Statistical modelling and optimization of photodegradation of sulphamethoxazole using nitrogen-doped titanium dioxide-polyvinyl deflouride photocatalytic membrane

Increasing water demand, and the presence of bio-recalcitrant antibiotics contaminants have detrimental effects on health, water quality, and the environment. Novel nitrogen-doped titanium dioxide polyvinylidene difluoride photocatalytic membrane (NTiO2-PVDF) was applied in the photodegradation of sulphamethoxazole antibiotic. The combined effects of pH and NaCl concentration and were modelled and optimized by Response surface methodology (RSM) based on central composite design (CCD). Sulphamethoxazole (SMX) degradation, flux and total organic carbon (TOC) removal were the responses. Flux was modelled with linear polynomial model and quadratic polynomial models modelled degradation and TOC removal. The Analysis of Variance had high predictability in all the models with differences in predicted R2 and adjusted R2 not exceeding 0.2, and the coefficient of variance (CV%) in all the models not exceeding 10% indicating adequate variation and reliability in responses. The optimum values were 76.5% degradation at pH 4.6 and 7.8 g/l sodium chloride concentration, flux of 9.8 ml/7cmD/min at pH 4 and 7.0 g/l sodium chloride concentration, and 58% TOC removal at pH 7.3 and 11.7 g/l sodium chloride concentration. Moreover, NTiO2-PVDF had an overall 32.9% drop in flux within 1 h of degrading 10 mg/l SMX solution. To our knowledge, this is the first study that investigated the combined effects of pH and NaCl concentration using CCD based on RSM with sulphamethoxazole and visible light active nitrogen doped-PVDF photocatalytic membrane to understand interactions of factors that exist in real wastewater matrix.