Nano-particle based photo-catalytic membrane for removal of organic & microbial pollutants in Water

Abstract

Water is essential for life; however, many people in developing countries, particularly in rural areas, lack access to clean and safe piped water. Untreated potable water often contains biological and chemical pollutants, leading to diseases and even death. Developing eco-friendly technologies using available resources can help address this critical issue. This study aimed to develop and test new nanoparticle-based photocatalytic membranes for point-of-use water treatment systems. Specific objectives were to synthesize and characterize metal-ion-doped TiO 2 photocatalysts coated on polyester membranes, to investigate photocatalytic membrane treatment of wastewater targeting organic and microbial contaminants, to evaluate the disinfection and organic degradation kinetics and synergy of the photocatalytic water treatment, and to assess membrane fouling and reuse potential. TiO 2 , ZnO, and Fe 2 O 3 were successfully synthesized; synthetic and commercial TiO 2 were doped with ZnO and Fe 2 O 3 . The target pollutants were reactive blue dye, oxytetracycline (OTC), and E. coli. Pure and co-doped photocatalysts were incorporated into polyester membranes via an aqueous heat attachment method to enhance antimicrobial properties, photodegradation of organic pollutants, and antifouling capabilities under sunlight irradiation. The photocatalysts and membranes were characterized using Scanning Electron Microscopy (SEM), Energy- Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and UV–Visible Diffuse Reflectance Spectroscopy (UVDRS). Synthetic feed water containing oxytetracycline (1, 2, and 3 mg/L) and E. coli (12 × 10 4 and 6 × 10 4 CFU/100 ml) as well as real dam water containing 13 × 10 3 CFU/100 ml were used for disinfection performance tests. The synergy between the physical filtration of uncoated membranes and the photocatalytic activity of coated membranes (PTFT, PTFC, PTZT, PTZC, and PZ) was evaluated by measuring the synergy index (SI) through log reduction for disinfection and removal efficiency for organic pollutants. The antifouling properties were tested by assessing membrane flux and antifouling performance. Doping enabled visible light absorption, as confirmed by UVDRS analysis TiO 2 displays photo-absorption about 329.9 nm increased by doping to 438.8 nm for TiO 2 /Fe 2 O 3 and 375.5 nm for TiO 2 /ZnO. Solar photocatalytic degradation achieved complete (100%) removal of the dye within 2 hours under solar irradiation for all dye concentrations studied using co-doped photocatalysts. The optimum conditions for degrading OTC were pH 5, flowrate 117 ml/min, and 1 mg/L OTC concentration achieving 96.308% removal. PTZT and PTZC membranes achieved 5-log reduction, the best value observed among uncoated and coated membranes against E. coli in both synthetic and dam water. SI for the disinfection of synthetic and real wastewater were 1.11 to 1.24 and 1.07 to 1.09; and SI for photodegradation of OTC were 1.05 to 1.26 and 1.22 to 1.54 for PTZT and PTFT respectively, doping enhanced membrane fouling resistance, extending usage from 2 cycles to 5, 4, 3, 3, and 2.5 cycles for PTFT, PTFC, PTZT, PTZC, and PZ. In conclusion modifying membranes by incorporating photocatalysis nanoparticles can enhance their antifouling capabilities and improve their overall properties, thereby increasing their effectiveness. Based on the study's findings, doping TiO 2 with Fe 2 O 3 and ZnO is recommended to combine ZnO's antimicrobial properties with Fe 2 O 3 's visible light absorbance.