Alternative techniques for caffeine removal from wastewater: An overview of opportunities and challenges

[Display omitted] Water contaminants have attracted considerable research attention owing to the safety risks they pose when present in drinking water consumed by humans and animals, where their high toxicity and bioaccumulation characteristics in biological tissues can cause severe health problems. Caffeine is an emerging contaminant due to its high consumption by the general population, and it can be used to track pollution caused by humans. Approximately 5% of ingested caffeine is excreted through the urine as it cannot be completely metabolized. The caffeine removal efficiency of conventional wastewater treatment methods varies with the system. In addition, studies have reported higher caffeine concentrations in water resources than in water treated in wastewater treatment plants, indicating that effluents are being illegally discharged into rivers. Therefore, alternative caffeine treatment methods have been studied, including adsorption, advanced oxidative processes, bioremediation, and membrane separation. This paper presents a literature review of methods for caffeine removal from aqueous solutions and real effluents, and it covers the main results and limitations of each method. The Scopus database was used to identify relevant articles on caffeine removal. Through the review, it is concluded that even with promising application trends, the current methods developed for caffeine removal present several limitations, often include the complexity of the mechanisms of action, quantification of the contaminants in real effluents, and low sustainability of the technique.