Visible and solar light photocatalytic disinfection of bacteria by N-doped TiO₂

A water treatment system was developed based on a photocatalytic process, employing immobilized N-doped TiO₂, which worked under solar radiation. Batch reactor studies were conducted using an immobilized and suspended form of N-doped TiO₂. Activities of Degussa P-25 and N-doped TiO₂ were compared. Optimization of catalyst concentration was also carried out. Reaction rates under different working conditions were compared. The bacterial kill followed a pseudo first-order reaction. Continuous reactor studies were carried out using N-doped TiO₂ coated glass plates. Three-log inactivation of bacteria was obtained after a contact time of 40 min. The effects of turbidity, bicarbonate ions and organic matter were studied. It was found that the efficiency of the system decreased due to these components. Comparison of the performance of solar water-disinfection (SODIS) and solar photocatalytic treatment for disinfection of water was also carried out. The results showed that the suspended catalyst achieved complete inactivation in 1 h compared to SODIS which took 6 h. Bacterial regrowth was observed in the case of SODIS treatment whereas no bacterial growth was observed after solar photocatalytic treatment.