Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Alternative techniques for caﬀeine removal from wastewater: An overview of opportunities and challenges Cesar Vinicius Toniciolli Rigueto a , Mateus Torres Nazari b , Camila Favretto De Souza a , Jessica Stefanello Cadore b , Vandré Barbosa Brião a , Jeferson Steﬀanello Piccin b, * a University of Passo Fundo (UPF), Faculty of Agronomy and Veterinary Medicine (FAMV), Postgraduate Program in Food Science and Technology (PPGCTA), Passo Fundo RS, Brazil b University of Passo Fundo (UPF), Faculty of Engineering and Architecture (FEAR), Postgraduate Program in Civil and Environmental Engineering (PPGEng), Passo Fundo RS, Brazil ARTICLE INFO Keywords: Emerging contaminants Adsorption Advanced oxidative process Bioremediation Membrane separation ABSTRACT 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 caf- feine treatment methods have been studied, including adsorption, advanced oxidative processes, bioremedia- tion, 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 limita- tions, often include the complexity of the mechanisms of action, quantiﬁcation of the contaminants in real eﬄuents, and low sustainability of the technique. 1. Introduction Pharmaceutical and personal care products (PPCPs) and endocrine disrupting compounds (EDCs) belong to a class of so-called emerging contaminants owing to their global presence. These contaminants have attracted considerable research attention because they are distributed in surface waters and pose safety risks when consumed owing to their high toxicity and bioaccumulation characteristics in biological tissues, which aﬀect both human and animal health [1,2]. Caﬀeine (1,3,7-trimethylxanthine) is an alkaloid belonging to the methylxanthine family. It is found naturally in coﬀees, teas, chocolate products, and sodas, and is widely consumed because of its stimulating eﬀect on the central nervous system that causes a temporary reduction in drowsiness. In addition, caﬀeine acts on the respiratory and cardio- vascular systems, and is considered a source of risk for patients with cardiovascular disease. It can also cause hyperactivity, depression, and maximize the eﬀects of certain painkillers [3,4]. The average worldwide caﬀeine consumption is around 70 mg per person, with varying consumption depending on the country. Approximately 5% of ingested caﬀeine is excreted in the urine and eventually reaches bodies of water through sewage systems as well as through the disposal of food, beverages, and medicines containing caﬀeine [4–7]. For this reason, caﬀeine can potentially be used to track the level of pollution in a water source [6]. In Italy and Germany, for example, caﬀeine was detected in natural waters at concentrations ranging from 0.6 to 1.056 and 80–265 ng.L -1 , respectively [8,9]. Recent studies have evaluated the eﬀects of caﬀeine exposure on ﬁsh, speciﬁcally investigating its eﬀects on behavior [10], response to robotic stimuli [11], biochemical and genotoxic biomarkers [12], and larval anxiety behavior [13]. It was shown that caﬀeine could interfere with biotransformation mechanisms, decrease locomotor activity at higher doses, and act as a stimulant at lower doses. https://doi.org/10.1016/j.jwpe.2020.101231 Received 12 December 2019; Received in revised form 29 February 2020; Accepted 3 March 2020 ⁎ Corresponding author. E-mail address: jefersonpiccin@upf.br (J.S. Piccin). Journal of Water Process Engineering 35 (2020) 101231 Available online 20 March 2020 2214-7144/ © 2020 Elsevier Ltd. All rights reserved. T