*3.3. Industrial Technologies*

The establishment photocatalytic depollution technology is a very difficult task due to the fact that real industrial conditions and parameters are less stable and controllable than laboratory conditions, with few companies (Purifics Photo-Cat) applying AOP in industry [194,195]. There is a need to develop pilot scale-up systems that can confirm the technologies presented in this review and eventually be able to use them in industrial applications. Also, another aspect that needs attention is whether photocatalysis will be used alone or as an intermediary step (pre or post-treatment) in a depollution process (maybe used together with ozonation or with physical or biological processes [208].

Conventional photocatalytic nitrate reduction techniques have been developed to produce potable waters, such as adsorption, ion exchange, chemical reduction, membrane filtration, electrochemical, and biological denitrification [209]. These conventional techniques further produce secondary toxic by-products. One of the main problems in the practical application of photocatalysts is the development of methodology for photoreactor scale-up [210]. There are some chemistry, material, and reactor challenges currently limiting large-scale applications of photocatalysis processes of inorganic pollutants [203].

Figure 18 summarizes the challenges and future perspectives to improve photocatalytic remediation technologies.

**Figure 18.** Schematic representation of the challenges and photocatalytic approaches in depollution technologies.
