Effect of Solution pH and Influence of Water Hardness on Caffeine Adsorption onto Activated Carbons Osorio Moreira Couto Jr., 1 * Inês Matos, 2,3 Isabel Maria da Fonseca, 2 Pedro Augusto Arroyo, 1 Edson Antônio da Silva 1 and Maria Angélica Simões Dornellas de Barros 1 1. Departamento de Engenharia Química, Universidade Estadual de Maringá, Av. Colombo, 5790 87020‐900, Maringá, Paraná, Brazil 2. Departamento de Química, REQUIMTE‐CQFB, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516, Caparica, Portugal 3. Instituto Politécnico de Setúbal, ESTBarreiro, 2839‐001, Barreiro, Portugal There has been little research into the effects of the water hardness and pH of surface waters on the adsorption of caffeine on activated carbons. The aim of this study was to determine the influence of these water characteristics on different activated carbons. Caffeine adsorption from the aqueous phase was studied using biomass derived activated carbons (DD: dende coco and BB: babassu coco) and a commercially available activate carbon (NO: Norit 1 GAC 1240 plus). The functionalized carbons in an inert atmosphere was also studied and were denominated DI, BI, NI. Results highlight the importance of pH in caffeine adsorption: the highest removals were obtained for pH 3.0 and decrease for higher pH. The adsorption isotherms obtained were fitted to the Freundlich and Langmuir models. Calcium and magnesium ions were adsorbed to a varied extent on the activated carbons. The hardness in solution decreased their adsorption due to a competition effect. K F and q m from the Freundlich equation linearly decreased with water hardness due to salt‐screened electrostatic repulsions between charged molecules. The amount adsorbed from deionized water was largest because there was no competition between inorganic ions and molecules. Keywords: activated carbons, water hardness, caffeine, adsorption kinetics INTRODUCTION O rganic micropollutants as pharmaceutical compounds are present in the environment and, due to the increasing concentration detected in recent studies, are a rising concern among researchers and regulatory agencies. Most of them are not yet regulated and their impact on aquatic flora, animals, and human life is not quite known. Wastewater treatment plants were not designed to specifically remove drugs from wastewater. Although some may be reduced, others apparently are not. Caffeine is considered a chemical marker for surface water pollution because it is regularly consumed around the world. Therefore, it is one of the most abundant xenobiotics in untreated wastewater effluents together with its metabolite paraxanthine and the non‐steroidal anti‐inflammatory drug acetaminophen. [1] In order to remove these emerging contaminants from waste- waters, varied physicochemical techniques have been proposed. Adsorption is an efficient and versatile method for the removal of low concentrations of organic pollutants from industrial waste- waters. Among commercial adsorbents, activated carbon is the most commonly used adsorbent. Adsorption on activated carbon has proven successfully in removing caffeine from aqueous solutions, showing a high adsorption capacity. [2] Water being an essential resource for life in all ecosystems, a great effort has been made in the past decades to modify the water sector technologies in order to improve the water quality. In this sense, adsorption has become a well‐established technique to remove pollutants, activated carbon being the prevailing adsorbent for the purification of water with low pollutant concentration. The major drawbacks are a poor economic feasibility, limited applicability and effectiveness, and a short lifetime, often due to low and expensive regeneration capacities. Generally, the loaded carbon is regenerated ex situ by heating or steaming, which is a high energy‐consuming process and, although the efficiency is relatively high, there is a considerable loss of activated carbon. [3] The last decade has seen a continuous improvement in the development of effective noble adsorbents in the form of activated carbon, [4] zeolites, [5] clay minerals, [6] chitosan, [7] lignocellulo- ses, [8] natural inorganic minerals, [9] and functionalized poly- mers. [10] However, most of these adsorbents are either not effective (due to diffusion limitation or the lack of enough active surface sites) or have shown problems like high cost, difficulties of separation from wastewater, or generation of secondary wastes. An alternative is to use low‐cost adsorbents with at least reasonable performance to be costly effective. [11–13] In this work, two widely produced residues were used for the preparation of low‐ cost high‐value carbon materials: babassu coconut shell and dende coconut shell. Babassu and dende are typical Brazilian palm trees that produce vegetal oils used in medicine, food, and even biodiesel. After the extraction process, the shells are burned to obtain babassu and dendê activated carbons used as adsorbents in dissolved organic removal, as pesticides, herbicides, or insecticides used in agriculture, heavy metals, and pharmaceuticals in wastewater treatment. *Author to whom correspondence may be addressed. E‐mail address: osorio_eq@yahoo.com.br Can. J. Chem. Eng. 93:68–77, 2015 © 2014 Canadian Society for Chemical Engineering DOI 10.1002/cjce.22104 Published online 14 November 2014 in Wiley Online Library (wileyonlinelibrary.com). 68 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING VOLUME 93, JANUARY 2015