Simultaneous removal of salt and dissolved petroleum compounds by a two-stage process: spiral wound capacitive deionization three-dimensional electro-Fenton.

Produced water (PW) is the main by-product of oil and gas extraction operations that can be reused. The concentration of ions in produced water is high, so to remove both dissolved minerals and petroleum compounds in the produced water, this study aimed to design and evaluate a two-stage electrochemical process: spiral wound capacitive deionization (SW-CDI), three-dimensional electro-Fenton (3D-EF). The experiments were designed using the Design Expert software version 13, and the effects of five independent parameters on two dependent parameters (desalination and oil removal efficiencies) were investigated. The experimental results were modeled and optimized using the response surface method-central composite design (RSM-CCD). The results showed that the desalination process can be described by a linear two-factor interaction model, while the oil removal process can be described by a quadratic model. At the optimal conditions (an initial salinity of 30 mgL-1, an initial petroleum concentration of 40 mgL-1, a CDI voltage of 1.8 V, an EF voltage of 5 V, and a flow rate of 10.2 mLmin-1), the maximum salt sorption capacity and oil removal efficiencies were 217 mgg-1and 99.9%, respectively. Also, the salt electro-sorption capacity of the CDI reactor is 37 mgg-1, which is more than twice the maximum salt electro-sorption capacity of conventional flow-by CDI reactors (15 mgg-1). Finally, the designed two-stage process removed salt and dissolved petroleum compounds with high efficiency.