Treatment of produced water using graphene

Abstract

Adsorption is a well-known method for high efficiency in treatment of water and wastewater at low costs. It is a promising method that can compete strongly with conventional purification methods. Carbon-based materials including graphene, graphene oxide, and other nanomaterials have been investigated widely because of their outstanding properties such as chemical permanence, low density and large scale production. Graphene has been extensively used in the treatment of wastewater. In this study, graphene was used as an adsorbent for the removal of emulsified oil from produced water. Experimental work was performed to determine the most suitable method for quantification of emulsified oil in produced water and results showed that the UV-Visible Spectroscopy is the optimum analytical tool in comparison with the Total Organic Carbon (TOC) and Fluorescence Spectrophotometer. In addition, the results showed that the Fluorescence Spectrophotometer is not an appropriate tool to quantify the emulsified oil. Several batch tests were performed on produced water to find the optimum separation conditions by graphene. It was found that these optimum conditions are: contact time = 60 minutes, initial pH = 10.00, graphene dosage =3.00 (g⁄L), salinity = 1500 ppm and temperature 25 0°C with maximum removal efficiency of 80.0%. Fitting of experimental data to different isotherms revealed that the adsorption of emulsified oil using graphene follows Freundlich isotherm with kf=5.29(mg^(1-1/n)L^(1/n)/g) and n=1.66, whereas the adsorption kinetic of emulsified oil is described by the pseudo-second-order kinetic model with a rate constant of 0.020(g/mg.min). Regeneration of graphene was achieved by using n-hexane solvent, and results indicated that the removal efficiency of emulsified oil using graphene decreased from 80.0% to 75.0% and from 75.0% to 71.5%, over two adsorption-regeneration cycles, respectively. Freundlich isotherm gave the maximum adsorption capacity of graphene of 100(mg⁄g).