Journal of Water Process Engineering 40 (2021) 101959 Available online 23 February 2021 2214-7144/© 2021 Published by Elsevier Ltd. Experimental investigation of crude oil removal from water using polymer adsorbent Hadis Mottaghi a , Zahra Mohammadi a , Mojgan Abbasi a, *, Nassim Tahouni b , M. Hassan Panjeshahi b a Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran b School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran A R T I C L E INFO Keywords: Adsorption Chitosan Oil Produced water Hydrogel ABSTRACT While extracting oil and gas from underground reservoirs, a large amount of water is produced, which increases during the reservoir’s life. Given the scarcity of water supplies and the high volumes of water produced, proper management and usage in various applications are essential. The main objective of this study is to adsorb the remaining oil from produced water using a biodegradable polymer of chitosan. The hydrogel of chitosan and polyethylene glycol was synthesized with different ratios of 1:1, 2:1 and 3:1 and epichlorohydrin was used as cross-linker. The ratio of 3:1 of chitosan/polyethylene glycol was chosen as the optimum, which had the highest adsorption capacity. To improve effciency and hydrophobicity of the synthesized hydrogel, multi-walled carbon nanotubes were also added, and fnally, the chitosan/polyethylene glycol/multi-walled carbon nanotubes composite was synthesized. The synthesized adsorbent was characterized using FTIR, FE-SEM, and BET analyses, and the results indicated that modifcation was successful. The results showed that the addition of multi-walled carbon nanotubes in the structure of hydrogel increases the hydrophobicity and surface area up to 20 times. The results of batch adsorption studies specifed that the maximum adsorption capacity occurs at pH = 3, oil con- centration and adsorbent dosage of 1 g/l. Moreover, the isotherm and kinetics studies revealed that the process obeys Langmuir isotherm and the pseudo-second-order model. 1. Introduction Among different sources of energy, oil and gas are the primary ones. Demands for these fossil energy sources have increased due to the development of technology and accelerated industrialization [1,2]. Oil and gas industry causes severe environmental problems, especially during production and transportation. Despite oil and gas signifcance, releasing of spilled oil and oily wastewater into waterways and seas has become a signifcant concern in recent decades [3]. Moreover, a large volume of oily wastewater produced during oil and gas extraction causes signifcant issues that need special attention [1,4]. Globally, about 250 million barrels per day of produced water (PW) are produced from both oil and gas felds, which is projected to increase to 340 million barrels by 2020 [5]. Proper management and usage in different applications are crucial because of the scarcity of water supplies and a considerable volume of PW [6]. PW is the most signifcant wastewater generated during oil and gas extraction, and releasing it in the environment has harmful effects on the ecosystem, humans, plants, and microorganisms. The contaminants in the PW are similar to the oil or gas adjacent to the reservoir, and the amount of these materials can vary signifcantly in different wells. The pollutions in the PW come from two primary sources: 1 Contaminations due to the natural properties of water produced from oil reservoirs such as dissolved and dispersed organic compounds, dissolved minerals including heavy metals, naturally occurring radioactive materials (NORMs) and Anions and Cations. 2 The chemicals used during the production process are complex mixtures of hazardous compounds. Some of these chemicals are: biocides, scale inhibitors, corrosion inhibitors, emulsion breakers and surfactants [4,7] These contaminants affect the ecosystem; according to the environ- mental regulations, standards have been laid down to control the * Corresponding author. E-mail address: mojganabbasi@ut.ac.ir (M. Abbasi). Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe https://doi.org/10.1016/j.jwpe.2021.101959 Received 14 October 2020; Received in revised form 26 January 2021; Accepted 29 January 2021