# Innovative Approaches for Minimizing Disinfection
## 4 DBP Minimization Approaches
### Alternative to Chlorine Disinfectants
#### 4.7.6 Photocatalysis
The photocatalytic process elucidated the observation, degrading higher, more aromatic compounds into smaller, less aromatic ones. Limited photocatalysis, therefore, leads to incomplete oxidation, which subsequently creates intermediate compounds that are more reactive to chlorine. Another pilot-scale study on photocatalysis and enhanced coagulation showed that limited photocatalysis increased THM formation, while extended photocatalysis significantly minimized THMFP. However, the energy consumption was very high in the latter case, rendering the process impractical for full-scale plant implementation. On the other hand, the photocatalytic reduction of THMs requires significantly less energy compared to a decrease in their precursors. Therefore, to balance the mitigation of DBPs, process factors such as chemical dosage, irradiation time, and energy consumption need to be carefully studied and optimized. Another study investigated the photosensitized photodegradation of humic acid (HA). It was reported [44] that the photocatalysis of an HA solution with TiO\({}_{2}\)/UV after 2 h resulted in a 20% reduction in THMFP. On the other hand, the irradiation of an HA solution in the presence of TiO\({}_{2}\) under visible light increased the THMFP of HA. The results suggest that the HAs were chemically transformed in the homogeneous solution under visible light, thereby increasing the THMFP. In another study, the HAAFP of water irradiated with UV light for 30 min was 1.22 times higher than the HAAFP of the raw water. However, it was reduced to 66% because of 60 min of photocatalytic oxidation. Comparing the performance of UV/TiO2 treatment using TiO\({}_{2}\) suspension and nanostructured TiO\({}_{2}\)-coated thin film, the reduction in THMFP for the raw water was around 30% for both the suspended and the fixed UV/TiO\({}_{2}\) treatments. However, in the case of the HAA9 FP, the suspended TiO\({}_{2}\) treatment was more effective (90% reduction) than the fixed treatment. It has also been reported that the formation of THMs in chlorinated water was reduced using photocatalysis before chlorination. The decrease in their formation was attributed to the change in the chemical structure of their precursors, which ultimately became less susceptible to chlorine reactivity. A few studies have also investigated the role of the photocatalytic process in the direct degradation of DBPs. It was observed that the TiO\({}_{2}\) photocatalyst supported on diatomic in nanoscale effectively degraded Br-THMs under Xe light irradiation. The results showed that the Br-THMs were debrominated stepwise. The degradation rate increased significantly with the increase in the degree of substitution of Br-THMs by bromine because the C-Br bond was less stable than the C-Cl bond. THMs were observed to be degraded with the TiO\({}_{2}\) catalyst in combination with sodium persulfate (Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\)) oxidant under solar light. The process effectively degraded tribromomethane (TBM), as only 4% of the initial TBM was recovered in the water after 240 min of TiO\({}_{2}\)/Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\) treatment. In the case of TCM, around 30% remained after 60 min of treatment [44].