*Article* **Wastewater Treatment by Advanced Oxidation Process and Their Worldwide Research Trends**

**José Antonio Garrido-Cardenas 1,\* , Belén Esteban-García 2,3, Ana Agüera 2, José Antonio Sánchez-Pérez 2,3 and Francisco Manzano-Agugliaro <sup>4</sup>**


Received: 26 November 2019; Accepted: 23 December 2019; Published: 25 December 2019

**Abstract:** *Background*: Water is a scarce resource and is considered a fundamental pillar of sustainable development. The modern development of society requires more and more drinking water. For this cleaner wastewater, treatments are key factors. Among those that exist, advanced oxidation processes are being researched as one of the sustainable solutions. The main objective of this manuscript is to show the scientific advances in this field. *Methods*: In this paper, a systematic analysis of all the existing scientific works was carried out to verify the evolution of this line of research. *Results*: It was observed that the three main countries researching this field are China, Spain, and the USA. Regarding the scientific collaboration between countries, three clusters were detected—one of Spain, one of China and the USA, and one of Italy and France. The publications are grouped around three types of water: industrial, urban, and drinking. Regarding the research, 15 clusters identified from the keywords analyzed the advanced oxidation process (alone or combined with biological oxidation) with the type of wastewater and the target pollutant, removal of which is intended. Finally, the most important scientific communities or clusters detected in terms of the number of published articles were those related to the elimination of pollutants of biological origin, such as bacteria, and of industrial nature, such as pesticides or pharmaceutical products.

**Keywords:** reclaimed water; advanced oxidation process; microorganisms; concern emergent contaminant; worldwide
