% (NVP); irradiation time: 26.11 min (FTC), 60.0 min (LVD), 57.78 min (TFV) and 40.56 min (NVP). For BPA the optimum conditions were pH = 8.25, concentration = 20.0 mg/L, catalyst = 1.5 g/L, H2O2 = 10.0% and irradiation time = 53.33 min. The predicted model was found suitable to represent the degradation of all the pollutants.
In SW, above 80% removals were achieved for all the pollutants under optimum conditions. All the degradations obeyed pseudo-first-order kinetics with k1 of 0.1077 min-1 (FTC), 0.0513 min-1 (TFV), 0.0476 min-1 (LVD) and 0.04084 min-1(BPA). Raising pH and H2O2 up to optimum levels, increased the degradation rate for all the compounds. The h+, •OH, and O2•-
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were the primary drivers of BPA degradation, whereas only •OH and h+ were pivotal for the ARVs. In NW, k1 fell by 12.28- 41.37% for the ARVs and 35.60% for BPA. The results indicate lower degradation rates in NW than SW. Mixed phase TiO2 was synthesized using a low-temperature hydrothermal process. The characterization results were consistent with those of the typical mixed-phase TiO2, with a phase composition of 77.3: 22.7% (anatase:rutile), and average crystallite size of ≈ 12.70 nm (anatase) and 42.13 nm (rutile). In addition, the synthesized mixed phase TiO2 showed a reduced band gap of 3.16 eV compared to 3.20 eV of Anatase. This probably explains the observed extended absorption in the UV-Visible range. The synthesized TiO2 could be reused in 4 successive cycles for the effective degradation all the pollutants from SW and NW, except for BPA which required three cycles in NW. Overall, the optimized UV/TiO2/H2O2 system effectively removed ARVs (FTC, LVD, TFV, NVP) and EDCs (BPA) from SW and NW.