Modified-Tio2 Photocatalytic Membrane for Disinfection and Degradation of Organic pollutants in wastewater

Abstract

The increasing microbial and persistent emerging organic contaminants presence pose detrimental effects on the environment and ecosystem, such as diseases and toxicity. Conventional water treatment methods are ineffective, necessitating advanced techniques such as photocatalysis and membrane processes. This study aimed to synthesize and apply solar photocatalytic membranes for disinfection and degradation of organic pollutants in wastewater. The specific objectives were to: synthesize and characterize nitrogen-doped titanium dioxide nanoparticles and membrane; determine optimum conditions for degradation and disinfection of pollutants in wastewater using solar photocatalysis and filtration; and assess the performance of the photocatalytic membranes, durability, and reuse. Nitrogen-doped nanoparticles(N-TiO2) were synthesized and immobilized onto the polyvinylidene fluoride (PVDF) membrane. Characterization was by Fourier transform infrared spectra, X-ray diffraction, water contact angle, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX). The combined effects of pH and sodium chloride (NaCl) concentration were modelled and optimized for two experimental sets with N-TiO2-PVDF. Sulphamethoxazole degradation, flux and TOC removal were responses for 1st and E.coli removal and flux for 2nd sets. N-TiO2-PVDF performance was assessed at pH 4-10, 6-14 mg/l sulphamethoxazole and 2.6x108 -10.4x108 CFU/l E.coli. N-TiO2-PVDF reuse and durability was assessed with 5 repeated cycles of 6mg/l sulphamethoxazole and 10.4x108 CFU/l E.coli removal. Nitrogen doping red-shifted the light absorption to a visible range of 440nm. Nitrogen dopant was detected at 1170 cm-1 for N-TiO2 and 1346-1417 cm-1 for nitrogen-doped titanium dioxide PVDF(N-TiO2-PVDF) membrane. SEM-EDX identified 0.01wt% nitrogen in N-TiO2-PVDF. The water contact angle reduced by 81.39o because of polyvinyl alcohol and N-TiO2. The analysis of variance had high predictability with R2 of 0.73, 0.93 and 0.75 for 1st set, and 0.83 for 2nd set, with coefficients of variance under 10%, indicating adequate response variation. The optimum conditions for 1st set were pH 4.6 and 7.8 g/l NaCl for 76.5% degradation, pH 4.6 and 7.8 g/l NaCl for 9.8 ml/7cmD/min flux and, pH 7.3 and 11.7 g/l NaCl for 58% TOC removal. The optimum condition for 2nd set was pH 4.6 and 7.8 g/l NaCl for 5.3 ml/7cmD/min flux. However, E.coli removal could not be modelled due to total E.coli elimination by size exclusion. Sulphamethoxazole's highest degradation and relative flux were 81.31% and 0.77 at pH 4, caused by the surface charges enhancement and N TiO2 antifouling. 65.0% highest TOC removal was at pH 7 and attributed to degradation intermediates properties. 6mg/L sulphamethoxazole had the highest degradation of 69.87%, 0.73 relative flux and 69.87% TOC removal, and depended on the N-TiO2 inactivation and foulants. E.coli highest disinfection was 99.04%(2.017 log reduction) at pH 7 and at 0.3017 relative flux, and attributed to weak repulsive surface charges and N-TiO2 antifouling. 2.6x108 CFU/l E.coli had 96.15%(1.415 log reduction) highest disinfection and relative flux of 0.42 and attributed to light hindrance and bio-fouling. N-TiO2-PVDF had a decline of 10.13% degradation, 0.29 relative flux and 13.59% TOC removal, and of 1.92% disinfection and 0.07 relative flux with reuse cycles. In conclusion, N-TiO2-PVDF effectively eliminated pollutants and with high durability and reuse. More antifouling, decontamination and reuse clean-up strategies on N-TiO2- PVDF are recommended