# Innovative Approaches for Minimizing Disinfection
## 4 DBP Minimization Approaches
### Alternative to Chlorine Disinfectants
#### 4.7.6 Photocatalysis
AOPs, such as TiO\({}_{2}\) photocatalysis, are based on generating non-specific radical species capable of oxidizing a wide range of pollutants. In photocatalysis, UV light with a wavelength of less than 387 nm irradiates a semiconductor photocatalyst, producing highly reactive radical species such as <<OH [22; 26]. Additionally, the heterogeneous nature of TiO\({}_{2}\) allows for physical adsorption on its surface, contributing to a multifaceted treatment approach. The effectiveness of photocatalysis in mitigating DBP depends on the concentration and composition of NOM in the influent, which can vary significantly as untreated water undergoes various physicochemical treatment processes [22]. In many instances, the significant contribution to DBP formation comes from hydrophilic and lower molecular weight fractions. The application of photocatalytic treatment tends to alter the composition of NOM towards these components. According to [PERSON] et al. [22], there was an observed shift in the hydrophilic fraction from 15 to 90% after undergoing photocatalytic treatment. Consequently, even after photocatalysis, DBPs can continue to form and surpass initial levels. [PERSON] et al. [22] also noted a rise in TTHM formation by as much as 75% when employing limited photocatalysis (65 kWh m\({}^{-3}\)) for raw water treatment. However, with higher energy levels, there was a substantial decrease in DBP formation, leading to a 95% reduction in TTHMs. Unfortunately, this enhanced performance required a significant amount of energy, which could make it economically unfeasible for applications in high-flow water treatment. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Precursor Removal** & **Combined Use with** & **Efficiency Improvements** & **Direct Removal of DBPs** \\ \hline During prechlorination & Chemical oxidants & Solar photo-Fenton & Best results for brominated species \\ Before distribution network & Coagulation & TiO\({}_{2}\) and ZnO semiconductors & \\  & Membranes & & \\ \hline
**Limitations** & & & \\ \hline NOM shift to hydrophilic fractions \(\rightarrow\) favors DBPs formation & & & \\ Increased energy consumption \(\rightarrow\) increased costs & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Incorporation of photocatalysis in DBP mitigation. By optimizing sequential treatment processes with restricted TiO\({}_{2}\) photocatalysis after conventional treatment methods like adsorption and filtration, it is possible to focus on eliminating/destroying both hydrophobic and hydrophilic fractions. This approach can effectively reduce DBP formation and simultaneously minimize the usage of system inputs such as chemicals and energy [22]. Towards the conclusion of the previous century, photocatalysis surfaced as an alternative or supplementary technology to conventional disinfection methods. Photocatalysis, categorized as an AOP, can be classified into heterogeneous and homogeneous processes. In both scenarios, sunlight can be harnessed to stimulate the production of hydroxyl radicals (\(\bullet\)OH), known for their potent disinfect characteristics. In water, pathogen inactivation occurs during heterogeneous photocatalysis with a photocatalyst and UV radiation. Although several catalysts have been experimented with, TiO\({}_{2}\) remains the most extensively researched in disinfection procedures. Nevertheless, when sunlight is employed as the energy source for heterogeneous photocatalysis, the efficiency of the process is diminished. This is because photocatalysts are predominantly activated by UV radiation, which accounts for only 3-5% of sunlight. The efficiency of the process significantly improves when the catalyst is in the form of suspended micro- or nanoparticles. These particles can be immobilized to prevent nanoparticle contamination; however, immobilization restricts large-scale applications compared to homogeneous processes. The most extensively studied process in homogeneous solar photocatalysis is solar photo-Fenton treatment.