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A low-cost micro porous graphite air diffusion cathode (MPGADC) has been utilized successfully for the in-situ hydrogen peroxide generation via O 2 reduction in 0.05 M Na 2 SO 4. Using a tubular electrochemical reactor with a novel design composed of MPGADC as a cathode and a hollow cylinder porous graphite as an anode, a maximum of 68 mg/ L of H 2 O 2 was produced at a current density of 25 mA/cm2, an air flow rate of 3 L/min, and a pH value of 3. Electro-Fenton (EF) process was adopted to remove the chemical oxygen demand (COD) from the wastewater of Al-Dora petroleum refinery in Iraq using this new style of tubular electrochemical reactor. Based on the response surface methodology (RSM) with Box-Behnken design (BBD), the effect of EF operating parameters on the COD removal was investigated. The optimal conditions for maximizing COD removal efficiency (RE%) with lowering specific energy consumption (SEC) using EF process were determined to be a current density of 6.66 mA/cm2, Fe2+ concentration of 0.80 mM, and an electrolysis duration of 60 min, in which RE% of 94% with SEC of 3.75 kWh/kg COD were achieved. In addition, the results demonstrated that the current density has the greatest influence on the COD removal, followed by electrolysis duration and then Fe2+ concentration. Furthermore, current density has the greatest impact on the specific energy consumption, followed by time, while Fe2+ concentration has a negligible effect. The high R2 value (98.33%) confirmed the goodness of fitting the model equation. These results established the viability of employing the new cathode design for the EF process in treatment of petroleum refinery wastewaters. [Display omitted] • Low-cost micro porous graphite air diffusion cathode was utilized for COD removal from wastewater using electro Fenton. • The effects of various operational parameters on COD removal(RE%) were evaluated and optimized by RSM. • The new cathode generated a maximum of 68 mg/ L of H 2 O 2 at current density of 25 mA/cm2 and air flow rate of 3L/min. • Current density has the greatest influence on the RE%, followed by electrolysis duration and Fe2+ concentration. • The optimal conditions were current density of 6.66 mA/cm2, Fe2+ concentration of 0.80 mM, and 60 min, in which RE% and SEC were 94% and 3.75 kWh/kg COD. [ABSTRACT FROM AUTHOR]