The Study of Produced Water Treatment Using Integrated Electro Fenton – Granular Biological Method

Produced water is the largest waste stream in the oil and gas industry. It is a mixture of inorganic and organic pollutants. The harmful effects of discharging untreated produced water on the environment and public health is a challenging concern. Nowadays, the integration of advanced oxidation process and biological treatment is of interest to the researchers. Investigating the relationship between AOP pretreated effluent and subsequent bioreactor performance can help to optimize these systems. In this research, biological treatment was first examined without pretreatment, and it was found that biological degradation alone is incapable of treating the sample, so the integrated method of electro fenton-biological treatment was studied. Electro fenton performed the pretreatment and bioreactor did the final treatment. Synthesized MCNT-Ce/WO3/GF cathode and the MWCNT/GO/Fe3O4 heterogeneous catalyst were used in the electro fenton process. BTEX removal test - as a produced water simulant - was done using aerobic granules bioreactor, electro fenton and their combination, respectively. After optimizing the pH and time variables, in order to study the interactive effects of temperature, catalyst load, applied current and electrodes distance, a Box-Behnken experimental design and response surface methodology were used to optimize the performance of proposed system. The experiment carried out in the calculated optimal conditions for the electro-fenton degradation process (temperature 30 °C, catalyst load 250 mg/L, current density 170 mA/m2 and electrode distance 1.5 cm). The BOD/COD ratio and COD removal was found to be 0.41 and 56.5%, respectively. In these conditions, effluent entered the granular bioreactor and the final COD removal of the sample was done up to 94%. Real produced water was fed into the electro-fenton reactor and its effluent was introduced to the aerobic granular bioreactor, results showed that integrated electro fenton-bioreactor removes organic pollutants up to 92.7± 0.2% and keeps the characteristics of the treated produced water within the environmental standard range.