# Innovative Approaches for Minimizing Disinfection
## 4 DBP Minimization Approaches
### Alternative to Chlorine Disinfectants
#### 4.7.6 Photocatalysis
This treatment involves a series of reactions with dissolved iron as the catalyst, hydrogen peroxide and solar radiation. Solar photo-Fenton can deactivate pathogens that are highly resistant to conventional disinfection methods, including Bacillus subtilis, phytopathogenic fungi, antimicrobial-resistant bacteria and genes, and viruses found in surface water and wastewater [42]. Presently, the advancement of solar photochemical processes, particularly those utilizing solar light, is regarded as being of dynamic importance. AOPs founded on photocatalysis have been demonstrated to be a compelling tool for eliminating chemical and biological contaminants from water. They have garnered considerable attention. Remarkably, heterogeneous photocatalysis (HP) is described as \"chemical reactions induced by a solid material (photocatalyst) that absorbs appropriate radiation and remains unchanged throughout the process\". TiO\({}_{2}\) and ZnO are the most commonly utilized semiconductors as photocatalysts for solar applications in environmental settings. The primary advantage of these technologies is their ability to eliminate/reduce pollutants through mineralization, unlike other traditional processes where the pollutant is simply transferred to the environment. Hydroxyl radicals (HO\(\bullet\), E\({}_{0}\) = 1.9-2.8 V vs. NHE) and other highly oxidizing species like the superoxide anion (O\({}_{2}\bullet\)-) and hydroperoxide (HO\({}_{2}\bullet\)) are responsible for oxidizing organic pollutants. In environmental applications, the sulfate radical anion, SO\({}_{4}\bullet^{-}\) (E\({}_{0}\) = 2.5-3.1 V vs. NHE), can also play a role when persulfate (S\({}_{2}\)O\({}_{8}\)\({}^{2-}\)) or peroxymono-sulfate (HSO\({}_{5}\)\({}^{-}\)) are used as oxidants. Hydroxyl radicals (HO\(\bullet\)) and sulfate radical anions (SO4\(\bullet^{-}\)) have half-lives of 10-3 and 30-40 \(\upmu\)s, respectively. While both typically engage in electron transfer reactions, hydroxyl radicals can also react through hydrogen atom abstraction [30]. As per [PERSON] et al. [30], even though THMs are highly volatile and photodegradable compounds (with removal percentages ranging from 86% to 54% for TCM and TBM after 4 h of stirring in the dark), the application of solar heterogeneous photocatalysis using commercially available photocatalysts like the semiconductor materials ZnO and TiO\({}_{2}\), in combination with a potent oxidant such as Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\), significantly improves their elimination in drinking water. The primary advantage of AOPs is their ability to restrict or reduce pollutant content through mineralization, unlike conventional methods that merely transfer pollutants from one location to another. The removal percentages after the photolytic test (4 h) varied between 63 and 92% for trichormethane (TCM) and tribromomethane (TBM). When photocatalysts were utilized, ZnO/Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\) exhibited greater effectiveness compared to TiO\({}_{2}\)/Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\) in degrading chlorinated species (TCM,bromodichloromethane-BDCM, and dibromochloromethane-DBCM), while no significant differences were observed for TBM. Using photocatalysis before the disinfection step can reduce the levels of NOM and other DBP precursors, ultimately limiting the formation of DBPs in the disinfected water. [PERSON] and [PERSON] [44] observed a 57% reduction in river water's THMFP after 12 h of photocatalysis using fluidized TiO\({}_{2}\) particles. More than 90% reductions in THMFP and haloacetic acid formation potential (HAAFP) using a mechanically driven photocatalytic reactor within 60 min of irradiation time have also been reported. Integrated photocatalysis into a microfiltration reactor significantly reduced THM formation potential (66-69%) for synthetic and natural water samples. Employing a nanofiltration membrane after the photocatalytic reactor further reduced the formation potential. In another study, the THMFP of the surface water was significantly increased within 15 min of photocatalysis.