# Innovative Approaches for Minimizing Disinfection
## 4 DBP Minimization Approaches
### Alternative to Chlorine Disinfectants
#### 4.7.6 Photocatalysis  
Photocatalytic water treatment has gained significant attention in research, focusing on material synthesis, understanding the mechanism, and designing microreactors. The process has several advantages, including operating under mild conditions, consuming low energy, and having a high potential for mineralization. These qualities appeal to cost-constrained situations, such as in underdeveloped and energy-stressed regions. As a result, researchers are rapidly advancing photocatalytic water treatment technologies to optimize and scale up the process for practical use. The potential to effectively treat water using minimal resources and under ambient conditions has positioned photocatalysis as a promising solution for addressing water quality challenges in areas with limited infrastructure and financial constraints [43]. Photocatalysis with TiO\({}_{2}\) nanoparticles under ultraviolet light (\(\lambda<387\) nm) generates hydroxyl radicals (OH\(\bullet\)) and superoxide radicals (O\({}_{2}\bullet^{-}\)) for oxidation and reduction, respectively. Additionally, the photocatalyst's heterogeneous nature allows for physical adsorption. This process is crucial in mitigating DBPs through decomposition, mineralization, reductive dechlorination, and physical removal of organic precursor substances [26]. TiO\({}_{2}\) photocatalysis can be integrated into a DBP mitigation strategy in various ways, as summarized in Table 1.  
In water treatment facilities, it can be used to remove and mineralize precursor substances, preventing the formation of DBPs through pre-chlorination. It can also mineralize any remaining DBP precursor compounds and destroy actual DBPs before water is released into the distribution network. However, it is important to note that re-chlorination would be necessary after the application of photocatalysis due to the destruction of residual chlorine. It is worth considering that implementing advanced oxidation water treatment, like photocatalysis, may pose economic challenges in situations with relatively high flow rates [26]. Photocatalytic water treatment offers a significant advantage as it only requires water and oxygen as substrates for oxidation. However, despite extensive theoretical research in this area, the practical application of photocatalysis is hindered by several roadblocks. One major challenge is the limited yield of oxidative species due to the recombination of photogenerated electron-hole pairs within the photocatalyst. This limitation has slowed the transition from theoretical research to real-world implementation [43]. One promising approach to enhance photocatalytic oxidation efficiency is combining photocatalysis with chemical oxidants. This strategy has been proposed as an effective means to overcome the limitations imposed by the inherent photogenerated electron-hole recombination within the photocatalyst [43]. Additionally, the photocatalysis process is often combined with other methods, such as coagulation, membrane technologies, and others. It is also gaining popularity for the direct removal of DBPs and their formation potential [44]. The process of heterogeneous photocatalysis combined with oxidant activation requires three key elements: an energy source, a heterogeneous photocatalyst, and a water-soluble oxidant. Research typically utilizes ultraviolet light (UV, wavelengths between 10 and 400 nm) and visible light (Vis, wavelengths between 400 and 780 nm) as the primary energy sources. Different types of lamps, such as low-pressure mercury lamps, LED lamps, and xenon lamps, can generate these energy sources [44]. Heterogeneous photocatalysts are crucial for facilitating the photochemical and redox reactions in this process, as they capture light energy, support charge separation and transfer, and ultimately enable the utilization of the produced charges. The efficiency of the photocatalyst is determined by its ability to absorb light, separate the photogenerated electron-hole pairs, and promote the desired redox reactions [43].