Sulfamethoxazole removal in membrane-photocatalytic reactor system - experimentation and modelling.

In this study, the efficacy of membrane-photocatalytic reactor (MPR) in sulfamethoxazole (SMX) removal was explored at a fixed initial SMX concentration, i.e. 100 mg/L. A supported catalyst, i.e. TiO2 on granular activated carbon (GAC-TiO2), was used for MPR experiments. The SMX removal efficiency of the MPR was investigated under a range of hydraulic retention time (i.e. HRT from 51 to 152.5 min) and TiO2 catalyst dosage (55-50 mg/L). A maximum SMX removal efficiency of 83.6% was observed under 220 mg/L catalyst dosage and 80 min HRT. The increase in catalyst dosage from 55 to 550 mg/L has increased the transmembrane pressure of the reactor from 9.8 to 22.2 kPa. A multiple non-linear regression model was developed based on the experimental data and its significance was analyzed using two-way ANOVA. Based on the model, the optimal HRT and catalyst dosage for complete SMX removal (100%) were found out. The comparison of photocatalytic degradation experiments with sorption experiments conducted earlier revealed that SMX removal in the MPR was mainly by photocatalytic degradation and not by adsorption onto GAC-TiO2 catalyst. However, the performance of MPR in removing other emerging pollutants from real-time wastewaters could be explored before its field-scale application.

Photocatalytic-oxidation and photo-persulfate-oxidation of sulfadiazine in a laboratory-scale reactor: Analysis of catalyst support, oxidant dosage, removal-rate and degradation pathway.

The extent of sulfadiazine (SDZ) removal via photo-degradation (UV-C), photocatalysis with TiO2 (UV-C/TiO2) and photo-persulfate-oxidation (UV-C/PS) was investigated in a batch reactor under different UV-C power levels (i.e. 14, 28, 42 and 56 W). Moreover, effects of suspended/immobilized catalyst, i.e. TiO2 slurry/TiO2 supported on granular activated carbon (GAC-TiO2), on SDZ removal and corresponding SDZ degradation kinetics under different catalyst loading (1-6 g/L) were explored. Around 41.7% SDZ removal was observed after 120 min in UV-C system at the highest power level, i.e. 56 W. On the other hand, photocatalysis with TiO2 and GAC-TiO2 has shown better SDZ removal than photo-degradation. In UV-C/TiO2 (4 g/L and 28 W) and UV-C/GAC-TiO2 (5 g/L and 28 W) systems, SDZ removals were 91.8% after 120 min and 100% after 60 min, respectively; however, TOC analysis has revealed that 45.4% and 60.8% SDZ was mineralized in these systems, respectively. In UV-C/PS system, near complete degradation of SDZ (99.8%) was observed within 10 min under 50 mg/L of PS and 28 W UV illumination. On the other hand, complete SDZ removal was observed in PS alone system at a dosage of 1000 mg/L but the formation of SO42- was found to be a drawback. In photolysis and photocatalysis systems, SDZ removal followed pseudo-first-order kinetics whereas the kinetics followed pseudo-second-order in UV-C/PS system. The comparison of electrical energy consumed (EEO) in different systems revealed that UV-C/GAC-TiO2 and UV-C/PS system were energy efficient compared with other systems. The LC-MS analysis has confirmed the cleavage of C-N bonds in the pyrimidine ring followed by S-N bonds in the sulfonyl group, which was found to be the major degradation pathway of SDZ.