Photocatalytic oxidation is becoming an emerging technology in water and wastewater treatment. Photocatalysis often leads to complete degradation of organic pollutants without any need for chemicals. In this study, the removal of the herbicide metsulfuron–methyl (MM) by photocatalysis was studied. Titanium dioxide (TiO2) was used as a catalyst in a UV reactor equipped with three lamps each with 8 watts of power. The total surface of UV lamps was 537 cm2. The capacity of the photocatalytic reactor was 1.5 L. The effects of parameters such as pH and TiO2 dose on the removal of MM were studied. The combined system of the photocatalytic reactor with powder activated carbon (PAC) adsorption was also investigated. The results indicate that the use of PAC reduced the TiO2 dose and led to very high removal efficiency. A very small dose of 0.05 g/L PAC reduced TiO2 requirement from 2 g/L to less than 0.5 g/L. A detailed molecular size distribution measurement made using high performance size exclusion chromatography (HPSEC) showed that TiO2 can degrade the MM to a small molecular weight compound of 50 daltons within a detention time of 40 minutes. This hybrid system was found to be technically and economically more efficient than the other processes used to remove herbicides and pesticides.

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