Quaternary Treatment of Urban Wastewater for Its Reuse

In today’s ongoing rapid urban expansion, deforestation and climate changes can be observed mainly as unbalanced rain occurrence during the year, long seasons without any rain at all and unordinary high temperatures. These adverse changes affect underground water levels and the availability of surface water. In addition, quite a significant proportion of drinking water is used mainly for non-drinking purposes. With several EU countries increasingly suffering from droughts, reusing quaternary treated urban wastewater can help address water scarcity. At the European level, Regulation 2020/741 of the European Parliament and of the Council of 25 May 2020 on minimum requirements for water reuse was adopted. This regulation foresees the use of recycled wastewater mainly for agricultural irrigation. This article provides an overview of various processes, such as filtration, coagulation, adsorption, ozonation, advanced oxidation processes and disinfection, for quaternary treatment of urban wastewater in order to remove micropollutants and achieve the requirements for wastewater reuse. According to the literature, the most effective method with acceptable financial costs is a combination of coagulation, membrane filtration (UF or NF) and UV disinfection. These processes are relatively well known and commercially available. This article also helps researchers to identify key themes and concepts, evaluate the strengths and weaknesses of previous studies and determine areas where further research is needed.