<p>Hazardous waste landfill leachate (HWLL) is a complex and highly polluted form of wastewater generated as a by-product of physical, chemical, and biological processes occurring within hazardous waste landfills. It is characterized by high concentration of pollutants with low biodegradability. The present study investigated the removal of chemical oxygen demand (COD) and total dissolved solids (TDS) from HWLL using the electrocoagulation (EC) process with aluminium (Al), stainless steel (SS), and hybrid Al–SS electrode combinations. Response Surface Methodology (RSM) was employed within the Design of Experiments (DoE) framework to optimise the removal efficiency of COD and TDS for the different electrode combination. The hybrid Al-SS (87.27%) electrode combination demonstrated the highest COD removal efficiency, outperforming Al-Al (66.75%), and SS-SS (63.96%). With respect to TDS removal, the performance across the three-electrode combination was more comparable. The Al-Al achieved a maximum TDS removal efficiency of 76.16%, followed by Al-SS at 73.60% and SS-SS at 70.60% at their optimal conditions. Comparatively, Al-SS combination performed better than other combinations. In addition to the removal efficiency, treatment cost was evaluated based on energy consumption of electrodes during EC process. The Al-SS electrode combination shows the most cost-effective and efficient option having total cost of 0.83 US $/m³ with energy consumption of 0.097 kWh per kg COD removal and 0.036 kWh per kg of TDS removal than other electrode combinations at optimal conditions. The experimental outcomes can be beneficial to the researchers in understanding the use of different electrode combinations in maximizing treatment efficiency of HWLL.</p> Graphical Abstract <p></p>