Environmental impact assessment of advanced urban wastewater treatment technologies for the removal of priority substances and contaminants of emerging concern: A review

Abstract

Conventional urban wastewater treatment plants are not designed to remove micropollutants, which may have more long-term effects than previously thought. Advanced treatment technologies (such as ozonation) are being employed at full scale to solve this issue. Nevertheless, one must consider the resources and energy additionally needed when implementing these systems and, as a consequence, the further environmental burdens. The negative contributions must be minimized so that the solution to the initial problem does not result in other environmental impacts, and a tool suitable for this analysis is the life cycle assessment (LCA), taking into consideration the full life cycle of these processes. A literature review on the status of LCA application for advanced treatment of wastewater was performed in this study, with focus on the removal of priority substances (PSs) and contaminants of emerging concern (CECs) of the Directive, 2013/39/EU, and the Watch List on the Decision, 2015/495/EU of March of 2015 updated by the Decision, 2018/840/EU of June of 2018. In total, 65 substances were included in this research. Only 18 papers were found considering the environmental benefits (in terms of avoided impacts) of the removal of such compounds by specific advanced treatments (mainly ozonation, Fenton-based and granular activated carbon processes) and only 33 of the mentioned substances were included in these studies. The lack of information on the effects that these pollutants and their transformation products can have on living beings, compromises the LCA application and leads to an underestimation of avoided impacts. Generated impacts result mainly from the production of energy (and the respective energy mix) and the use of some specific reagents such as hydrogen peroxide. Some promising alternatives might be solar-based treatments and other reagents/materials (e.g. carbon-based materials as catalysts); however, studies are scarce, especially in terms of alternative chemicals. Many processes have yet to be assessed with this approach, including heterogeneous photocatalysis, along with combinations of different treatment options. For example, no studies were found regarding the LCA of electrochemical oxidation, hydrodynamic cavitation, among others, for the removal of PSs and CECs considered in the present review.