The combination of photocatalysis process (UV/TiO2(P25) and UV/ZnO) with activated sludge culture for the degradation of sulfamethazine

The major factors affecting the removal efficiency of sulfamethazine (SMT) by photocatalysis process in the presence of TiO2 P25 or ZnO, namely the pH, the amount of catalyst and the initial SMT concentration were examined. The obtained results showed the absence of adsorption of SMT on the catalysts and the absence of degradation of SMT by direct photolysis under UV light in the absence of catalyst. The variation of the pH solution in the range 4-9 did not cause any significant degradation of SMT. The optimal amounts of each catalyst were, respectively, 0.5 and 0.25g/L for TiO2 P25 and ZnO. Increasing the initial SMT concentration impacted negatively the removal efficiency, which decreased from 31% to 13% and from 100% to 27% in the presence of TiO2 P25 and ZnO in the presence of 10mg/L and 50 of SMT after 30-min reaction time, respectively. The obtained results showed better efficiency of ZnO than TiO2 P25 regarding both removal efficiency and chemical oxygen demand (COD) abatement. However, removal efficiency and COD abatement were not complete, even after 7h of photocatalysis, about 92% and 41%, respectively. The biodegradability was examined after photocatalysis performed in the following conditions: [SMT](0)=50mg/L, pH=6, T=25 degrees C, =360 rpm and 0.5g/L of TiO2 P25 or 0.25g/L of ZnO. In these conditions, the removal efficiencies were, respectively, 26% and 41% in the presence of TiO2 P25 and 55 and 92% in the presence of ZnO after 4 and 7h of pretreatment times, respectively. The BOD5/COD ratio increased substantially and, respectively, from 0 to 0.25 and from 0 to 0.16 in the presence of TiO2 P25 and ZnO after 7 h of irradiation. Even if the limit of biodegradability (0.4) was not achieved, a subsequent biological treatment was considered in the presence of TiO2 P25, leading to 58% COD abatement after a 28-day culture.