## 6 Future Perspectives  
The elimination of parabens and other CECs has been studied using different AOP technologies over the years by different authors. However, much research must be done before these can be easily implemented with low costs and in an environmentally friendly manner. In general, and regarding the treatment of parabens, it seems that the use of catalysts should be preferred to the use of radiation or reagents alone. Furthermore, to lower the catalyst cost, it is important to guarantee that these can be used several times and can be recovered, regenerated, and reused. The use of radiation and catalyst should be considered depending on the technique to be applied, since some technologies, such as photocatalysis, need radiation to work. If the catalyst can be activated by solar radiation, the costs related to these technologies should be lower and attractive for industrial implementation. The common catalyst that is reported (TiO\({}_{2}\)) cannot be activated by this type of radiation or by visible radiation, but it is already known that this can be possible with catalyst doping. Furthermore, another thing to turn the industrial application closer is the use of immobilized catalysts, since the most used ones are present in powder form, and this can make industrial application difficult, since the powder will need more separation and recovery units, which can be traduced into more equipment, energy, labor, or resuming more operational and investment costs. During the use of different AOPs, it is noticed that the poor mineralization and the increase in toxicity can occur due to the generation of more (toxic) by-products (or, in other words, the lack of complete oxidation into CO\({}_{2}\) and H\({}_{2}\)O). This parameter should always be considered since it is possible to remove the wanted target compounds while, on the other hand, generating more toxic compounds that, when released into the environment, could have a worse impact than the initial pollutant's solution. Moreover, in the AOP treatment designs, the associated costs (investment and operational costs) are another important evaluation parameter for the choice of the technology to be used. In fact, one major disadvantage of this group of advanced treatments is the associated high costs, especially related to energy and reagents consumption; this problem needs to be overcome in order to make these technologies feasible. Furthermore, in some of the countries already affected by water scarcity, the costs may be the biggest obstacle for advanced wastewater treatment technologies. With this, there are many parameters that need to be considered and optimized for the implementation of these technologies on an industrial scale, but it is important that in the near future, the implementation of easily operational, efficient, low-cost, and environmentally friendly AOPs technologies be applied for real wastewater treatment. So, for future perspectives, it is important to  
* Produce high-performance catalysts with lower costs;
* Dope and support catalyst to allow their reuse and the use of other types of radiation, such as solar radiation;
* Produce cheaper and more eco-friendly radiation sources;
* Test different types of reactors and operational parameters;
* Test different AOP technologies for the same effluent on a real scale;
* Study in depth the toxicological effects in different species and impacts in the environment;
* Study in depth the operational economics for different technologies. Based on the reviewed works, regarding parabens' treatment (which may not be applied to other CECs or real wastewater solutions due to the diversity of compounds presented in wastewaters from different places), authors appear to be focused on photo-catalysis and ozone-based solutions.