Ultraviolet activation of monochloramine to treat contaminants of emerging concern: reactions, operating parameters, byproducts, and opportunities.

The presence of CECs in aquatic systems has raised significant concern since they are potentially harmful to the environment and human health. Eliminating CECs has led to the development of alternatives to treat wastewater, such as advanced oxidation processes (AOPs). The ultraviolet-mediated activation of monochloramine (UV/NH2Cl) is a novel and relatively unexplored AOPs for treating pollutants in wastewater systems. This process involves the production of amino radicals (•NH2) and chlorine radicals (Cl•) from the UV irradiation of NH2Cl. Studies have demonstrated its effectiveness in mitigating various CECs, exhibiting advantages, such as the potential to control the amount of toxic disinfection byproducts (TDBPs) formed, low costs of reagents, and low energy consumption. However, the strong influence of operating parameters in the degradation efficiency and existence of NH2Cl, the lack of studies of its use in real matrices and techno-economic assessments, low selectivity, and prolonged treatment periods must be overcome to make this technology more competitive with more mature AOPs. This review article revisits the state-of-the-art of the UV/NH2Cl technology to eliminate pharmaceutical and personal care products (PPCPs), micropollutants from the food industry, pesticides, and industrial products in aqueous media. The reactions involved in the production of radicals and the influence of operating parameters are covered to understand the formation of TDBPs and the main challenges and limitations of the UV/NH2Cl to degrade CECs. This review article generates critical knowledge about the UV/NH2Cl process, expanding the horizon for a better application of this technology in treating water contaminated with CECs.