<p>This study investigates the simultaneous removal of Nickel (Ni⁺²), hexavalent chromium Cr(VI), and Chemical Oxygen Demand (COD) from automotive industrial wastewater using an advanced electrocoagulation (EC) process. A key novelty of this work lies in the development of a distinct, optimized iron electrode configuration represented by circular iron electrodes instead of square or rectangular, integrated with optimum operation criterions to maximize pollutant mitigation while minimizing resource consumption. Batch experiments were conducted using iron electrodes on real effluent characterized by baseline concentrations of 12 ± 0.40, 11 ± 0.30 and 2500 ± 75 mg L^− 1 for Ni⁺², Cr(VI) and COD respectively. Through systematic optimization, the critical design criteria for a scalable system were established at an initial pH of 7, a current density (CD) of 3&#xa0;mA cm^− 2 and an electrolysis time of 40&#xa0;min. These optimal parameters successfully balanced peak treatment efficiency with the lowest possible electrode consumption and electrical energy demand. The residual Ni⁺², Cr, COD was 0.096 ± 0.02, 0.025 ± 0.01 and 940 ± 15 mg L^− 1 respectively, while energy consumption reached 1.65 kWh m^− 3 and the electrode consumption was recorded at 0.60&#xa0;kg m^− 3. Transitioning from batch to a continuous-flow regime under optimal batch operating conditions yielded residual concentrations of Ni⁺², Cr and COD was 0.2 ± 0.02, 0.15 ± 0.01 and 915 ± 15 mg L^− 1 respectively, achieving full compliance with stringent national environmental discharge regulations. Techno-economic analysis demonstrated a highly competitive operational cost 0.36 USD m^− 3. Solid-state sludge characterization via SEM, EDX, XRD, and FTIR confirmed the stable immobilization and encapsulation of heavy metals within a robust iron-rich crystalline matrix. Ultimately, the novel electrode geometry and derived design framework provide a technically viable, economically sustainable, and scalable solution for automotive wastewater remediation.</p>